General Description
The MAX6979 serial-interfaced LED driver provides 16
open-drain, constant-current-sinking LED driver outputs
rated at 5.5V. The MAX6979 operates from a 3V to 5.5V
supply. The MAX6979 supply and the LEDs’ supply can
power up in any order. The constant-current outputs
are programmed together to up to 55mA using a single
external resistor. The MAX6979 operates with a 25Mb,
industry-standard, 4-wire serial interface.
The MAX6979 includes circuitry that automatically
detects open-circuit LEDs. Fault status is loaded into the
serial-interface shift register when LE goes high and is
automatically shifted out on DOUT when the next data
transmission is shifted in.
The MAX6979 includes a fail-safe feature for safety-
related applications, which blanks the display if the ser-
ial interface fails. If the serial interface becomes
inactive for more than 1s, all driver output latches are
automatically cleared. This turns off all LEDs connected
to the outputs. The shift register data is not disturbed.
The outputs remain off until the driver output latches are
updated with data turning them on, so recovery is auto-
matic if the transmission failure is temporary. The
watchdog function requires no software change to the
application driving the MAX6979.
The MAX6979 uses the industry-standard shift-register-
plus-latch-type serial interface. The driver accepts data
shifted into a 16-bit shift register using data input DIN
and clock input CLK. Input data appears at the output
DOUT 16 clock cycles later to allow cascading of multi-
ple MAX6979s. The latch-enable input, LE, loads the 16
bits of shift-register data into a 16-bit output latch to set
which LEDs are on and which are off. The output-
enable input, OE, gates all 16 outputs on and off, and is
fast enough to be used as a PWM input for LED intensi-
ty control.
The MAX6979 is one of a family of 12 shift-register-plus-
latch-type LED drivers. The family includes 8-port and
16-port types, with 5.5V- or 36V-rated LED outputs, with
and without open-circuit LED detection and watchdog.
All versions operate from a 3V to 5.5V supply, and are
specified over the -40°C to +125°C temperature range.
Features
o25Mb Industry-Standard, 4-Wire Serial Interface at 5V
o3V to 5.5V Logic Supply
o16 Constant-Current LED Outputs Rated at 5.5V
oUp to 55mA Continuous Current per Output
oOutput Current Programmed by Single Resistor
o3% Current Matching Between Outputs
o6% Current Matching Between ICs
oWatchdog Clears Display if Interface Fails
oReports Open-Circuit LED Faults
oHigh-Dissipation, 24-Pin Packages
o-40°C to +125°C Temperature Range
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
________________________________________________________________
Maxim Integrated Products
1
24
23
22
21
20
19
18
17
1+
2
3
4
5
6
7
8
V+
SET
DOUT
OELE
CLK
DIN
GND
TOP VIEW
OUT15
OUT14
OUT13
OUT12OUT3
OUT2
OUT1
OUT0
16
15
14
13
9
10
11
12
OUT11
OUT10
OUT9
OUT8OUT7
OUT6
OUT5
OUT4
TSSOP/PDIP
MAX6979AUG
MAX6979APG
Pin Configuration
Ordering Information
19-3703; Rev 1; 12/10
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Typical Application Circuit and Selector Guide appear at
end of data sheet.
Applications
Variable Message Signs
Marquee Displays
Point-of-Order Signs
Traffic Signs
Gaming Features
Architectural Lighting
PART TEMP RANGE PIN-PACKAGE
MAX6979AUG+ -40°C to +125°C 24 TSSOP
MAX6979APG+ -40°C to +125°C 24 PDIP
+
Denotes a lead(Pb)-free/RoHS-compliant package.
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage (with respect to GND)
V+ .............................................................................-0.3V to +6V
OUT_ ........................................................................-0.3V to +6V
DIN, CLK, LE, OE, SE ..................................-0.3V to (V+ + 0.3V)
DOUT_ Current .................................................................±10mA
OUT_ Sink Current ..............................................................60mA
Total GND Current ............................................................960mA
Continuous Power Dissipation (TA= +70°C)
24-Pin PDIP (derate 13.3mW/°C over +70°C)............1067mW
24-Pin TSSOP (derate 12.2mW/°C over +70°C) .........975mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow)
Lead(Pb)-free packages..............................................+260°C
Packages containing lead(Pb).....................................+240°C
ELECTRICAL CHARACTERISTICS
(
Typical Operating Circuit
, V+ = 3V to 5.5V, TA= TMIN to TMAX, unless otherwise noted. Typical values are at V+ = 5V, TA= +25°C.)
(Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Operating Supply Voltage V+ 3.0 5.5 V
Output Voltage VOUT 5.5 V
Standby Current
(Interface Idle, All Output Ports
High Impedance, RSET = 360Ω)
I+All logic inputs at V+ or GND, DOUT
unloaded 5.7 8 mA
Standby Current
(Interface Running, All Output
Ports High Impedance,
RSET = 360Ω)
I+fCLK = 5MHz, OE = V+, DIN and LE = V+
or GND, DOUT unloaded 6 8.5 mA
Supply Current
(Interface Idle, All Output Ports
Active Low, RSET = 360Ω)
I+All logic inputs at V+ or GND,
DOUT unloaded 18 25 mA
Input High Voltage
DIN, CLK, LE, OE VIH 0.7 x
V+ V
Input Low Voltage
DIN, CLK, LE, OE VIL 0.3 x
V+ V
Hysteresis Voltage
DIN, CLK, LE, OE ∆VI0.8 V
Input Leakage Current
DIN, CLK, LE, OE IIH, IIL -1 +1 µA
Output High Voltage DOUT VOH ISOURCE = 4mA V +
- 0.5V V
Output Low Voltage VOL ISINK = 4mA 0.5 V
Output Current OUT IOUT V+ = 3V to 5.5V, VOUT = 0.5V to 2.5V,
RSET = 360Ω37 50 61 mA
Output Leakage Current OUT ILEAK OE = V+, VOUT = V+ 1 µA
Watchdog Timeout tWD 0.1 1 2.5 s
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
_______________________________________________________________________________________ 3
5V TIMING CHARACTERISTICS
(
Typical Operating Circuit
, V+ = 4.5V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Notes 1 and 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CLK Clock Period tCP 40 ns
CLK Pulse-Width High tCH 19 ns
CLK Pulse-Width Low tCL 19 ns
DIN Setup Time tDS 4ns
DIN Hold Time tDH 8ns
DOUT Propagation Delay tDO 12 32 ns
DOUT Rise and Fall Time tDR, tDF CDOUT = 10pF, 20% to 80% 10 ns
LE Setup Time tLS 10 ns
LE Rising to OUT Rising Delay tLRR (Note 2) 100 ns
LE Rising to OUT Falling Delay tLRF (Note 2) 300 ns
C LK Ri si ng to O U T Ri si ng D el ay tCRR (Note 2) 100 ns
C LK Ri si ng to O U T Fal l i ng D el ay tCRF (Note 2) 310 ns
OE Rising to OUT Rising Delay tOEH100 ns
OE Falling to OUT Falling Delay tOEL320 ns
LED Output OUT Turn-On Fall
Time tf80% to 20%; pullup resistor = 65Ω120 ns
LED Output OUT Turn-Off Rise
Time tr20% to 80%; pullup resistor = 65Ω120 ns
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
4 _______________________________________________________________________________________
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS OFF,
RSET = 720Ω)
MAX6979 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
5.04.53.5 4.0
2.75
3.00
3.25
3.50
3.75
4.00
4.25
4.50
2.50
3.0 5.5
TA = +125°CTA = +85°C
TA = -40°CTA = +25°C
4.0
4.6
4.4
4.2
4.8
5.0
5.2
5.4
5.6
5.8
6.0
3.0 4.03.5 4.5 5.0 5.5
MAX6979 toc02
SUPPLY VOLTAGE
(
V
)
SUPPLY CURRENT (mA)
TA = +125°CTA = +85°C
TA = -40°C
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS OFF,
RSET = 360Ω)
TA = +25°C
6
8
16
14
12
10
18
20
3.0 4.03.5 4.5 5.0 5.5
MAX6979 toc03
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS ON,
RSET = 720Ω)
TA = +125°CTA = +85°C
TA = +25°C
TA = -40°C
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
3.3V TIMING CHARACTERISTICS
(
Typical Operating Circuit
, V+ = 3V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Notes 1 and 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CLK Clock Period tCP 52 ns
