MAX6977 8-Port, 5.5V Constant-Current LED Driver with LED Fault Detection

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The MAX6977 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 MAX6977 uses the industry-standard shift-register-plus- 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 MAX6977s. 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-bar gates all eight outputs on and off, and is fast enough to be used as a PWM input for LED intensity control.

For safety-related applications requiring a watchdog timer, refer to the MAX6978 data sheet that includes a fail-safe feature that blanks the display if the serial interface becomes inactive for more than 1s.

The MAX6977 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¡ãC to +125¡ãC temperature range.

• 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
• Reports Open-Circuit LED Faults
• -40¡ãC to +125¡ãC Temperature Range

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