LP4951CMX/NOPB - NATIONAL SEMICONDUCTOR

LP4950C-5V,LP4951C

LP4950C-5V and LP4951C Adjustable Micropower Voltage Regulators

Literature Number: SNVS208A

LP4950C-5V and LP4951C

Adjustable Micropower Voltage Regulators

General Description

The LP4950C and LP4951C are micropower voltage regu-

lators with very low quiescent current (75µA typ.) and very

low dropout voltage (typ. 40mV at light loads and 380mV at

100mA). They are ideally suited for use in battery-powered

systems. Furthermore, the quiescent current of the

LP4950C/LP4951C increases only slightly in dropout, pro-

longing battery life.

The LP4950C in the popular 3-pin TO-92 package is pin

compatible with older 5V regulators. The 8-lead LP4951C is

available in a plastic surface mount package and offers

additional system functions.

One such feature is an error flag output which warns of a low

output voltage, often due to falling batteries on the input. It

may be used for a power-on reset. A second feature is the

logic-compatible shutdown input which enables the regulator

to be switched on and off. Also, the part may be pin-strapped

for a 5V output or programmed from 1.24V to 29V with an

external pair of resistors.

Careful design of the LP4950C/LP4951C has minimized all

contributions to the error budget. This includes a tight initial

tolerance (.5% typ.), extremely good load and line regulation

(.05% typ.) and a very low output voltage temperature coef-

ficient, making the part useful as a low-power voltage refer-

ence.

Features

nHigh accuracy 5V guaranteed 100mA output

nExtremely low quiescent current

nLow dropout voltage

nExtremely tight load and line regulation

nVery low temperature coefficient

nUse as Regulator or Reference

nNeeds only 1µF for stability

nCurrent and Thermal Limiting

LP4951C versions only

nError flag warns of output dropout

nLogic-controlled electronic shutdown

nOutput programmable from 1.24 to 29V

Block Diagram and Typical Applications

LP4950C LP4951C

20052825

20052801

August 2005

LP4950C-5V and LP4951C Adjustable Micropower Voltage Regulators

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Input Supply Voltage −0.3 to +30V

SHUTDOWN Input Voltage,

Error Comparator Output

Voltage, (Note 9)

−0.3 to +30V

FEEDBACK Input Voltage −1.5 to +30V

(Note 9) (Note 10)

Power Dissipation Internally Limited

Junction Temperature (T

) +150˚C

Ambient Storage Temperature −65˚ to +150˚C

Soldering Dwell Time, Temperature

Wave

Infrared

Vapor Phase

4 seconds, 260˚C

10 seconds, 240˚C

75 seconds, 219˚C

ESD TBD

Operating Ratings (Note 1)

Maximum Input Supply Voltage 30V

Junction Temperature Range

(Note 8)

LP4950C, LP4951C −40˚C to 125˚C

Electrical Characteristics (Note 2)

Parameter Conditions

(Note 2)

LP4950CZ

Units

LP4951CM

Tested Design

Typ Limit Limit

(Note 3) (Note 4)

Output Voltage T

= 25˚C 5.0 5.1 V max

4.9 V min

−25˚C ≤T

≤85˚C 5.15 V max

4.85 V min

Full Operating 5.2 V max

Temperature Range 4.8 V min

Output Voltage 100 µA ≤I

≤100 mA 5.24 V max

≤T

JMAX

4.76 V min

Output Voltage

Temperature Coefficient

(Note 12) 150 ppm/˚C

Line Regulation

(Note 14)

6V ≤V

≤30V (Note 15) 0.04 0.2 % max

0.4 % max

Load Regulation

(Note 14)

100µA ≤I

≤100mA 0.1 0.2 % max

0.3 % max

Dropout Voltage

(Note 5)

= 100µA 50 80 mV max

150 mV max

= 100mA 380 450 mV max

600 mV max

Ground Current I

= 100µA 75 150 µA max

170 µA max

= 100mA 8 15 mA max

19 mA max

Dropout Ground Current V

= 4.5V 110 200 µA max

= 100µA 230 µA max

Current Limit V

OUT

= 0 160 200 mA max

220 mA max

Thermal Regulation (Note 13) 0.05 0.2 %/W max

Output Noise, C

= 1µF 430 µV rms

10 Hz to 100 kHz C

= 200µF 160 µV rms

= 3.3µF (Bypass = 0.01µF

Pins 7 to 1 (LP4951C)

