BQ2040SN-C408TR - Texas Instruments

Features

➤Provides accurate measurement

of available charge in NiCd,

NiMH, and Li-Ion batteries

➤Supports SBS v1.0 data set and

two-wire interface

➤Monitors charge FET in Li-Ion

pack protection circuit

➤Designed for battery pack inte-

gration

-Low operating current

-Complete circuit can fit on less

than ¾ square inch of PCB

space

➤Supports SBS charge control

commands for NiCd, NiMH, and

Li-Ion

➤Drives a four-segment LED dis-

play for remaining capacity

indication

➤16-pin narrow SOIC

General Description

The bq2040 Gas Gauge IC With

SMBus Interface is intended for

battery-pack or in-system installa-

tion to maintain an accurate record

of available battery charge. The

bq2040 directly supports capacity

monitoring for NiCd, NiMH, and Li-

Ion battery chemistries.

The bq2040 uses the System Man-

agement Bus v1.0 (SMBus) protocol

and supports the Smart Battery

Data (SBData) commands. The

bq2040 also supports the SBData

charge control functions. Battery

state-of-charge, remaining capacity,

remaining time, and chemistry are

available over the serial link.

Battery-charge state can be directly

indicated using a four-segment LED

display to graphically depict battery

full-to-empty in 25% increments.

The bq2040 estimates battery self-

discharge based on an internal

timer and temperature sensor and

user-programmable rate informa-

tion stored in external EEPROM.

The bq2040 also automatically re-

calibrates or “learns” battery capac-

ity in the full course of a discharge

cycle from full to empty.

The bq2040 may operate directly

from three nickel chemistry cells.

With the REF output and an exter-

nal transistor, a simple, inexpensive

regulator can be built to provide

VCC for other battery cell configu-

rations.

An external EEPROM is used to

program initial values into the

bq2040 and is necessary for proper

operation.

bq2040

Gas Gauge IC With SMBus Interface

VCC 3.0–6.5V

ESCL EEPROM clock

ESDA EEPROM data

LED1-4 LED segment 1-4

VSS System ground

SR Sense resistor input

DISP Display control input

PN204001.eps

16-Pin Narrow SOIC

VCC

ESCL

ESDA

LED1

LED2

LED3

LED4

VSS

VOUT

REF

SMBC

SMBD

PSTAT

DISP

SB Battery sense input

PSTAT Protector status input

SMBD SMBus data input/output

SMBC SMBus clock

REF Voltage reference output

VOUT EEPROM supply output

SLUS005–JUNE 1999 E

Pin Connections Pin Names

Pin Descriptions

VCC Supply voltage input

ESCL Serial memory clock

Output used to clock the data transfer be-

tween the bq2040 and the external non-

volatile configuration memory.

ESDA Serial memory data and address

Bidirectional pin used to transfer address

and data to and from the bq2040 and the ex-

ternal nonvolitile configuration memory.

LED1–

LED4

LED display segment outputs

Each output may drive an external LED.

VSS Ground

SR Sense resistor input

The voltage drop (VSR) across pins SR and

VSS is monitored and integrated over time

to interpret charge and discharge activity.

The SR input is connected to the sense re-

sistor and the negative terminal of the

battery. VSR <V

SS indicates discharge, and

VSR >V

SS indicates charge. The effective

voltage drop, VSRO, as seen by the bq2040

is VSR +V

OS. (See Table 3.)

DISP Display control input

DISP high disables the LED display. DISP

floating allows the LED display to be active

during charge if the rate is greater than

100mA. DISP low activates the display for

4 seconds.

SB Secondary battery input

Monitors the pack voltage through a high-

impedance resistor divider network. The

pack voltage is reported in the SBD register

function Voltage (0x09) and is monitored for

end-of-discharge voltage and charging volt-

age parameters.

PSTAT Protector status input

Provides overvoltage status from the Li-Ion

protector circuit and can initiate a charge sus-

pend request.

SMBD SMBus data

Open-drain bidirectional pin used to transfer

address and data to and from the bq2040.

SMBC SMBus clock

Open-drain bidirectional pin used to clock

the data transfer to and from the bq2040.

REF Reference output for regulator

REF provides a reference output for an op-

tional FET-based micro-regulator.

VOUT Supply output

Supplies power to the external EEPROM con-

figuration memory.

bq2040

Functional Description

General Operation

The bq2040 determines battery capacity by monitoring

the amount of charge put into or removed from a re-

chargeable battery. The bq2040 measures discharge

and charge currents, estimates self-discharge, and

monitors the battery for low-battery voltage thresholds.

The charge is measured by monitoring the voltage

across a small-value series sense resistor between the

battery's negative terminal and ground. The available

battery charge is determined by monitoring this voltage

over time and correcting the measurement for the envi-

ronmental and operating conditions.

Figure 1 shows a typical battery pack application of the

bq2040 using the LED capacity display, the serial port,

and an external EEPROM for battery pack program-

ming information. The bq2040 must be configured and

calibrated for the battery-specific information to ensure

proper operation. Table 1 outlines the configuration in-

formation that must be programmed in the EEPROM.

An internal temperature sensor eliminates the need

for an external thermistor—reducing cost and compo-

nents. An internal, temperature-compensated time-

base eliminates the need for an external resonator,

further reducing cost and components. The entire cir-

cuit in Figure 1 can occupy less than 34square inch of

board space.

bq2040

VCC VOUT

REF

SMBC

SMBD

PSTAT

DISP

ESCL

ESDA

LED1

LED2

LED3

LED4

bq2040

VSS

2040LED.eps

301K BSS138

100K

86.5K

604K

806K

604K

499K

806K

499K

604K

909K

BSS138

2N7002

BSS138

2N7002

R5 R4 Q1R11

No. of Cells

Chart 1

For bq2040 With No D8

Li-IonNiMH

499K

698K

806K

909K

(Optional)

Figure 1. Battery Pack Application Diagram—LED Display

bq2040

Parameter Name Address Description Length Units

EEPROM length 0x00 Number of EEPROM data locations

must = 0x64 8 bits NA

EEPROM check1 0x01 EEPROM data integrity check byte, must = 0x5b 8 bits NA

Remaining time alarm 0x02/0x03 Sets RemainingTimeAlarm (0x02) 16 bits minutes

Remaining capacity alarm 0x04/0x05 Sets RemainingCapacityAlarm (0x01) 16 bits mAh

Reserved 0x06/0x07 Reserved for future use 16 bits NA

Initial charging current 0x08/0x09 Sets the initial charging current 16 bits mA

Charging voltage 0x0a/0x0b Sets ChargingVoltage (0x15) 16 bits mV

Battery status 0x0c/0x0d Initializes BatteryStatus (0x16) 16 bits NA

Cycle count 0x0e/0x0f Initializes and stores CycleCount (0x17) 16 bits cycles

Design capacity 0x10/0x11 Sets DesignCapacity (0x18) 16 bits mAh

Design voltage 0x12/0x13 Sets DesignVoltage (0x19) 16 bits mV

Specification information 0x14/0x15 Programs SpecificationInfo (0x1a) 16 bits NA

Manufacture date 0x16/0x17 Programs ManufactureDate (0x1b) 16 bits NA

Serial number 0x18/0x19 Programs SerialNumber (0x1c) 16 bits NA

Fast-charging current 0x1a/0x1b Sets ChargingCurrent (0x14) 16 bits mA

Maintenance-charge current 0x1c/0x1d Sets the trickle current request 16 bits mA

Reserved 0x1e/0x1f Reserved must = 0x0000 16 bits mAh

Manufacturer name 0x20-0x2b Programs ManufacturerName (0x20) 96 bits NA

Current overload 0x2c/0x2d Sets the overload current threshold 16 bits mA

Battery low % 0x2e Sets the battery low amount 8 bits %

Reserved 0x2f Reserved for future use 8 bits NA

Device name 0x30-0x37 Programs DeviceName (0x21) 64 bits NA

Li-Ion taper current 0x38/0x39 Sets the upper limit of the taper current for charge

termination 16 bits mA

Maximum overcharge limit 0x3a/0x3b Sets the maximum amount of overcharge 16 bits NA