CLK Pulse-Width High tCH 24 ns
CLK Pulse-Width Low tCL 24 ns
DIN Setup Time tDS 4ns
DIN Hold Time tDH 8ns
DOUT Propagation Delay tDO 12 50 ns
DOUT Rise and Fall Time CDOUT = 10pF, 20% to 80% 12 ns
LE Setup Time tLS 15 ns
LE Rising to OUT Rising Delay 120 ns
LE Rising to OUT Falling Delay 310 ns
C LK Ri si ng to O U T Ri si ng D el ay 120 ns
C LK Ri si ng to O U T Fal l i ng D el ay 330 ns
OE Rising to OUT Rising Delay tOEH120 ns
OE Falling to OUT Falling Delay tOEL330 ns
LED Output OUT Turn-On Fall
Time tf80% to 20% 120 ns
LED Output OUT Turn-Off Rise
Time tr20% to 80% 120 ns
Note 1: All parameters tested at TA= +25°C. Specifications overtemperature are guaranteed by design.
Note 2: See Figure 3.
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
_______________________________________________________________________________________
5
10
12
16
14
22
20
18
3.0 4.03.5 4.5 5.0 5.5
MAX6979 toc04
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(INTERFACE IDLE, ALL OUTPUTS ON, RSET = 360Ω)
TA = +125°CTA = +85°C
TA = +25°C
TA = -40°C
0
10
5
20
15
25
30
0 1.0 1.50.5 2.0 2.5 3.0
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (RSET = 720Ω, V+ = 3.3V)
MAX6979 toc05
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
0
20
10
40
30
50
60
0 1.0 1.50.5 2.0 2.5 3.0
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (RSET = 360Ω, V+ = 3.3V)
MAX6979 toc06
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = -40°C
TA = +25°C
0
10
5
20
15
25
30
0 1.0 1.50.5 2.0 2.5 3.0
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (RSET = 720Ω, V+ = 5.0V)
MAX6979 toc07
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
0
20
10
40
30
50
60
0 1.0 1.50.5 2.0 2.5 3.0
PORT OUTPUT CURRENT vs. PORT OUTPUT
VOLTAGE (RSET = 360Ω, V+ = 5.0V)
MAX6979 toc08
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
27.0
26.5
26.0
25.5
25.0
24.5
24.0
3.0 4.0
3.5 4.5 5.0 5.5
PORT OUTPUT CURRENT vs. SUPPLY
VOLTAGE (RSET = 720Ω, VOUT = 2V)
MAX6979 toc09
SUPPLY VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
54
53
52
51
50
49
3.0 4.0
3.5 4.5 5.0 5.5
PORT OUTPUT CURRENT vs. SUPPLY
VOLTAGE (RSET = 360Ω, VOUT = 2V)
MAX6979 toc10
SUPPLY VOLTAGE (V)
PORT OUTPUT CURRENT (mA)
TA = +125°C
TA = +85°C
TA = +25°C
TA = -40°C
0
10
30
20
40
50
0600300 900 1200 1500
PORT OUTPUT CURRENT
vs. RSET RESISTANCE (V+ = 5.0V)
MAX6979 toc11
RSET RESISTANCE (Ω)
PORT OUTPUT CURRENT (mA)
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
Detailed Description
The MAX6979 LED driver comprises a 4-wire serial
interface driving eight constant-current sinking open-
drain output ports. The outputs drive LEDs in either sta-
tic or multiplex applications (Figure 1). The constant-
current outputs are guaranteed for current accuracy
not only with chip-supply voltage variations (5V ±10%
and 3V to 5.5V), but also over a realistic range of driver
output voltage drop (0.5V to 2.5V). The drivers use cur-
rent-sensing feedback circuitry (not simple current mir-
rors) to ensure very small current variations over the full
allowed range of output voltage (see the
Typical
Operating Characteristics
).