100 µV rms

LP4950C-5V and LP4951C

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Electrical Characteristics

LP4951C

Parameter Conditions (Note 2) Typ Tested

Limit (Note

Desgin

Limit (Note

Units

8-PIN VERSIONS ONLY

Reference Voltage 1.235 1.285 V max

1.295 V max

1.185 V min

1.165 Vmin

Reference Voltage (Note 7) 1.335 V max

1.135 V min

Feedback Pin Bias

Current

20 40 nA max

60 nA max

Reference Voltage

Temperature Coefficient

(Note 12) 50 ppm/˚C

Feedback Pin Bias

Current Temperature

Coefficient

0.1 nA/˚C

Error Comparator

Output Leakage Current VOH = 30V 0.01 1 µA max

2µA max

Output Low Voltage V

= 4.5V

= 400µA

150 250 mV max

400 mV max

Upper Threshold Voltage (Note 4) 60 40 mV min

25 mV min

Lower Threshold Voltage (Note 6) 75 95 mV max

140 mV max

Hysteresis (Note 6) 15 mV

Shutdown Input

Input Logic Voltage 1.3 V

Low (Regulator ON) 0.7 V max

High (Regulator OFF) 2.0 V min

Shutdown Pin Input

Current

SHUTDOWN

= 2.4V 30 50 µA max

100 µA max

SHUTDOWN

= 30V 450 600 µA max

750 µA max

Regulator Output Current

in Shutdown

(Note 11) 3 10 µA max

20 µA max

Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device

is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical

Characteristics tables.

Note 2: Unless otherwise specified all limits guaranteed for VIN =6V,I

L= 100µA and CL= 1µF. Limits appearing in boldface type apply over the entire junction

temperature range for operation. Limits appearing in normal type apply for TA=T

J= 25˚C. Additional conditions for the 8-pin versions are FEEDBACK tied to VTAP,

OUTPUT tied to SENSE (VOUT = 5V), and VSHUTDOWN ≤0.8V.

Note 3: Guaranteed and 100% production tested.

Note 4: Guaranteed but not 100% production tested. These limits are not used to calculate outgoing AQL levels.

Note 5: Dropout Voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value measured at 1V differential.

At very low values of programmed output voltage, the minimum input supply voltage of 2V (2.3V over temperature) must be taken into account.

Note 6: Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured at VIN =

6V. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = VOUT/VREF = (R1 + R2)/R2.For example, at a programmed

output voltage of 5V, the Error output is guaranteed to go low when the output drops by 95 mV x 5V/1.235V = 384 mV.Thresholds remain constant as a percent of

VOUT as VOUT is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.

Note 7: VREF ≤VOUT ≤(VIN − 1V), 2.3V ≤VIN ≤30V, 100µA ≤IL≤100mA, TJ≤TJMAX.

Note 8: The junction-to-ambient thermal resistances are as follows: 180˚C/W and 160˚C/W for the TO-92 package with 0.40 inch and 0.25 inch leads to the printed

circuit board (PCB) respectively, 160˚C/W for the molded plastic SOP (M). The above thermal resistances for the M package apply when the package is soldered

directly to the PCB.

LP4950C-5V and LP4951C

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Electrical Characteristics (Continued)

Note 9: May exceed input supply voltage.

Note 10: When used in dual-supply systems where the output terminal sees loads returned to a negative supply, the output voltage should be diode-clamped to

ground.

Note 11: VSHUTDOWN ≥2V, VIN ≤30V, VOUT = 0, Feedback pin tied to VTAP.

Note 12: Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.

Note 13: Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load or line regulation

effects. Specifications are for a 50 mA load pulse at VIN = 30V (1.25W pulse) for T = 10ms.

Note 14: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are

covered under the specification for thermal regulation.

Note 15: Line regulation for the LP4951C is tested at 150˚C for IL= 1 mA. For IL= 100µA and TJ= 125˚C, line regulation is guaranteed by design to 0.2%. See

Typical Performance Characteristics for line regulation versus temperature and load current.