Reserved 0x3c Reserved must = 0x00 8 bits NA

Access protect 0x3d Locks commands outside of the SBS data set 8 bits NA

FLAGS1 0x3e Initializes FLAGS1 8 bits NA

FLAGS2 0x3f Initializes FLAGS2 8 bits NA

Device chemistry 0x40-0x45 Programs DeviceChemistry (0x22) 48 bits NA

Current measurement gain 0x46/0x47 Sense resistor calibration value 16 bits NA

Battery voltage offset 0x48 Voltage calibration value 8 bits NA

Temperature offset 0x49 Temperature calibration value 8 bits NA

Maximum temperature and

∆T step 0x4a Sets the maximum charge temperature and the ∆T

step for ∆T/∆t termination 8 bits NA

Table 1. Configuration Memory Map

bq2040

Parameter Name Address Description Length Units

Charge efficiency 0x4b Sets the high/low charge rate efficiencies 8 bits NA

Full charge percentage 0x4c Sets the percent at which the battery is consid-

ered fully charged 8 bits NA

Digitial filter 0x4d Sets the minimum charge/discharge threshold 8 bits NA

Current integration gain 0x4e Programs the current integration gain to the

sense resistor value 8 bits NA

Self-discharge rate 0x4f Sets the battery’s self-discharge rate 8 bits NA

Manufacturer data 0x50-0x55 Programs ManufacturerData (0x23) 48 bits NA

Voltage gain1 0x56/0x57 Battery divider calibration value 16 bits NA

Reserved 0x58-0x59 Reserved 16 bits NA

EDVF charging current 0x5a/0x5b Sets the charge current request when the battery

voltage is less than EDVF 16 bits NA

End of discharge voltage1 0x5c/0x5d Sets EDV1 16 bits NA

End of discharge voltage final 0x5e/0x5f Sets EDVF 16 bits NA

Full-charge capacity 0x60/0x61 Initializes and stores FullChargeCapacity (0x10) 16 bits mAh

∆t step 0x62 Sets the ∆t step for ∆T/∆t termination 8 bits NA

Hold-off time 0x63 Sets ∆T/∆t hold-off timer 8 bits NA

EEPROM check 2 0x64 EEPROM data integrity check byte

must = 0xb5 8 bits NA

Reserved 0x65-0x7f Reserved for future use NA

Table 1. Configuration Memory Map (Continued)

Voltage Thresholds

In conjunction with monitoring VSR for charge/discharge

currents, the bq2040 monitors the battery potential

through the SB pin. The voltage potential is deter-

mined through a resistor-divider network per the fol-

lowing equation:

MBV

2.25

1=−

where MBV is the maximum battery voltage, R5is con-

nected to the positive battery terminal, and R4is con-

nected to the negative battery terminal. R5/R4should be

rounded to the next higher integer. The voltage at the

SB pin (VSB) should never exceed 2.4V.

The battery voltage is monitored for the end-of-

discharge voltages (EDV1 and EDVF) and for alarm

warning conditions. EDV threshold levels are used to de-

termine when the battery has reached a programmable

“empty” state. The bq2040 generates an alarm warning

when the battery voltage exceeds the maximum charg-

ing voltage by 5% or if the voltage is below EDVF. The

battery voltage gain, the two EDV thresholds, and the

charging voltage are programmable in the EEPROM.

If VSB is below either of the two EDV thresholds, the associ-

ated flag is latched and remains latched, independent of

VSB, until the next valid charge.

EDV monitoring may be disabled under certain condi-

tions. If the discharge current is greater than the value

stored in location 0x2c and 0x2d in the EEPROM (EE

0x2c/0x2d), EDV monitoring is disabled and resumes af-

ter the current falls below the programmed value.

Reset

The bq2040 is reset when first connected to the battery

pack. On power-up, the bq2040 initializes and reads the

EEPROM configuration memory. The bq2040 can also

be reset with a command over the SMBus. The software

reset sequence is the following: (1) write MaxError

(0x0c) to 0x0000; (2) write the reset register (0x64) to

0x8009. A software reset can only be performed if the

bq2040 is in an unlocked state as defined by the value in

location 0x3d of the EEPROM (EE 0x3d) on power-up.

Temperature

The bq2040 monitors temperature sensing using an in-

ternal sensor. The temperature is used to adapt charge

and self-discharge compensations as well as to monitor

for maximum temperature and ∆T/∆t during a bq2040

controlled charge. Temperature may also be accessed

over the SMBus with command 0x08.

Layout Considerations

The bq2040 measures the voltage differential between

the SR and VSS pins. VOS (the offset voltage at the SR

pin) is greatly affected by PC board layout. For optimal

results, the PC board layout should follow the strict rule

of a single-point ground return. Sharing high-current

ground with small signal ground causes undesirable

noise on the small signal nodes. Additionally, in refer-

ence to Figure 1:

nThe capacitors (C1 and C2) should be placed as close as

possible to the SB and VCC pins, and their paths to VSS

should be as short as possible. A high-quality ceramic

capacitor of 0.1µf is recommended for VCC.

nThe sense resistor capacitor (C3) should be placed as

close as possible to the SR pin.

nThe bq2040 should be in thermal contact with the

cells for optimum temperature measurement.

Gas Gauge Operation

The operational overview diagram in Figure 2 illus-

trates the operation of the bq2040. The bq2040 accumu-

lates a measure of charge and discharge currents, as

well as an estimation of self-discharge. Charge currents

are compensated for temperature and state-of-charge of

the battery. Self-discharge is temperature-compensated.

The main counter, RemainingCapacity (RM), represents

the available battery capacity at any given time. Battery

charging increments the RM register, whereas battery dis-

charging and self-discharge decrement the RM register

and increment the internal Discharge Count Register

(DCR).

The Discharge Count Register is used to update the

FullChargeCapacity (FCC) register only if a complete

battery discharge from full to empty occurs without any

partial battery charges. Therefore, the bq2040 adapts

its capacity determination based on the actual condi-

tions of discharge.

The battery's initial full capacity is set to the value stored

in EE 0x60-0x61. Until FCC is updated, RM counts up to,

but not beyond, this threshold during subsequent charges.

The battery’s empty state is also programmed in the

EEPROM. The battery low percentage (EE 0x2e) stores

the percentage of FCC that will be written to RM when

the battery voltage drops below the EDV1 threshold.

1. FullChargeCapacity or learned-battery

capacity:

FCC is the last measured discharge capacity of the

battery. On initialization (application of VCC or reset),

FCC is set to the value stored in the EEPROM. Dur-

bq2040

ing subsequent discharges, FCC is updated with the

latest measured capacity in the Discharge Count Reg-

ister plus the battery low amount, representing a dis-

charge from full to below EDV1. A qualified dis-

charge is necessary for a capacity transfer from the

DCR to the FCC register. Once updated, the bq2040

writes the new FCC to the EEPROM. The FCC also

serves as the 100% reference threshold used by the

relative state-of-charge calculation and display.

2. DesignCapacity (DC):

The DC is the user-specified battery capacity and is

programmed from external EEPROM. The DC also

provides the 100% reference for the absolute dis-

play mode.

3. RemainingCapacity (RM):

RM counts up during charge to a maximum value of

FCC and down during discharge and self-discharge to

0. RM is set to the battery low amount after the

EDV1 threshold has been reached. If RM is already

equal to or less than the battery low amount, RM is

not modified. If RM reaches the battery low amount

before the battery voltage falls below EDV1 on dis-

charge, RM stops counting down until the EDV1

threshold is reached. RM is set to 0 when the battery

voltage reaches EDVF. To prevent overstatement of

charge during periods of overcharge, RM stops in-

crementing when RM = FCC. RM may optionally

be written to a user-defined value when fully

charged if the battery pack is under bq2040 charge

control. On initialization, RM is set to 0.

4. Discharge Count Register (DCR):

The DCR counts up during discharge independent

of RM and can continue increasing after RM has

decremented to 0. Prior to RM = 0, both discharge

and self-discharge increment the DCR. After RM

= 0, only discharge increments the DCR. The DCR

resets to 0 when RM = FCC and stops counting at

EDV1 on discharge. The DCR does not roll over but

stops counting when it reaches FFFFh.

FCC is updated on the first charge after a qualified

discharge to EDV1. The updated FCC equals the

battery low percentage times the current FCC plus

the DCR value. A qualified discharge to EDV1 oc-

curs if all of the following conditions exist:

nNo valid charge initiations (charges greater than

10mAh, where VSRO >+V

SRD occurred during

the period between RM = FCC and EDV1 de-

tected.

nThe self-discharge count is not more than

256mAh.

nThe low temperature fault bit in FLAGS2 is not

set when the EDV1 level is reached during dis-

charge.

nBattery voltage is not more than 256mV below

the EDV1 threshold when EDV1 is set.

The valid discharge flag (VDQ) in FLAGS1 indi-

cates whether the present discharge is valid for an

FCC update. FCC cannot be reduced by more than

256mAh during any single cycle.

bq2040

FG294501.eps

Temperature

Compensation

Charge

Current Discharge

Current Self-Discharge

Timer

Remaining

Capacity

(RM)

Full

Charge

Capacity

(FCC)

Discharge

Count

(DCR)

Qualified

Transfer

Temperature, Other Data

-- +

Inputs

Main Counters

and Capacity

Reference (FCC)

Outputs Two-Wire

Serial Interface

Chip-Controlled

Available Charge

LED Display

State-of-charge

and

Temperature

Compensation

Figure 2. Operational Overview

Charge Counting

Charge activity is detected based on a positive voltage

on the SR input. If charge activity is detected, the

bq2040 increments RM at a rate proportional to VSRO

and, if enabled, activates an LED display. Charge ac-

tions increment the RM after compensation for charge

state and temperature.

