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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

o 25Mb Industry-Standard, 4-Wire Serial Interface at 5V

o 3V to 5.5V Logic Supply

o 16 Constant-Current LED Outputs Rated at 5.5V

o Up to 55mA Continuous Current per Output

o Output Current Programmed by Single Resistor

o 3% Current Matching Between Outputs

o 6% Current Matching Between ICs

o Watchdog Clears Display if Interface Fails

o Reports Open-Circuit LED Faults

o High-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

V+

SET

DOUT

OELE

CLK

DIN

GND

TOP VIEW

OUT15

OUT14

OUT13

OUT12OUT3

OUT2

OUT1

OUT0

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.

Summary of content (12 pages)

PAGE 1
9-3703; Rev 1; 12/10 16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog 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.
PAGE 2
MAX6979 16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog ABSOLUTE MAXIMUM RATINGS 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 ......
PAGE 3
16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog (Typical Operating Circuit, V+ = 4.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.
PAGE 4
16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog MAX6979 3.3V TIMING CHARACTERISTICS (Typical Operating Circuit, V+ = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.
PAGE 5
16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 720Ω, V+ = 3.3V) 16 TA = +25°C 14 TA = -40°C 20 TA = +85°C 15 TA = +125°C 10 5 12 0 3.0 3.5 4.0 4.5 5.0 50 TA = -40°C 40 TA = +25°C TA = +85°C 30 TA = +125°C 20 10 TA = -40°C 10 0 0 5.5 0.5 1.0 1.5 2.0 2.5 3.0 0 0.5 1.0 1.5 2.0 2.5 3.0 SUPPLY VOLTAGE (V) PORT OUTPUT VOLTAGE (V) PORT OUTPUT VOLTAGE (V) PORT OUTPUT CURRENT vs.
PAGE 6
16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog MAX6979 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. 4 LE 5–20 OUT0– OUT15 21 OE 22 DOUT 23 SET LED Current Setting. Connect SET to GND through a resistor (RSET) to set the maximum LED current.
PAGE 7
16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog tCL tCH tLS tCP MAX6979 LE tLW tLF CLK tDH tDS DIN D15 D14 D1 D0 tDO D15 DOUT tOEW OE tOEL tOEH . 80% OUT_ 20% tf tr Figure 2. 4-Wire Serial-Interface Timing Diagram The 4-wire serial interface comprises a 16-bit shift register 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.
PAGE 8
MAX6979 16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog OE LE tLRF OUT_ LE CLK DOUT D14 D13 D15 D12 LE tLRR FAULT STATUS BITS OUT_ Figure 4. Fault Timing Diagram CLK tCRF OUT_ CLK tCRR OUT_ Figure 3. LE and CLK to OUT_ Timing Watchdog The MAX6979 includes a watchdog circuit that monitors the CLK, DIN, and LE inputs.
PAGE 9
16-Port, 5.
PAGE 10
16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog MAX6979 Selector Guide PART NO. OF OUTPUTS MAX OUTPUT VOLTAGE (V) 8 5.5 MAX OUTPUT CURRENT MAX6968 LED FAULT DETECTION WATCHDOG — — Yes — MAX6978 Yes Yes MAX6970 — — Yes — Yes Yes — — Yes — MAX6979 Yes Yes MAX6971 — — MAX6977 8 MAX6981 36 MAX6980 55mA MAX6969 16 MAX6984 16 MAX6982 5.
PAGE 11
16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog PROCESS: BiCMOS 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 drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
PAGE 12
MAX6979 16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog Revision History REVISION NUMBER REVISION DATE 0 5/05 Initial release 1 12/10 Updated Ordering Information and Watchdog section DESCRIPTION PAGES CHANGED — 1, 8 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.