Connection Diagrams

TO-92 Plastic Package (Z) Surface-Mount Package (M)

20052802

Bottom View

20052826

Top View

Ordering Information

Package Output Voltage Temperature

5.0V

TO-92 (Z) LP4950CZ-5.0 −40˚C <T

<125˚C

M (M08A) LP4951CM −40˚C <T

<125˚C

LP4950C-5V and LP4951C

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Typical Performance Characteristics

Quiescent Current Dropout Characteristics

20052827 20052828

Input Current Input Current

20052829 20052830

Output Voltage vs. Temperature of 3

Representative Units Quiescent Current

20052831 20052832

LP4950C-5V and LP4951C

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Typical Performance Characteristics (Continued)

Quiescent Current Quiescent Current

20052833 20052834

Quiescent Current Short Circuit Current

20052835 20052836

Dropout Voltage Dropout Voltage

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20052838

LP4950C-5V and LP4951C

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Typical Performance Characteristics (Continued)

LP4951C Minimum Operating Voltage LP4951C Feedback Bias Current

20052839 20052840

LP4951C Feedback Pin Current LP4951C Error Comparator Output

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20052842

LP4951C Comparator Sink Current Line Transient Response

20052843 20052844

LP4950C-5V and LP4951C

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Typical Performance Characteristics (Continued)

Load Transient Response Load Transient Response

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LP4951C Enable Transient Output Impedance

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20052848

Ripple Rejection Ripple Rejection

20052849 20052850

LP4950C-5V and LP4951C

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Typical Performance Characteristics (Continued)

Ripple Rejection Output Noise

20052851 20052852

LP4951C Divider Resistance Shutdown Threshold Voltage

20052853 20052854

Line Regulation LP4951C Maximum Rated Output Current

20052855 20052857

LP4950C-5V and LP4951C

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Typical Performance Characteristics (Continued)

Thermal Response

20052858

Application Hints

EXTERNAL CAPACITORS

A 1.0µF (or greater) capacitor is required between the output

and ground for stability at output voltages of 5V or more. At

lower output voltages, more capacitance is required. Without

this capacitor the part will oscillate. Most types of tantalum or

aluminum electrolytics work fine here; even film types work

but are not recommended for reasons of cost. Many alumi-

num electrolytics have electrolytes that freeze at about

−30˚C, so solid tantalums are recommended for operation

below −25˚C. The important parameters of the capacitor are

an ESR of about 5 Ωor less and a resonant frequency above

500 kHz. The value of this capacitor may be increased

without limit.

At lower values of output current, less output capacitance is

required for stability. The capacitor can be reduced to

0.33 µF for currents below 10 mA or 0.1 µF for currents

below 1 mA. Using the 8-pin version at voltages below 5V

runs the error amplifier at lower gains so that more output

capacitance is needed. For the worst-case situation of a

100 mA load at 1.23V output (Output shorted to Feedback) a

3.3 µF (or greater) capacitor should be used.

Unlike many other regulators, the LP4950C will remain

stable and in regulation with no load in addition to the

internal voltage divider. This is especially important in CMOS

RAM keep-alive applications. When setting the output volt-

age of the LP4951C version with external resistors, a mini-

mum load of 1µA is recommended.

A 0.1µF capacitor should be placed from the LP4950C/

LP4951C input to ground if there is more than 10 inches of

wire between the input and the AC filter capacitor or if a

battery is used as the input.

Stray capacitance to the LP4951C Feedback terminal (pin 7)

can cause instability. This may especially be a problem when

using high value external resistors to set the output voltage.

Adding a 100pF capacitor between Output and Feedback

and increasing the output capacitor to at least 3.3µF will fix

this problem.

ERROR DETECTION COMPARATOR OUTPUT

The comparator produces a logic low output whenever the

LP4951C output falls out of regulation by more than approxi-

mately 5%. This figure is the comparator’s built-in offset of

about 60 mV divided by the 1.235 reference voltage. (Refer

to the block diagram in the front of the datasheet.) This trip

level remains “5% below normal” regardless of the pro-

grammed output voltage of the 4951C. For example, the

error flag trip level is typically 4.75V for a 5V output or 11.4V

for a 12V output. The out of regulation condition may be due

either to low input voltage, current limiting, or thermal limit-

ing.