The bq2040 determines charge activity sustained at a

continuous rate equivalent to VSRO >+V

SRD.A valid

charge equates to sustained charge activity

greater than 10 mAh. Once a valid charge is detected,

charge threshold counting continues until VSRO falls be-

low VSRD.V

SRD is a programmable threshold as de-

scribed in the Digital Magnitude Filter section.

Discharge Counting

All discharge counts where VSRO <-V

SRD cause the RM

is a programmable threshold as described in the Digital

Magnitude Filter section.

Self-Discharge Estimation

The bq2040 continuously decrements RM and incre-

ments DCR for self-discharge based on time and temper-

ature provided that the discharge flag in BatteryStatus

is set (charge not detected). The bq2040 self-discharge

estimation rate is programmed in EE 0x4f and can be

set from 0 to 25% per day for 20–30°C. This rate approx-

imately doubles for every 10°C increase until the tem-

perature is ≥70°C or halves every 10°C decrease until

the temperature is < 10°C.

Charge Control

The bq2040 supports SBS charge control by broadcast-

ing the ChargingCurrent and the ChargingVoltage to

the Smart Charger address. The bq2040 broadcasts

charging commands every 10 seconds; the broadcasts

can be disabled by writing bit 14 of BatteryMode to 1.

On reset, the initial charging current broadcast to the

charger is set to the value programmed in EE 0x08-

0x09. The bq2040 updates the value used in the charg-

ing current broadcasts based on the battery’s state of

charge, voltage, and temperature.

The bq2040 internal charge control is compatible with

nickel-based and Li-Ion chemistries. The bq2040 uses

current taper detection for Li-Ion primary charge termi-

nation and ∆T/∆t for nickel based primary charge termi-

nation. The bq2040 also provides a number of safety

terminations based on battery capacity, voltage, and

temperature.

Current Taper

For Li-Ion charge control, the ChargingVoltage must be

set to the desired pack voltage during the constant volt-

age charge phase. The bq2040 detects a current taper

termination when it measures the pack voltage to be

within 128mV of the requested charging voltage and

when the AverageCurrent is less than the programmed

threshold in EE 0x38—0x39 and non-zero for at least

100s.

∆T/∆t

The ∆T/∆t used by the bq2040 is programmable in both

the temperature step (1.6°C–4.6°C) and time step (20

seconds–320seconds). Typical settings for 1°C/min in-

clude 2°C over 120 seconds and 3°C over 180 seconds.

Longer times are required for increased slope resolution.

∆

∆T

tis set by the formula: ∆

∆T

[]

[(

(lower nibble of EE 0x4a) 2 + 16 / 10

EE 0x62

∗

−320 ) 20)]

s∗









In addition to the ∆T/∆t timer, there is a hold-off timer,

which starts when the battery is being charged at more

than 255mA and the temperature is above 25°C. Until

this timer expires, ∆T/∆t is suspended. If the tempera-

ture falls below 25°C, or if charging current falls below

255mA, the timer is reset and restarts only if these con-

ditions are once again within range. The hold-off time is

programmed in EE 0x63.

Charge Termination

Once the bq2040 detects a valid charge termination, the

Fully_Charged, Terminate_Charge_Alarm, and the

Over_Charged_Alarm bits are set in BatteryStatus, and

the requested charge current is set to zero. Once the

terminating conditions cease, the Termi-

nate_Charge_Alarm and the Over_Charged_Alarm are

cleared, and the requested charging current is set to the

maintenance rate. The bq2040 requests the mainte-

nance rate until RM falls below the amount determined

by the programmable full- charge percentage. Once this

occurs, the Fully_Charged bit is cleared, and the re-

quested charge current and voltage are set to the

fast-charge rate.

Bit 4 (CC) in FLAGS2 determines whether RM is modi-

fied after a ∆T/∆t or current taper termination occurs. If

CC = 1, RM may be set from 0 to 100% of the FullChar-

geCapacity as defined in EE 0x4c. If RM is below the

full-charge percentage, RM is set to the full-charge per-

centage of FCC. If RM is above the full-charge percent-

age, RM is not modified.

bq2040

Charge Suspension

The bq2040 may temporarily suspend charge if it detects

a charging fault. The charging faults include the follow-

ing conditions:

Maximum Overcharge: If charging continues for

more than the programmed maximum overcharge

limit as defined in EE 0x3a—0x3b beyond RM=FCC,

the Fully_Charged bit is set, and the requested

charging current is set to the maintenance rate.

Overvoltage: An over-voltage fault exists when the

bq2040 measures a voltage more than 5% above the

ChargingVoltage. When the bq2040 detects an

overvoltage condition, the requested charge current is

set to 0 and the Terminate_Charge_Alarm bit is set

in BatteryStatus. The alarm bit is cleared when the

current drops below 256mA and the voltage is less

than 105% of ChargingVoltage.

Overcurrent: An overcurrent fault exists when the

bq2040 measures a charge current more than 25%

above the ChargingCurrent. If the ChargingCurrent

is less than 1024mA, an overcurrent fault exists if the

charge current is more than 1mA above the lowest

multiple of 256mA that exceeds the ChargingCurrent.

When the bq2040 detects an overcurrent condition, the

requested charge current is set to 0 and the

Terminate_Charge_Alarm bit is set in Battery Status.

The alarm bit is cleared when the current drops below

256mA.

Maximum Temperature: When the battery

temperature equals the programmed maximum

temperature, the requested charge current is set to

zero and the Over_Temp_Alarm and the

Terminate_Charge_Alarm bits are set in Battery

Status. The Over_Temp_Alarm bit is cleared when

the temperature drops to 43°C below the maximum

temperature threshold minus 5°C.

PSTAT: When the PSTAT input is ≥1.5V, the

requested charge current is set to 0 and the

Terminate_Charge_Alarm bit is set in BatteryStatus

if the Discharging flag is not set. The alarm bit is

cleared when the PSTAT input is <1.0V or the

Discharging flag is set.

Low Temperature: When the battery temperature

is less than 12°C (LTF bit in FLAGS2 set), the

requested charge current is set to the maintenance

rate. Once the temperature is above 15°C, the

requested charge current is set to the fast rate.

Undervoltage: When the battery voltage is below

the EDVF threshold, the requested charge current is

set to the EDVF rate stored in EE0x5a/0x5b. Once

the voltage is above EDVF, the requested charge

current is set to the fast or maintenance rate

depending on the state of the LTF bit.

Count Compensations

Charge activity is compensated for temperature and

state-of-charge before updating the RM and/or DCR.

Self-discharge estimation is compensated for tempera-

ture before updating RM or DCR.

Charge Compensation

Charge efficiency is compensated for state-of-charge,

temperature, and battery chemistry. The charge effi-

ciency is adjusted using the following equations:

1.) RM RM * Q Q

EFC ET

=−()

where RelativeStateOfCharge < FullChargePercentage,

and QEFC is the programmed fast-charge efficiency vary-

ing from 0.75 to 1.0.

2.) RM RM Q Q

ETC ET

=−*( )

where RelativeStateOfCharge ≥FullChargePercentage

and QETC is the programmed maintenance (trickle)

charge efficiency varying from 0.75 to 1.0.

QET is used to adjust the charge efficiency as the battery

temperature increases according to the following:

QifT

ET =<030

°C

QCTC

ET =°≤<°002 30 40.if

QTC

ET =≥°005 40.if

QET is 0 over the entire temperature range for Li-Ion.

Digital Magnitude Filter

The bq2040 has a programmable digital filter to elimi-

nate charge and discharge counting below a set

threshold, VSRD. Table 2 shows typical digital filter

settings. The proper digital filter setting can be calcu-

lated using the following equation.

DMF = 45

VSRD

bq2040

DMF DMF Hex. VSRD (mV)

75 4B 0.60

100 64 0.45

150 96 0.30

175 AF 0.26

200 C8 0.23

Table 2. Typical Digital Filter Settings

Error Summary

Capacity Inaccurate

The FCC is susceptible to error on initialization or if no

updates occur. On initialization, the FCC value includes

the error between the design capacity and the actual ca-

pacity. This error is present until a qualified discharge

occurs and FCC is updated (see the DCR description).

The other cause of FCC error is battery wear-out. As the

battery ages, the measured capacity must be adjusted to

account for changes in actual battery capacity. Periodic

qualified discharges from full to empty will minimize er-

rors in FCC.