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
6 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 GND Ground
2 DIN Serial-Data Input. Data is loaded into the internal 16-bit shift register on CLK’s rising edge.
3 CLK Serial-Clock Input. Data is loaded into the internal 16-bit shift register on CLK’s rising edge.
4LE
Load-Enable Input. Data is loaded transparently from the internal shift register(s) to the output latch(es)
while LE is high. Data is latched into the output latch(es) on LE's falling edge, and retained while LE is low.
5–20 OUT0–
OUT15 LED Driver Outputs. OUT0 to OUT15 are open-drain, constant-current-sinking outputs rated to 5.5V.
21 OE Output Enable Input. High forces outputs OUT0 to OUT15 high impedance without altering the contents of
the output latches. Low enables outputs OUT0 to OUT15 to follow the state of the output latches.
22 DOUT Serial-Data Output. Data is clocked out of the 16-bit internal shift register to DOUT on CLK’s rising edge.
23 SET LED Current Setting. Connect SET to GND through a resistor (RSET) to set the maximum LED current.
24 V+ Positive Supply Voltage. Bypass V+ to GND with a 0.1µF ceramic capacitor.
SERIAL-TO-PARALLEL SHIFT REGISTER
LATCHES
OUT0
OUT1
OUT2
DOUT
DIN
CLK
OUT15
CONSTANT-CURRENT SINKS
OUT13
OUT14
POWER-ON
RESET
V+
CURRENT
REFERENCE
V+
OE
GND
GND
LE
D0 D15
D0 D15
D0 D15
RSET
MAX6979
FAULT DETECTION
WATCH-
DOG
Figure 1. MAX6979 Block Diagram
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
_______________________________________________________________________________________ 7
The 4-wire serial interface comprises a 16-bit shift reg-
ister and a 16-bit transparent latch. The shift register is
written through a clock input CLK and a data input DIN
and the data propagates to a data output DOUT. The
data output allows multiple drivers to be cascaded and
operated together. The contents of the 16-bit shift reg-
ister are loaded into the transparent latch through a
latch-enable input LE. The latch is transparent to the
shift register outputs when high, and latches the cur-
rent state on the falling edge of LE.
Each driver output is an open-drain, constant-current
sink that should be connected to the cathode of either
a single LED or a series string of multiple LEDs. The
LED anode can be connected to a supply voltage of up
to 5.5V, independent of the MAX6979 supply, V+. The
constant-current capability is up to 55mA per output,
set for all 16 outputs by an external resistor, RSET.
4-Wire Serial Interface
The serial interface on the MAX6979 is a 4-wire serial
interface using four inputs (DIN, CLK, LE, OE) and a
data output (DOUT). This interface is used to write dis-
play data to the MAX6979. The serial-interface data
word length is 16 bits, D0–D15. See Figure 2.
The functions of the five interface pins are as follows.
DIN is the serial-data input, and must be stable when it
is sampled on the rising edge of CLK. Data is shifted
in, MSB first. This means that data bit D15 is clocked in
first, followed by 15 more data bits, finishing with the
LSB D0.
CLK is the serial-clock input, which shifts data at DIN
into the MAX6979 16-bit shift register on its rising edge.
LE is the latch load input of the MAX6979, which trans-
fers data from the MAX6979 16-bit shift register to its 16-
bit latch when LE is high (transparent latch), and latches
the data on the falling edge of LE (Figure 2).
The fourth input provides output-enable control of the
output drivers. OE is high to force outputs
OUT0–OUT15 high impedance, without altering the
contents of the output latches, and low to enable out-
puts OUT0–OUT15 to follow the state of the output
latches.
OE is independent of the operation of the serial inter-
face. Data can be shifted into the serial-interface shift
register and latched regardless of the state of OE.
DOUT is the serial-data output, which shifts data out
from the MAX6979’s 16-bit shift register on the rising
edge of CLK. Data at DIN is propagated through the
shift register and appears at DOUT 16 clock cycles later.
See Figure 2.