Figure 1 below gives a timing diagram depicting the ERROR

signal and the regulated output voltage as the LP4951C

input is ramped up and down. The ERROR signal becomes

valid (low) at about 1.3V input. It goes high at about 5V input

(the input voltage at which V

OUT

= 4.75V). Since the

LP4951C’s dropout voltage is load-dependent (see curve in

typical performance characteristics), the input voltage trip

point (about 5V) will vary with the load current. The output

voltage trip point (approx. 4.75V) does not vary with load.

The error comparator has an open-collector output which

requires an external pullup resistor. This resistor may be

returned to the output or some other supply voltage depend-

ing on system requirements. In determining a value for this

resistor, note that while the output is rated to sink 400µA, this

sink current adds to battery drain in a low battery condition.

Suggested values range from 100k to 1 MΩ. The resistor is

not required if this output is unused.

LP4950C-5V and LP4951C

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Application Hints (Continued)

PROGRAMMING THE OUTPUT VOLTAGE (LP4951C)

The LP4951C may be pin-strapped for 5V using its internal

voltage divider by tying the pin 1 (output) to pin 2 (sense)

pins together, and also tying the pin 7 (feedback) and pin 6

TAP

) pins together. Alternatively, it may be programmed for

any output voltage between its 1.235V reference and its 30V

maximum rating. As seen in Figure 2, an external pair of

resistors is required.

The complete equation for the output voltage is

where V

REF

is the nominal 1.235 reference voltage and I

the feedback pin bias current, nominally −20 nA. The mini-

mum recommended load current of 1µA forces an upper limit

of 1.2 MΩon the value of R

, if the regulator must work with

no load (a condition often found in CMOS in standby). I

will

produce a 2% typical error in V

OUT

which may be eliminated

at room temperature by trimming R

. For better accuracy,

choosing R

= 100k reduces this error to 0.17% while in-

creasing the resistor program current to 12µA. Since the

LP4951C typically draws 60µA at no load with Pin 2 open-

circuited, this is a small price to pay.

REDUCING OUTPUT NOISE

In reference applications it may be advantageous to reduce

the AC noise present at the output. One method is to reduce

the regulator bandwidth by increasing the size of the output

capacitor. This is the only way noise can be reduced on the

3 lead LP4950C but is relatively inefficient, as increasing the

capacitor from 1µF to 220µF only decreases the noise from

430µV to 160µV rms for a 100kHz bandwidth at 5V output.

Noise can be reduced fourfold by a bypass capacitor across

, since it reduces the high frequency gain from 4 to unity.

Pick

or about 0.01µF. When doing this, the output capacitor must

be increased to 3.3µF to maintain stability. These changes

reduce the output noise from 430µV to 100µV rms for a

100kHz bandwidth at 5V output. With the bypass capacitor

added, noise no longer scales with output voltage so that

improvements are more dramatic at higher output voltages.

20052820

*When VIN ≤1.3V, the error flag pin becomes a high impedance, and the

error flag voltage rises to its pull-up voltage. Using VOUT as the pull-up

voltage (see Figure 2), rather than an external 5V source, will keep the

error flag voltage under 1.2V (typ.) in this condition. The user may wish to

divide down the error flag voltage using equal-value resistors (10 kΩ

suggested), to ensure a low-level logic signal during any fault condition,

while still allowing a valid high logic level during normal operation.

FIGURE 1. ERROR Output Timing

20052807

*See Application Hints

**Drive with TTL-high to shut down. Ground or leave open if shutdown

feature is not to be used.

Note: Pins 2 and 6 are left open.

FIGURE 2. Adjustable Regulator (LP4951C)

LP4950C-5V and LP4951C

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Schematic Diagram

20052823

LP4950C-5V and LP4951C

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Physical Dimensions inches (millimeters) unless otherwise noted

Surface Mount Package (M)

NS Package Number M08A

Molded TO-92 Package (Z)

NS Package Number Z03A

LP4950C-5V and LP4951C

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Notes

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves

the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

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2. A critical component is any component of a life support

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LP4950C-5V and LP4951C Adjustable Micropower Voltage Regulators

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