Current-Sensing Error

Table 3 illustrates the current-sensing error as a func-

tion of VSR. A digital filter eliminates charge and dis-

charge counts to the RM register when -VSRD <V

SRO <

SRD.

Display

The bq2040 can directly display capacity information us-

ing low-power LEDs. The bq2040 displays the battery

charge state in either absolute or relative mode. In rela-

tive mode, the battery charge is represented as a per-

centage of the FCC. Each LED segment represents 25%

of the FCC.

In absolute mode, each segment represents a fixed

amount of charge, 25% of the DesignCapacity. As the

battery wears out over time, it is possible for the FCC to

be below the design capacity. In this case, all of the

LEDs may not turn on in absolute mode, representing

the reduction in the actual battery capacity.

When DISP is tied to VCC, the LED1-4 outputs are inac-

tive. When DISP is left floating, the display becomes ac-

tive whenever the bq2040 detects a charge rate of

100mA or more. When pulled low, the segment outputs

become active immediately for a period of approximately

4 seconds. The DISP pin must be returned to float or

VCC to reactivate the display.

LED1blinks at a 4Hz rate indicating a low battery con-

dition whenever the display is active, EDVF is not set,

and Remaining_Capacity_Alarm is set. VSB below EDVF

(EDVF = 1) disables the display output.

Microregulator

The bq2040 can operate directly from three nickel chem-

istry cells. To facilitate the power supply requirements

of the bq2040, an REF output is provided to regulate an

external low-threshold n-FET. A micropower source for

the bq2040 can be built inexpensively using a 2N7002 or

BSS138 FET and an external resistor. (See Figure 1.)

The value of R11 depends on the battery pack’s nominal

voltage.

Communicating With the bq2040

The bq2040 includes a simple two-pin (SMBC and

SMBD) bi-directional serial data interface. A host proc-

essor uses the interface to access various bq2040 regis-

ters; see Table 4. This method allows battery character-

istics to be monitored easily. The open-drain SMBD and

SMBC pins on the bq2040 are pulled up by the host sys-

tem, or may be connected to VSS, if the serial interface is

not used.

The interface uses a command-based protocol, where the

host processor sends the battery address and an eight-

bit command byte to the bq2040. The command directs

the bq2040 to either store the next data received to a

data specified by the command byte.

bq2040 Data Protocols

The host system, acting in the role of a Bus master, uses

the read word and write word protocols to communicate

integer data with the bq2040. (See Figure 3).

Host-to-bq2040 Message Protocol

The Bus Host communicates with the bq2040 using one

of three protocols:

nRead word

nWrite word

bq2040

Symbol Parameter Typical Maximum Units Notes

VOS Offset referred to VSR ±75 ±150 µV DISP = VCC.

INL Integrated non-linearity

error ±1±4%Add 0.1% per °C above or below 25°C

and 1% per volt above or below 4.25V.

INR Integrated non-

repeatability error ±0.5 ±1%Measurement repeatability given

similar operating conditions.

Table 3. bq2040 Current-Sensing Errors

nRead block

The particular protocol used is a function of the com-

mand. The protocols used are shown in Figure 3.

Host-to-bq2040 Messages (see Table 4)

ManufacturerAccess() (0x00)

This read/write word is an open location.

Input/Output: word.

RemainingCapacityAlarm() (0x01)

This function sets or returns the low-capacity alarm

value. When RM falls below the RemainingCapac-

ityAlarm value initialized from the external EE-

PROM, the Remaining_Capacity_Alarm bit is set in

BatteryStatus. The system may alter this alarm dur-

ing operation.

Input/Output: unsigned integer. This sets/returns

the value where the Remaining_Capacity_Alarm

bit is set in Battery Status.

Units: mAh

Range: 0 to 65,535mAh

RemainingTimeAlarm() (0x02)

This function sets or returns the low remaining time

alarm value. When the AverageTimeToEmpty falls be-

low this value, the Remaining_Time_Alarm bit in Bat-

teryStatus is set. The default value for this register is

programmed in EE 0x02-0x03.. The system may alter

this alarm during operation.

Input/Output: unsigned integer. This sets/returns

the value where the Remaining_Time_Alarm bit is

set in Battery Status.

Units: minutes

Range: 0 to 65,535 minutes

BatteryMode() (0x03)

This read/write word selects the various battery opera-

tional modes. The bq2040 supports the battery capacity

information specified in mAh. This function also deter-

mines whether the bq2040 charging values are broad-

casted to the Smart Battery Charger address.

Writing bit 14 to 1 disables voltage and current Master

Mode broadcasts to the Smart Battery Charger. Bit 14 is

automatically reset to 0 if SMBC and SMBD = 0 for

greater than 2 seconds (i.e. pack removal).

Writing bit 13 to 1 disables all Master Mode broadcasts

including alarm messages to the Smart Battery Charger

and Host. The bit remains set until overwritten. Pro-

gramming bit 3 of FLAGS2 in the EEPROM (EE0x3f)

initializes this bit to a 1.

Bit 7 is the condition request flag. It is set when the

bq2040 is initialized from the EEPROM and reset when a

learning cycle has been completed. It is also set toa1if

CycleCount increases by 32 without a new learning cycle.

AtRate() (0x04)

This read/write word is the first half of a two-function

set used to set the AtRate value used in calculations

made by the AtRateTimeToFull and AtRateTime-

ToEmpty.

bq2040

FG204001.eps

SBattery Address

0001011 0A Command Code A Data byte low A Data byte high AP

11818181171

SBattery Address

0001011 0A Command Code A Battery Address A1

117181171

1818

PData byte low Data byte high

SBattery Address

0001011

0A Command Code A Battery Address A1

117181171

1818

Byte Count =N Data byte 1 AA

1818

PData byte 2 Data byte N

bq2040

System Host

Block Read

Read Word

Write Word

A – ACKNOWLEDGE

A – NOT ACKNOWLEDGE

S – START

P – STOP

Figure 3. Host Communication Protocols

bq2040

Function Code Access Units Defaults1

ManufacturerAccess 0x00 read/write - -

RemaningCapacityAlarm 0x01 read/write mAh E2

RemainingTimeAlarm 0x02 read/write minutes E2

BatteryMode 0x03 read/write bit flag -

AtRate 0x04 read/write mA -

AtRateTimeToFull 0x05 read minutes -

AtRateTimeToEmpty 0x06 read minutes -

AtRateOK 0x07 read Boolean -

Temperature 0x08 read 0.1°K 2930

Voltage 0x09 read mV E2

Current 0x0a read mA 0

AverageCurrent 0x0b read mA 0

MaxError 0x0c read percent 100

RelativeStateOfCharge 0x0d read percent -

AbsoluteStateOfCharge 0x0e read percent -

RemainingCapacity 0x0f read mAh E2

FullChargeCapacity 0x10 read mAh E2

RunTimeToEmpty 0x11 read minutes -

AverageTimeToEmpty 0x12 read minutes -

AverageTimeToFull 0x13 read minutes -

ChargingCurrent 0x14 read mA E2

ChargingVoltage 0x15 read mV E2

Battery Status 0x16 read bit flags E2

CycleCount 0x17 read cycle E2

DesignCapacity 0x18 read mAh E2

DesignVoltage 0x19 read mV E2

SpecificationInfo 0x1a read - E2

ManufactureDate 0x1b read - E2

SerialNumber 0x1c read integer E2

Reserved 0x1d - 0x1f - - -

ManufacturerName 0x20 read string E2

DeviceName 0x21 read string E2

Note: 1. Defaults after reset or power-up.

Table 4. bq2040 Register Functions

bq2040

Function Code Access Units Defaults1

DeviceChemistry 0x22 read string E2

ManufacturerData 0x23 read string E2

FLAG1 and FLAG2 0x2f read bit flags E2

End of Discharge Voltage 1 (EDV1) 0x3e read - E2

End of Discharge Voltage Final

(EDVF) 0x3f read - E2

Note: 1. Defaults after reset or power-up.

Table 4. bq2040 Register Functions (Continued)

nWhen the AtRate value is positive, the

AtRateTimeToFull function returns the predicted

time to full-charge at the AtRate value of charge.

nWhen the AtRate value is negative, the

AtRateTimeToEmpty function returns the predicted

operating time at the AtRate value of discharge.

Input/Output: signed integer. AtRate is positive

for charge and negative for discharge.

Units: mA

Range: -32,768mA to 32,767mA

AtRateTimeToFull() (0x05)

This read-only word returns the predicted remaining

time to fully charge the battery at the AtRate value

(mA) and is valid only if read immediately after an

AtRate command.

Output: unsigned integer. Returns the predicted

time to full charge.

Units: minutes

Range: 0 to 65,534min

Granularity: 2 min or better

Invalid Data Indication: 65,535 indicates that the

AtRate value is negative.

