MAX6978

♦ 25Mb Industry-Standard 4-Wire Serial Interface at 5V
♦ 3V to 5.5V Logic Supply
♦ 8 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
♦ -40°C to +125°C Temperature Range

Variable Message Signs
Marquee Displays
Point-of-Order Signs
Traffic Signs
Gaming Features
Architectural Lighting

Voltage (with respect to GND)
V+ ............................................................................-0.3V to +6V
OUT_ .......................................................................-0.3V to +6V
DIN, CLK, LE, OE, SET ..................................-0.3V to (V+ + 0.3V)
DOUT Current ..................................................................±10mA
OUT_ Sink Current ..............................................................60mA
Total GND Current .............................................................480mA
Continuous Power Dissipation
  16-Pin SSOP (derate 7.1mW/°C over T_A = +70°C)........571mW
  16-Pin PDIP (derate 10.5mW/°C over T_A = +70°C) ......842mW
  16-Pin TSSOP (derate 21.3mW/°C over
  T_A = +70°C) .................................................................1702mW
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

The MAX6978 serial-interfaced LED driver provides eight open-drain, constant-current sinking LED driver outputs rated at 5.5V. The MAX6978 operates from a 3V to 5.5V supply. The MAX6978 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 MAX6978 operates with a 25Mb, industry-standard, 4-wire serial interface.

The MAX6978 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 MAX6978 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 MAX6978.

The MAX6978 uses the industry-standard shift-registerplus- latch-type serial interface. The driver accepts data shifted into an 8-bit shift register using data input DIN
and clock input CLK. Input data appears at the output DOUT eight clock cycles later to allow cascading of multiple MAX6978s. The latch-enable input LE loads the 8 bits of shift-register data into an 8-bit output latch to set which LEDs are on and which are off. The outputenable input OE gates all eight outputs on and off, and is fast enough to be used as a PWM input for LED intensity control.

The MAX6978 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 of MAX6978 operate from a 3V to 5.5V supply, and are specified over the -40°C to +125°C temperature range.