MAXIM MAX6979 User Manual

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 safety­related applications, which blanks the display if the ser­ial 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 auto­matic 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-register­plus-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 multi­ple 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 output­enable input, OE, gates all 16 outputs on and off, and is
fast enough to be used as a PWM input for LED intensi­ty control.

The MAX6979 is one of a family of 12 shift-register-plus­latch-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

♦ 25Mb Industry-Standard, 4-Wire Serial Interface at 5V
♦ 3V to 5.5V Logic Supply
♦ 16 Constant-Current LED Outputs Rated at 5.5V
♦ Up to 55mA Continuous Current per Output
♦ Output Current Programmed by Single Resistor
♦ 3% Current Matching Between Outputs
♦ 6% Current Matching Between ICs
♦ Watchdog Clears Display if Interface Fails
♦ Reports Open-Circuit LED Faults
♦ High-Dissipation, 24-Pin Packages
♦ -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 0; 5/05

For pricing, delivery, and ordering information, please contact Maxim/Dallas 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

PIN­PACKAGE

PK G

C O D E

MAX6979AUG

24 TSSOP —

MAX6979APG

24 PDIP —

-40°C to +125°C

-40°C to +125°C

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

ELECTRICAL CHARACTERISTICS

(Typical Operating Circuit, V+ = 3V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at V+ = 5V, TA= +25°C.)

(Note 1)

PARAMETER

CONDITIONS

UNITS

Operating Supply Voltage V+ 3.0 5.5 V

Output Voltage V

OUT

5.5 V

Standby Current
(Interface Idle, All Output Ports
High Impedance, R

SET

= 360Ω)

I

+

All logic inputs at V+ or GND, DOUT
unloaded

5.7 8 mA

Standby Current
(Interface Running, All Output
Ports High Impedance,
R

SET

= 360Ω)

I

+

f

CLK

= 5MHz, OE = V+, DIN and LE = V+

or GND, DOUT unloaded

6 8.5 mA

Supply Current
(Interface Idle, All Output Ports
Active Low, R

SET

= 360Ω)

I

+

All logic inputs at V+ or GND,
DOUT unloaded

18 25 mA

Input High Voltage
DIN, CLK, LE, OE

V

IH

0.7 x
V+

V

Input Low Voltage
DIN, CLK, LE, OE

V

IL

0.3 x
V+

V

Hysteresis Voltage
DIN, CLK, LE, OE

∆V

I

0.8 V

Input Leakage Current
DIN, CLK, LE, OE

I

IH

, I

IL

-1 +1 µA

Output High Voltage DOUT V

OH

I

SOURCE

= 4mA

V +

V

Output Low Voltage V

OL

I

SINK

= 4mA 0.5 V

Output Current OUT I

OUT

V+ = 3V to 5.5V, V

OUT

= 0.5V to 2.5V,

R

SET

= 360Ω

37 50 61 mA

Output Leakage Current OUT I

LEAK

OE = V+, V

OUT

= V+ 1 µA

Watchdog Timeout t

WD

0.1 1 2.5 s

SYMBOL

MIN TYP MAX

- 0.5V

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= T

MIN

to T

MAX

, unless otherwise noted.) (Notes 1, 2)

PARAMETER

CONDITIONS

UNITS

CLK Clock Period t

CP

40 ns

CLK Pulse-Width High t

CH

19 ns

CLK Pulse-Width Low t

CL

19 ns

DIN Setup Time t

DS

4ns

DIN Hold Time t

DH

8ns

DOUT Propagation Delay t

DO

12 32 ns

DOUT Rise and Fall Time

C

DOUT

= 10pF, 20% to 80% 10 ns

LE Setup Time t

LS

10 ns

LE Rising to OUT Rising Delay t

LRR

(Note 2) 100 ns

LE Rising to OUT Falling Delay t

LRF

(Note 2) 300 ns

C LK Ri si ng to O U T Ri si ng D el ay t

CRR

(Note 2) 100 ns

C LK Ri si ng to O U T Fal l i ng D el ay t

CRF

(Note 2) 310 ns

OE Rising to OUT Rising Delay t

OEH

100 ns

OE Falling to OUT Falling Delay t

OEL

320 ns

LED Output OUT Turn-On Fall
Time

t

f

80% to 20%; pullup resistor = 65Ω 120 ns

LED Output OUT Turn-Off Rise
Time

t

r

20% to 80%; pullup resistor = 65Ω 120 ns

SYMBOL

tDR, t

DF

MIN TYP MAX

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,

R

SET

= 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°C

TA = +85°C

TA = -40°C

TA = +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°C

TA = +85°C

TA = -40°C

SUPPLY CURRENT vs. SUPPLY VOLTAGE

(INTERFACE IDLE, ALL OUTPUTS OFF,

R

SET

= 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,

R

SET

= 720Ω)

TA = +125°C

TA = +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= T

MIN

to T

MAX

, unless otherwise noted.) (Notes 1, 2)

PARAMETER

CONDITIONS

UNITS

CLK Clock Period t

CP

52 ns

CLK Pulse-Width High t

CH

24 ns

CLK Pulse-Width Low t

CL

24 ns

DIN Setup Time t

DS

4ns

DIN Hold Time t

DH

8ns

DOUT Propagation Delay t

DO

12 50 ns

DOUT Rise and Fall Time C

DOUT

= 10pF, 20% to 80% 12 ns

LE Setup Time t

LS

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 t

OEH

120 ns

OE Falling to OUT Falling Delay t

OEL

330 ns

LED Output OUT Turn-On Fall
Time

t

f

80% to 20% 120 ns

LED Output OUT Turn-Off Rise
Time

t

r

20% to 80% 120 ns

Note 1: All parameters tested at TA= +25°C. Specifications over temperature are guaranteed by design.
Note 2: See Figure 3.

SYMBOL

MIN TYP MAX