AtRateTimeToEmpty() (0x06)

This read-only word returns the predicted remaining op-

erating time if the battery is discharged at the AtRate

value and is valid only if read immediately after an

AtRate command.

Output: unsigned integer. Returns the predicted

time to empty.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Invalid Data Indication: 65,535 indicates that the

AtRate value is not negative.

AtRateOK() (0x07)

This read-only word returns a Boolean value that indi-

cates whether or not the EDVF flag has been set.

Boolean: Indicates if the battery can supply addi-

tional energy.

Units: Boolean

Range: TRUE ≠0, FALSE = 0

Temperature() (0x08)

This read-only word returns the cell-pack's internal

temperature.

Output: unsigned integer. Returns the cell tem-

perature in tenths of degrees Kelvin increments.

Units: 0.1°K

Range: 0 to +500.0°K

Granularity: 0.5°K or better

Accuracy: ±3°K after calibration

Voltage() (0x09)

This read-only word returns the cell-pack voltage (mV).

Output: unsigned integer. Returns the battery ter-

minal voltage in mV.

Units: mV

Range: 0 to 65,535mV

Granularity: 0.2% of DesignVoltage

Accuracy: ±1% of DesignVoltage after calibration

Current() (0x0a)

This read-only word returns the current through the

battery's terminals (mA).

Output: signed integer. Returns the charge/dis-

charge rate in mA, where positive is for charge

and negative is for discharge

Units: mA

Range: 0 to 32,767mA for charge or 0 to

–32,768mA for discharge

Granularity: 0.2% of the DesignCapacity or better

Accuracy: ±1% of the DesignCapacity after calibration

AverageCurrent() (0x0b)

This read-only word returns a rolling average of the cur-

rent through the battery's terminals. The AverageCur-

rent function returns meaningful values after the bat-

tery's first minute of operation.

Output: signed integer. Returns the charge/dis-

charge rate in mA, where positive is for charge

and negative is for discharge

Units: mA

Range: 0 to 32,767mA for charge or 0 to

–32,768mA for discharge

Granularity: 0.2% of the DesignCapacity or better

bq2040

Accuracy: ±1% of the DesignCapacity after cali-

bration

MaxError() (0x0c)

Returns the expected margin of error (%) in the state of

charge calculation.

Output: unsigned integer. Returns the percent un-

certainty for selected information.

Units: %

Range: 0 to 100%

RelativeStateOfCharge() (0x0d)

This read-only word returns the predicted remaining

battery capacity expressed as a percentage of FullChar-

geCapacity (%). RelativeStateOfCharge is only

valid for battery capacities more than 1504mAh

and less than 10,400mAh.

Output: unsigned integer. Returns the percent of re-

maining capacity.

Units: %

Range: 0 to 100%

Granularity: 1%

Accuracy: ±MaxError after circuit and capacity

calibration

AbsoluteStateOfCharge() (0x0e)

This read-only word returns the predicted remaining

battery capacity expressed as a percentage of DesignCa-

pacity (%). Note that AbsoluteStateOfCharge can return

values greater than 100%. Absolute StateOfCharge

is only valid for battery capacities more than

1504mAh and less than 10,400mAh.

Output: unsigned integer. Returns the percent of

remaining capacity.

Units: %

Range: 0 to 65,535%

Granularity: 1%

Accuracy: ±MaxError after circuit and capacity

calibration

RemainingCapacity() (0x0f)

This read-only word returns the predicted remaining

battery capacity. The RemainingCapacity value is ex-

pressed in mAh.

Output: unsigned integer. Returns the estimated re-

maining capacity in mAh.

Units: mAh

Range: 0 to 65,535mAh

Granularity: 0.2% of DesignCapacity or better

Accuracy: ±MaxError ∗FCC after circuit and ca-

pacity calibration

FullChargeCapacity() (0x10)

This read-only word returns the predicted pack capacity

when it is fully charged. FullChargeCapacity defaults

to the value programmed in the external EEPROM until

a new pack capacity is learned. The new FCC is stored

to EEPROM within 400ms of a valid charge after a

qualified discharge.

Output: unsigned integer. Returns the estimated full

charge capacity in mAh.

Units: mAh

Range: 0 to 65,535mAh

Granularity: 0.2% of DesignCapacity or better

Accuracy: ±MaxError ∗FCC after circuit and ca-

pacity calibration

RunTimeToEmpty() (0x11)

This read-only word returns the predicted remaining

battery life at the present rate of discharge (minutes).

The RunTimeToEmpty value is calculated based on

Current.

Output: unsigned integer. Returns the minutes of

operation left.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Invalid data indication: 65,535 indicates battery is

not being discharged.

AverageTimeToEmpty() (0x12)

This read-only word returns the predicted remaining

battery life at the present average discharge rate (min-

utes). The AverageTimeToEmpty is calculated based on

AverageCurrent.

bq2040

Output: unsigned integer. Returns the minutes of

operation left.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Invalid data indication: 65,535 indicates battery

is not being discharged.

AverageTimeToFull() (0x13)

This read-only word returns the predicted time until the

Smart Battery reaches full charge at the present aver-

age charge rate (minutes).

Output: unsigned integer. Returns the remaining

time in minutes to full.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Invalid data indication: 65,535 indicates battery

is not being charged.

ChargingCurrent() (0x14)

If enabled, the bq2040 sends the desired charging rate in

mA to the Smart Battery Charger.

Output: unsigned integer. Transmits/returns the

maximum charger output current in mA.

Units: mA

Range: 0 to 65,534mA

Granularity: 0.2% of the design capacity or better

Invalid data indication: 65,535 indicates that the

Smart Charger should operate as a voltage source

outside its maximum regulated current range.

ChargingVoltage() (0x15)

If enabled, the bq2040 sends the desired voltage in mV

to the Smart Battery Charger.

Output: unsigned integer. Transmits/returns the

charger voltage output in mV.

Units: mV

Range: 0 to 65,534mV

Granularity: 0.2% of the DesignVoltage or better

Invalid data indication: 65,535 indicates that the

Smart Battery Charger should operate as a cur-

rent source outside its maximum regulated voltage

range.

BatteryStatus() (0x16)

This read-only word returns the battery status word.

Output: unsigned integer. Returns the status reg-

ister with alarm conditions bitmapped as shown in

Table 5.

Some of the BatteryStatus flags (Remaining_Capac-

ity_Alarm and Remaining_Time_Alarm) are calculated

based on current. See Table 8 and 9 for definitions.

CycleCount() (0x17)

This read-only word returns the number of charge/dis-

charge cycles the battery has experienced. A charge/dis-

charge cycle starts from a base value equivalent to the

battery's state-of-charge on completion of a charge cycle.

The bq2040 increments the cycle counter during the cur-

rent charge cycle if the battery has been discharged 15%

below the state-of-charge at the end of the last charge cy-

cle. This prevents false reporting of small charge/discharge

cycles. The cycle count is stored in EEPROM within

400ms of an update.

Output: unsigned integer. Returns the count of

charge/discharge cycles the battery has

experienced.

Units: cycles

bq2040

Alarm Bits

0x8000 Over_Charged_Alarm

0x4000 Terminate_Charge_Alarm

0x2000 Reserved

0x1000 Over_Temp_Alarm

0x0800 Terminate_Discharge_Alarm

0x0400 Reserved

0x0200 Remaining_Capacity_Alarm

0x0100 Remaining_Time_Alarm

Status Bits

0x0080 Initialized

0x0040 Discharging

0x0020 Fully_Charged

0x0010 Fully_Discharged

Error Code

0x0000-

0x000f Reserved for error codes

Table 5. Status Register

Range: 0 to 65,535 cycles; 65,535 indicates battery

has experienced 65,535 or more cycles.

Granularity: 1 cycle

DesignCapacity() (0x18)

This read-only word returns the theoretical capacity of a

new pack. The DesignCapacity value is expressed in

mAh at the nominal discharge rate.

Output: unsigned integer. Returns the battery ca-

pacity in mAh.

Units: mAh

Range: 0 to 65,535mAh

DesignVoltage() (0x19)

This read-only word returns the theoretical voltage of

a new pack in mV.

Output: unsigned integer. Returns the battery's

normal terminal voltage in mV.

Units: mV

Range: 0 to 65,535mV

SpecificationInfo() (0x1a)

This read-only word returns the specification re-

vision the bq2040 supports.

ManufactureDate() (0x1b)

This read-only word returns the date the cell was manu-

factured in a packed integer word. The date is packed

as follows: (year - 1980) ∗512 + month ∗32+day.

SerialNumber() (0x1c)

This read-only word returns a serial number. This

number, when combined with the ManufacturerName,

the DeviceName, and the ManufactureDate, uniquely

identifies the battery.

