MAX6979 16-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog

LED Fault Detection, and Watchdog Timer

Status

Active: In Production.

Description

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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 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-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 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 output-enable input, OE-bar, 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-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.

Key Features		Applications/Uses
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		Architectural Lighting Gaming Features Marquee Displays Point-of-Order Signs Traffic Signs Variable Message Signs