Editor's note: Maxim has recently introduced the MAX6977 driver family with LED fault detection. The MAX6977 serial interface LED driver provides eight open-drain, constant-current sinking, 5.5V LED driver outputs, and operates from a 3V to 5.5V supply. The MAX6977 and LED supplies can be powered up in any order, and all constant current outputs are set by an external resistor, up to 55mA each. This series of products uses 25Mb, industrial standard 4-wire serial port for control. The MAX6977 includes an LED open-circuit automatic detection circuit. The fault state is loaded into the serial port shift register when LE is set high, and is shifted out by DOUT when the next data is shifted in. The MAX6977 uses industry-standard shift registers plus latched serial ports. Data is shifted into the 8-bit shift register of the driver through data input DIN and clock input CLK. After 8 clock cycles, the input data appears on the output DOUT. This mode of operation allows multiple MAX6977s to be cascaded. The latch enable input LE loads the 8-bit data of the shift register into the 8-bit output latch to determine the LED switch. The output enable input / OE controls all eight outputs of the switch, and its fast response characteristics are suitable as a PWM input to control the brightness of the LED. The MAX6977 family of shift registers plus latched LED drivers are available in 12 models. The series is available in 8-port and 16-port versions with 5.5V or 36V rated LED output, and some models feature LED open-circuit detection and watchdog functionality. All models are powered from a 3V to 5.5V supply and operate over the -40°C to +125°C temperature range. Mainly used in architectural lighting systems, game functions, Marquee displays, order management lights, traffic lights and signal lights. Pricing and availability can now be ordered from Maxim's, with a unit price of $1.10 for 1k.
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