Output: unsigned integer

ManufacturerName() (0x20)

This read-only string returns a character string where the

first byte is the number of characters available. The maxi-

mum number of characters is 11. The character string con-

tains the battery manufacturer's name. For example,

“Benchmarq” identifies the battery pack manufacturer as

Benchmarq.

Output: string or ASCII character string

DeviceName() (0x21)

This read-only string returns a character string where the

first byte is the number of characters available. The maxi-

mum number of characters is 7. The 7-byte character string

contains the battery's name. For example, a DeviceName of

“bq2040” indicates that the battery is a model bq2040.

Output: string or ASCII character string

DeviceChemistry() (0x22)

This read-only string returns a character string where

the first byte is the number of characters available. The

maximum number of characters is 5. The 5-byte charac-

ter string contains the battery's chemistry. For example,

if the DeviceChemistry function returns “NiMH,” the

battery pack contains nickel-metal hydride cells.

Output: string or ASCII character string

ManufacturerData() (0x23)

This read-only string allows access to an up to 5-byte

manufacturer data string.

Output: block data—data whose meaning is as-

signed by the Smart Battery's manufacturer.

bq2040

(MSB) 7 6543210 (LSB)

FLAGS2 DMODE PSTAT CHM CC - OV LTF OC

FLAGS1 ∆T/∆tIMIN VQ - VDQ OVLD EDV1 EDVF

Note: - = Reserved

Table 6. Bit Descriptions for FLAGS1 and FLAGS2

Field Bits

Used Format Allowable Value

Day 0–4 5-bit binary

value

1–31 (corresponds to

date)

Month 5–8 4-bit binary

value

1–12 (corresponds to

month number)

Year 9–15 7-bit binary

value

0–127 (corresponds to

year biased by 1980)

End of Discharge Voltage1 (0x3e)

This read-only word returns the first end-of-discharge

voltage programmed for the pack.

Output: two’s complemented unsigned integer.

Returns battery end-of-discharge voltage pro-

grammed in EEPROM in mV.

End of Discharge VoltageF (0x3f)

This read-only word returns the final end-of-discharge

voltage programmed for the pack.

Output: two’s complemented unsigned integer.

Returns battery final end-of-discharge voltage pro-

grammed in EEPROM in mV.

FLAGS1&2() (0x2f)

This read-only register returns an unsigned integer rep-

resenting the internal status registers of the bq2040.

The MSB represents FLAGS2, and the LSB represents

FLAGS1. See Table 6 for the bit description for FLAGS1

and FLAGS2.

FLAGS2

The Display Mode flag (DMODE), bit 7 determines

whether the bq2040 displays Relative or Absolute capac-

ity.

The DMODE value is:

Where DMODE is:

0 Selects Absolute display

1 Selects Relative display

Bit 6 reflects the high/low state of PSTAT. PSTAT ≥1.5V

generates a charge suspend condition.

The PSTAT value is:

Where PSTAT is:

0 PSTAT input < 1.0V

1 PSTAT input ≥1.5V

The Chemistry flag (CHM), bit 5, selects Li-Ion or nickel

compensation factors.

The CHM value is:

Where CHM is:

0 Selects Nickel

1 Selects Li-Ion

Bit 4, the Charge Control flag (CC), determines whether

a bq2040-based charge termination will set RM to a

user-defined programmable full charge capacity.

The CC value is:

Where CC is:

0 RM is not modified on valid bq2040

charge termination

1 RM is set to a programmable percentage of

the FCC when a valid bq2040 charge termi-

nation occurs

Bit 3 is reserved.

Bit 2, the Overvoltage flag (OV), is set when the bq2040

detects a pack voltage 5% greater than the programmed

charging voltage. This bit is cleared when the pack volt-

age falls 5% below the programmed charging voltage.

The OV value is:

Where OV is:

0 Voltage < 1.05 ∗ChargingVoltage

1 Voltage ≥1.05 ∗ChargingVoltage

Bit 1, the Low Temperature Fault flag (LTF), is set when

Temperature is < 12°C and cleared when Temperature

is ≥15°C.

The LTF value is:

bq2040

FLAGS2 Bits

76 5 43210

- - - - -OV- -

FLAGS2 Bits

76 5 43210

-- - CC----

FLAGS2 Bits

7 6543210

DMODE -------

FLAGS2 Bits

76 5 43210

--CHM-----

FLAGS2 Bits

76 5 43210

-- - ---LTF-

FLAGS2 Bits

7 6 543210

-PSTAT------

Where LTF is:

0 Temperature > 15°C

1 Temperature < 12°C

Bit 0, the Overcurrent flag (OC), is set when Current is

25% greater than the programmed charging current. If

the charging current is programmed less than 1024mA,

overcurrent is set if Current is 256mA greater than the

programmed charging current. This flag is cleared when

Current falls below 256mA.

The OC value is:

Where OC is:

0 Current is less than 1.25 ∗ChargingCur-

rent or less than 256mA if charging current

is programmed less than 1024mA

1 Current exceeds 1.25 ∗ChargingCurrent or

256mA if the charging current is pro-

grammed less than 1024mA. This bit is

cleared if Current < 256mA.

FLAGS1

Bits 7 indicates that a ∆T/∆t termination condition

exists.

The ∆T/∆t value is:

Where ∆T/∆t is:

0 The ∆T/∆t rate drops below the pro-

grammed rate.

1 The ∆T/∆t rate exceeds the programmed

rate.

Bit 6 indicates that a current taper termination condi-

tion exists.

The IMIN value is:

Where IMIN is:

0 A valid current taper termination condition

is not present.

1 Valid current taper termination condition

detected.

The Valid Charge flag (VQ), bit 5, is set when VSRO ≥

|VSRD| and 10mAh of charge has accumulated. This bit

is cleared during a discharge and when VSRO ≤|VSRD|.

The VQ value is:

Where VQ is:

SRO ≤|VSRD|

SRO ≥|VSRD| and 10mAh of charge has

accumulated

Bit 4 is reserved.

The Valid Discharge flag (VDQ), bit 3, is set when a

valid discharge is occurring (discharge cycle valid for

learning new full charge capacity) and cleared if a par-

tial charge is detected, EDV1 is asserted when T < 0°C,

or self-discharge accounts for more than 256mAh of the

discharge.

The VDQ value is:

Where VDQ is:

0 Self-discharge is greater than 256mAh,

EDV1 = 1 when T < 0°C or VQ = 1

1 On first discharge after RM=FCC

The Overload flag (OVLD), bit 2, is set when the dis-

charge current is greater than the programmed rate and

cleared when the discharge current falls below the pro-

grammed rate.

bq2040

FLAGS1 Bits

76543 2 10

- - - - - OVLD - -

FLAGS1 Bits

76 5 43210

-- VQ-----

FLAGS1 Bits

7654 3 210

- - - - VDQ - - -

FLAGS2 Bits

765432 1 0

------ -OC

FLAGS1 Bits

7 6 5 43210

∆T/∆t- - -----

FLAGS1 Bits

7 6 5 43210

-I

MIN - -----

The OVLD value is:

Where OVLD is:

0 Current < programmed rate

1 Current > programmed rate

The First End-of-Discharge Voltage flag (EDV1), bit 1, is

set when Voltage < EDV1 and OVLD = 0 and cleared

when VQ = 1 and Voltage > EDV1.

The EDV1 value is:

Where EDV1 is:

0 VQ = 1 and Voltage > EDV1

1 Voltage < EDV1 and OVLD = 0

The Final End-of-Discharge Voltage flag (EDVF), bit 0, is

set when Voltage < EDVF and OVLD = 0 and cleared

when VQ = 1 and Voltage > EDVF.

The EDVF value is:

Where EDVF is:

0 VQ = 1 and Voltage > EDVF

1 Voltage < EDVF and OVLD = 0

Error Codes and Status Bits

Error codes and status bits are listed in Table 8 and Ta-

ble 9, respectively.

SBD Seal

The bq2040 address space can be “locked” to enforce the

SBS specified access to each command code. To lock the

address space, the bq2040 must be initialized with EE

0x3d set to b0h. Once this is done, only commands

0x00-0x04 may be written. Attempting to write to any

other address will cause a “no acknowledge” of the data.

Reading will only be permitted from the command codes

listed in the SBD specification plus the five locations

designated as optional manufacturing functions 1–5

(0x2f, 0x3c–0x3f).

Programming the bq2040

The bq2040 requires the proper programming of an ex-

ternal EEPROM for proper device operation. Each mod-

ule can be calibrated for the greatest accuracy, or gen-

eral “default” values can be used. An EV2200-40 pro-

gramming kit (interface board, software, and cable) for

an IBM-compatible PC is available from Benchmarq.