Figure 2. 4-Wire Serial-Interface Timing Diagram
.
D15 D14
tDS
tDH
tCL
tCP
tDO
tOEW
tOEL
tftr
tOEH
tLS
tLW
tCH
D1 D0
D15
LE
CLK
DIN
DOUT
OE
OUT_
80%
20%
tLF
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
8 _______________________________________________________________________________________
Watchdog
The MAX6979 includes a watchdog circuit that monitors
the CLK, DIN, and LE inputs. If there is no transition on
all of these inputs for nominally 1s, then the output latch-
es are cleared and outputs OUT0–OUT15 go high
impedance like the initial power-up condition. This turns
off all LEDs connected to the outputs. The shift-register
data does not change, just the output-latch data.
The watchdog is intended to be used as a fail-safe fea-
ture for applications, which prefer a blank display to an
incorrect display if the serial interface fails. When the
watchdog triggers, the outputs remain off until the dri-
ver output latches are updated with data turning them
on. Recovery is therefore automatic if the transmission
failure is temporary, because the MAX6979 does not
lock up in the watchdog timeout state. The MAX6979
operates correctly when the serial interface is next acti-
vated, and the watchdog circuit is reset and starts
monitoring the serial interface again. The watchdog
function requires no software change to the application
driving the MAX6979.
LED Fault Detection
The MAX6979 includes circuitry that detects open-cir-
cuit LEDs automatically. An open-circuit fault occurs
when an output is programmed to sink current but less
than about 50% of the programmed current flows.
Open circuits are checked just after the falling edge of
OE. The fault data is latched on the rising edge of LE
and is shifted out when new LED data is loaded into the
output latches from the shift register. If one or more out-
put ports are detected with an open-circuit fault, the
D14 and D13 bits of DOUT go high. If no open-circuit
faults are detected, the D14 and D13 are set to low.
The data in the other 14 bit positions in DOUT are not
altered.
Fault status is shifted out on DOUT when the next data
transmission is shifted in after the rising edge of LE. LE
is normally taken high after all 16 bits of new LED data
have been clocked into the shift register(s), and then
DOUT outputs data bit D15. On the next two rising
edges of CLK, the 2 fault status bits, D14 and D13, are
clocked out in that order, followed by the remaining 13
unchanged data bits D12 to D0.
A typical fault-detecting application tests all the-shifted
out data. Bits D0–D12 and D15 are checked against
the originally transmitted data to check data-link integri-
ty. Bits D13 and D14 are checked first to see that they
contain the same data (validating the status) and sec-
ond, whether faults are reported or not by the actual
logic level.
Figure 4 is the LE and CLK to OUT_ timing diagram.
Applications Information
Selecting External Component RSET to
Set LED Output Current
The MAX6979 uses an external resistor RSET to set the
LED current for outputs OUT0–OUT15. The minimum
allowed value of RSET is 327.3Ω, which sets the output
currents to 55mA. The maximum allowed value of RSET
is 1.5kΩ. The reference value, 360Ω, sets the output
currents to 50mA. To set a different output current, use
the formula:
RSET = 18,000/IOUT
where IOUT is the desired output current in mA.
LE
OUT_
LE
OUT_
CLK
OUT_
CLK
OUT_
tCRR
tCRF
tLRR
tLRF
Figure 3. LE and CLK to OUT_ Timing
OE
LE
CLK
DOUT D15 D14 D13 D12
FAULT STATUS BITS
Figure 4. Fault Timing Diagram
Computing Power Dissipation
The upper limit for power dissipation (PD) for the
MAX6979 is determined from the following equation:
PD= (V+ x I+) + (VOUT x DUTY x IOUT x N)
where:
V+ = supply voltage
I+ = operating supply current when sinking IOUT LED
drive current into N outputs
DUTY = PWM duty cycle applied to OE
N = number of MAX6979 outputs driving LEDs at the
same time (maximum is 16)
VOUT = MAX6979 port output voltage when driving load
LED(s)
IOUT = LED drive current programmed by RSET
PD= power dissipation, in mW if currents are in mA
Dissipation example:
IOUT = 47mA, N = 16, DUTY = 1,
VOUT = 2V, V+ = 5.25V
PD= (5.25V x 25mA) + (2V x 1 x 47mA x 16) = 1.776W
Thus, for a 24-pin TSSOP package (TJA = 1/0.0122 =
+82°C/W from the
Absolute Maximum Ratings
), the
maximum allowed ambient temperature TAis given by:
TJ(MAX) = TA+ (PDx TJA) = +150°C =
TA+ (1.776 x 82°C/W)
so TA= +145.6°C.