The bq2040 uses a 24LC01 or equivalent serial EE-

PROM (capable of read operation to 2.0V) for storing the

various initial values, calibration data, and string infor-

mation. Table 1 outlines the parameters and addresses

for this information. Tables 10 and 11 detail the various

for an 2400mAh 4-series Li-Ion battery pack, using a

50mΩsense resistor.

bq2040

FLAGS1 Bits

765432 1 0

- - - - - - EDV1 -

FLAGS1 Bits

7654321 0

- - - - - - - EDVF

bq2040

Error Code Access Description

OK 0x0000 read/write bq2040 processed the function code without detecting any errors.

Busy 0x0001 read/write bq2040 is unable to process the function code at this time.

ReservedCommand 0x0002 read/write bq2040 cannot read or write the data at this time—try again

later.

UnsupportedCommand 0x0003 read/write bq2040 does not support the requested function code.

AccessDenied 0x0004 write bq2040 detected an attempt to write to a read-only function

code.

Overflow/Underflow 0x0005 read/write bq2040 detected a data overflow or underflow.

BadSize 0x0006 write bq2040 detected an attempt to write to a function code with an

incorrect size data block.

UnknownError 0x0007 read/write bq2040 detected an unidentifiable error.

Note: Reading the bq2040 after an error clears the error code.

Table 8. Error Codes (BatteryStatus() (0x16))

bq2040

Alarm Bits

Bit Name Set When: Reset When:

OVER_CHARGED_ALARM

The bq2040 detects a ∆T/∆t or cur-

rent taper termination. (Note:

∆T/∆t and current taper are valid

charge terminations.)

A discharge occurs or when the

∆T/∆t or current taper termination

condition ceases during charge.

TERMINATE_CHARGE_ALARM

The bq2040 detects an over-current,

over-voltage, over-temperature,

∆T/∆t, or current taper condition

during charge.

A discharge occurs or when all condi-

tions causing the event cease.

OVER_TEMP_ALARM

The bq2040 detects that its internal

temperature is greater than the pro-

grammed value.

Internal temperature falls to 43°C or

the maximum temperature threshold

minus 5°C.

TERMINATE_DISCHARGE_ALARM

The bq2040 determines that it has

supplied all the charge that it can

without being damaged (Voltage <

EDVF).

Voltage > EDVF signifies that the

battery has reached a state of charge

sufficient for it to once again safely

supply power.

REMAINING_CAPACITY_ALARM

The bq2040 detects that the Remain-

ingCapacity is less than that set by

the RemainingCapacityAlarm func-

tion.

Either the value set by the Remain-

ingCapacityAlarm function is lower

than the Remaining Capacity or the

RemainingCapacity is increased by

charging.

REMAINING_TIME_ALARM

The bq2040 detects that the esti-

mated remaining time at the present

discharge rate is less than that set

by the RemainingTimeAlarm func-

tion.

Either the value set by the Remain-

ingTimeAlarm function is lower than

the AverageTimeToEmpty or a valid

charge is detected.

Status Bits

Bit Name Set When: Reset When:

INITIALIZED The bq2040 loads from the EEPROM

(bit 7 set in EE0x0c). A bad EEPROM load is detected.

DISCHARGING The bq2040 determines that it is not

being charged.

Battery detects that it is being

charged.

FULLY_CHARGED

The bq2040 determines a valid

charge termination or a maximum

overcharge state.

RM discharges below the full charge

percentage.

FULLY_DISCHARGED

bq2040 determines that it has

supplied all the charge that it can

without being damaged.

RelativeStateOfCharge is greater

than or equal to 20%

Table 9. BatteryStatus Bits

bq2040

Description

EEPROM

Address EEPROM

Hex Contents

Example

Values Notes

Low

Byte High

Byte Low

Byte High

Byte

EEPROM

length 0x00 64 100 Must be equal to 0x64.

EEPROM check 1 0x01 5b 91 Must be equal to 0x5b.

Remaining time

alarm 0x02 0x03 0a 00 10 minutes Sets the low time alarm level.

Remaining

capacity alarm 0x04 0x05 f0 00 240mAh Sets the low capacity alarm level.

Reserved 0x06 0x07 00 00 0 Not currently used by the bq2040.

Initial charging

current 0x08 0x09 60 09 2400mA Sets the initial charge request.

Charging voltage 0x0a 0x0b d8 40 16600mV Used to set the fast-charge voltage for the Smart

Charger.

Battery status 0x0c 0x0d 80 00 128 Initializes BatteryStatus.

Cycle count 0x0e 0x0f 00 00 0 Contains the charge cycle count and can be set to zero

for a new battery.

Design capacity 0x10 0x11 60 09 2400mAh Normal battery pack capacity.

Design voltage 0x12 0x13 40 38 14400mV Nominal battery pack voltage.

Specification

information 0x14 0x15 10 00 1.0 Default value for this register in a 1.0 part.

Manufacture

date 0x16 0x17 a1 20 May 1, 1996

= 8353 Packed per the ManufactureDate description.

Serial number 0x18 0x19 12 27 10002 Contains the optional pack serial number.

Fast-charging

current 0x1a 0x1b 60 09 2400mA Used to set the fast-charge current for the Smart

Charger.

Maintenance

charge current 0x1c 0x1d 00 00 0mA Contains the desired maintenance current after fast-

charge termination by the bq2040.

Reserved 0x1e 0x1f 00 00 0 Must be programmed to 0x00.

Current

overload 0x2c 0x2d 70 17 6000mA Sets the discharge current at which EDV threshold

monitoring is disabled.

Battery low % 0x2e 08 3%

Sets the battery capacity that RemainingCapacity is

reduced to at EDV1. The value equals 2.56 ∗(%RM at

EDV1)

Table 10. Example Register Contents

bq2040

Description

EEPROM

Address

EEPROM

Hex

Contents

Example

Values Notes

Low

Byte High

Byte Low

Byte High

Byte

Reserved 0x2f 00 0 Not currently used by the bq2040.

Li-Ion taper

current 0x38 0x39 10 ff 240mA Sets the upper taper limit for Li-Ion charge termina-

tion. Stored in 2’s complement.

Maximum

overcharge

limit

0x3a 0x3b 9c ff 100mAh

Sets the maximum amount of overcharge before a

maximum overcharge charge suspend occurs.

Stored in 2’s complement.

Reserved 0x3c 00 0 Must be programmed to 0.

Access protect 0x3d b0 SBD access only

If the bq2040 is reset and bit 3 of this location is 0, the

bq2040 locks access to any command outside of the SBS

data set. Program to 0xb8 for full R/W access, 0xb0 for

SBD access only.

FLAGS1 0x3e 00 0 Initializes FLAGS1

FLAGS2 0x3f b0

Relative display

Li-Ion chemistry

bq2040 charge

control

Initializes FLAGS2.

Current

measurement

gain10x46 0x47 00 0f 3840

The current gain measurement and current integra-

tion gain are related and defined for the bq2040 cur-

rent measurement. This word equals 192/sense re-

sistor value in ohms.

Battery voltage

offset10x48 fe -2mV

Used to adjust the battery voltage offset according to

the following:

Voltage = (VSB(mV) + VOFF)∗Voltage gain

Temperature

offset10x49 8a 13.8°C

The default value (zero adjustment) for the offset is

12.8°C or 0x80.

TOFFNEW = TOFFCURRENT +

(TEMPACTUAL - TEMPREPORTED)∗10

Maximum

temperature

and ∆T step

0x4a 5f

Maximum

temperature =

61.0°C

∆T step = 4.6°C

Maximum charge temperature is 69- (mt ∗1.6)°C (mt

= upper nibble). The ∆T step is (dT ∗2 + 16)/10°C

(dT = lower nibble).

Charge

efficiency 0x4b ff

Maintenance

compensation =

100%

Fast compensa-

tion = 100%

Sets the fast-charge (high) and maintenance charge

(low) efficiencies. The upper nibbles sets the low effi-

ciency and the lower nibble adjusts the high effi-

ciency according to the equation:

Nibble = (efficiency% ∗256 - 196)/4

Full-charge

percentage 0x4c 9c 100%

This packed field is the two’s complement of the de-

sired value in RM when the bq2040 determines a

full-charge termination. If RM is below this value,

RM is set to this value. If RM is above this value,

then RM is not adjusted.

Note: 1. Can be adjusted to calibrate the battery pack.

Table 10. Example Register Contents (Continued)

bq2040

Description

EEPROM

Address

EEPROM

Hex

Contents Example

Values Notes

Low

Byte High

Byte Low

Byte High

Byte

Digital filter 0x4d 96 0.30mV Used to set the digital magnitude filter as described in

Table 2.

Current integra-

tion gain10x4e 40 0 3.2/0.05

Represents the following: 3.2/sense resistor in ohms.