Overtemperature Cutoff
The MAX6979 contains an internal temperature sensor
that turns off all outputs when the die temperature
exceeds approximately +165°C. The outputs are
enabled again when the die temperature drops below
approximately +140°C. Register contents are not
affected, so when a driver is overdissipating, the exter-
nal symptom is the load LEDs cycling between on and
off as the driver repeatedly overheats and cools, alter-
nately turning the LEDs off and then back on again.
Power-Supply Considerations
The MAX6979 operates with a chip supply V+, and one
or more LED supplies. Bypass each supply to GND
with a 0.1µF capacitor as close to the MAX6979 as pos-
sible. This is normally adequate for static LED driving.
For multiplex or PWM applications, it is necessary to
add an additional bulk electrolytic capacitor of 4.7µF or
more to each supply for every 4 to 16 MAX6979s. The
necessary capacitance depends on the LED load cur-
rent, PWM switching frequency, and serial interface
speed. Inadequate V+ decoupling can cause timing
problems, and very noisy LED supplies can affect LED
current regulation.
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
_______________________________________________________________________________________ 9
L = Low-logic level; H = High-logic level; X = Don’t care; P = Present state; R = Previous state
SHIFT-REGISTER
CONTENTS LATCH CONTENTS OUTPUT CONTENTS
SERIAL
DATA
INPUT
DIN
CLOCK
INPUT
CLK D0D1D2…D
n-1 Dn
LOAD
INPUT
LE D0D1D2…D
n-1 Dn
BLANKING
INPUT
OE D0D1D2…D
n-1 Dn
HHR
1R2…R
n-2 Rn-1 ——————— — — —————
LLR
1R2…R
n-2 Rn-1 ——————— — — —————
XR
0R1R2…R
n-1 Rn——————— — — —————
——
XXX…XX H R0R1R2—R
n-1 Rn— — —————
——P
1P2P3…P
n-1 PnLP0P1P2…P
n-1 PnLP0P1P2…Pn-1Pn
— — —————— — XXX…XX H Hi-Z Hi-Z Hi-Z … Hi-Z Hi-Z
Table 1. 4-Wire Serial-Interface Truth Table
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
10 ______________________________________________________________________________________
PART NO. OF
OUTPUTS
MAX OUTPUT
VOLTAGE (V)
MAX OUTPUT
CURRENT
LED FAULT
DETECTION WATCHDOG
MAX6968 ——
MAX6977 Yes —
MAX6978
8 5.5
Yes Yes
MAX6970 ——
MAX6981 Yes —
MAX6980
836
Yes Yes
MAX6969 ——
MAX6984 Yes —
MAX6979
16 5.5
Yes Yes
MAX6971 ——
MAX6982 Yes —
MAX6983
16 36
55mA
Yes Yes
Selector Guide
Typical Application Circuit
µC
MOSI
OUT0
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
OUT7
SCLK
DIN
CLK
0V
GND
MISO DOUT
360Ω
OEENABLE
+5V
V+
28V
LATCHLOAD
SET
MAX6979
OUT8
OUT9
OUT10
OUT11
OUT12
OUT13
OUT14
OUT15
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
______________________________________________________________________________________ 11
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in
the package code indicates RoHS status only. Package draw-
ings may show a different suffix character, but the drawing per-
tains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE OUTLINE NO. LAND
PATTERN NO.
24 PDIP N24+1 21-0043 —
24 TSSOP U24+1 21-0066 90-0118
MAX6979
16-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 5/05 Initial release —
1 12/10 Updated Ordering Information and Watchdog section 1, 8