It is used by the bq2040 to scale the measured voltage

values on the SR pin in mA and mAh. This register

also compensates for variations in the reported sense

resistor value.

Self-discharge rate 0x4f 2d 0.25%

This packed field is the two’s complement of (52.73/x)

where x is the desired self-discharge rate per day (%)

at room temperature.

Voltage gain10x56 0x57 17 07 7.09

Voltage gain is packed as two units. For example, (R4

+ R5)/R4 = 7.09 would be stored as: whole number

stored in 0x57 as 7 and the decimal component stored

in 0x56 as 256 x 0.09 = 23(= 17h).

Reserved 0x58 0x59 00 00 0 Should be programmed to 0.

EDVF charging

current 0x5a 0x5b 64 00 100mA Contains the desired charge current below EDVF.

End of discharge

voltage 1 0x5c 0x5d 20 d1 12000mV The value programmed is the two’s complement of the

threshold voltage in mV.

End-of-discharge

voltage final 0x5e 0x5f 40 d4 11200mV The value programmed is the two’s complement of the

threshold voltage in mV.

Full charge

capacity 0x60 0x61 d0 07 2000mA This value sets the initial estimated pack capacity.

∆t step 0x62 0f 20s The ∆t step for ∆T/∆t termination equals

320 - (byte value ∗20).

Hold-off time 0x63 00 320s hold-off The hold-off time is 320 - (byte value ∗20).

EEPROM check 2 0x64 b5 181 Must be equal to 0xb5.

Reserved 0x65 0x7f NA Not currently used by the bq2040.

Note: 1. Can be adjusted to calibrate the battery pack.

Table 10. Example Register Contents (Continued)

bq2040

String Description Address 0x

X0 0x

X1 0x

X2 0x

X3 0x

X4 0x

X5 0x

X6 0x

X7 0x

X8 0x

X9 0x

Xa 0x

Manufacturer name 0x20-

0x2b 09 42

Q--

Device name 0x30-

0x37 06 42

Device chemistry 0x40-

0x45 04 6c

N-

Manufacturer data 0x50-

0x55 05 42

Table 11. Example Register Contents (String Data)

bq2040

Absolute Maximum Ratings

Symbol Parameter Minimum Maximum Unit Notes

VCC Relative to VSS -0.3 +7.0 V

All other pins Relative to VSS -0.3 +7.0 V

REF Relative to VSS -0.3 +8.5 V Current limited by R11 (see Figure 1)

VSR Relative to VSS -0.3 +7.0 V

Minimum 100Ωseries resistor should

be used to protect SR in case of a

shorted battery.

TOPR Operating tempera-

ture 0 +70 °C Commercial

Note: Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional opera-

tion should be limited to the Recommended DC Operating Conditions detailed in this data sheet. Expo-

sure to conditions beyond the operational limits for extended periods of time may affect device reliability.

DC Voltage Thresholds (TA=T

OPR; V = 3.0 to 5.5V)

Symbol Parameter Minimum Typical Maximum Unit Notes

EVSB Battery voltage error relative to SB -50mV - 50mV V See note

Note: The accuracy of the voltage measurement may be improved by adjusting the battery voltage offset and

gain, stored in external EEPROM. For best operation, VCC should be 1.5V greater than VSB.

bq2040

Recommended DC Operating Conditions (TA= TOPR)

Symbol Parameter Minimum Typical Maximum Unit Notes

VCC Supply voltage 3.0 4.25 6.5 V VCC excursion from < 2.0V to ≥

3.0V initializes the unit.

VREF

Reference at 25°C 5.7 6.0 6.3 V IREF = 5µA

Reference at -40°C to +85°C 4.5 - 7.5 V IREF = 5µA

RREF Reference input impedance 2.0 5.0 - MΩVREF = 3V

ICC Normal operation

- 90 135 µAV

CC = 3.0V

- 120 180 µAV

CC = 4.25V

- 170 250 µAV

CC = 5.5V

VSB Battery input 0 - VCC V

RSBmax SB input impedance 10 - - MΩ0 < VSB < VCC

IDISP DISP input leakage - - 5 µAV

DISP = VSS

ILVOUT VOUT output leakage -0.2 - 0.2 µA EEPROM off

VSR Sense resistor input -0.3 - 2.0 V VSR <V

SS = discharge;

VSR > VSS = charge

RSR SR input impedance 10 - - MΩ-200mV < VSR < VCC

VIH Logic input high 0.5 ∗VCC -VCC V ESCL, ESDA

1.4 - 5.5 V SMBC, SMBD

VIL Logic input low 0-

0.3 ∗VCC V ESCL, ESDA

-0.5 0.6 V SMBC, SMBD

VOL Data, clock output low - - 0.4 V IOL=350µA, SMBC, SMBD

IOL Sink current 100 - 350 µAV

OL≤0.4V, SMBC, SMBD

VOLSL LEDXoutput low, low VCC - 0.1 - V VCC = 3V, IOLS ≤1.75mA

LED1–LED4

VOLSH LEDXoutput low, high VCC - 0.4 - V VCC = 6.5V, IOLS ≤11.0mA

LED1–LED4

VOHVL VOUT output, low VCC VCC - 0.3 - - V VCC = 3V, IVOUT = -5.25mA

VOHVH VOUT output, high VCC VCC - 0.6 - - V VCC = 6.5V, IVOUT = -33.0mA

IVOUT VOUT source current -33 - - mA At VOHVH = VCC - 0.6V

IOLS LEDXsink current 11.0 - mA At VOLSH = 0.4V

Note: All voltages relative to VSS.

bq2040

Symbol Parameter Min Max Units Notes

FSMB SMBus operating frequency 10 100 KHz

TBUF Bus free time between stop and

start condition 4.7 µs

THD:STA Hold time after (repeated) start

condition 4.0 µs

TSU:STA Repeated start condition setup time 4.7 µs

TSU:STO Stop condition setup time 4.0 µs

THD:DAT Data hold time 300 ns

TSU:DAT Data setup time 250 ns

TLOW Clock low period 4.7 µs

THIGH Clock high period 4.0 µs

TFClock/data fall time 300 ns

TRClock/data rise time 1000 ns

TLOW:SEXT Cumulative clock low extend time

(slave) 25 ms

TTIMEOUT 25 35 ms

AC Specifications

TD294501.eps

SU:STA

SMBC

SMBD

SU:STO

BUF

HD:STA

LOW

SU:DAT

HIGH

HD:DAT

Bus Timing Data

bq2040

16-Pin SOIC Narrow (SN)

16-Pin SN (SOIC Narrow)

Dimension Minimum Maximum

A 0.060 0.070

A1 0.004 0.010

B 0.013 0.020

C 0.007 0.010

D 0.385 0.400

E 0.150 0.160

e 0.045 0.055

H 0.225 0.245

L 0.015 0.035

All dimensions are in inches.

.004

bq2040

Ordering Information bq2040

Package Option:

SN = 16-pin narrow SOIC

Device:

bq2040 Gas Gauge IC With SMBus Interface

Temperature Range:

blank = Commercial (0 to 70°C)

ChangeNo. Page No. Description of Change

3 3 Updated recommended application schematic.

3 9 Changed overcurrent fault conditon for ChargingCurrent < 1024mA.

3 10 4Hz operation of LED clarification.

3 11 Added descriptions for bits 7 and 13 of BatteryMode.

3 14 AtRateTimeToEmpty and AtRateTimeToFull invalid data indication correction.

3 15, 16 RunTimeToEmpty, AverageTimeToEmpty and AverageTimeToFull invalid data

indication corrections.

3 23 Changed typical Battery low % value for Li-Ion with EDV1 = 3.0V/cell.

3 24 Li-Ion taper current is stored in 2’s complement.

324

Changed typical ∆T step and Full-charge percentage for Li-Ion.

3 25 Voltage gain is (R4 + R5)/R4.

3 25 Changed typical EDV1 and EDVF values for Li-Ion.

4 6 Added VSB should not exceed 2.4V

4 8 The self discharge rate approx imately doubles or halves

4 11 Changed cycle count increase from 30 to 32 for condition request.

4 14 Changed AtRateOK() indication from EDV1 to EDVF

4 25 Changed self-discharge programming from 52.75/x to 52.73/x.

4 25 Changed recommended EDVF charging current from 0mA to 100mA

Notes: Changes 1 and 2 refer to the 1998 Data Book

Change 3 = June1998 D changes from Jan. 1998 C.

Change 4 = June 1999 E changes from June 1998 D.

Data Sheet Revision History

PACKAGING INFORMATION

Orderable Device Status (1) Package

Type Package

Drawing Pins Package

Qty Eco Plan (2) Lead/Ball Finish MSL Peak Temp (3)

BQ2040SN-C408 ACTIVE SOIC D 16 40 Green (RoHS &