Description

The MAX6979 serial-interfaced LED driver provides 16open-drain, constant-current-sinking LED driver outputsrated at 5.5V. The MAX6979 operates from a 3V to 5.5Vsupply. The MAX6979 supply and the LEDs' supply canpower up in any order. The constant-current outputsare programmed together to up to 55mA using a singleexternal resistor. The MAX6979 operates with a 25Mb,industry-standard, 4-wire serial interface.The MAX6979 includes circuitry that automaticallydetects open-circuit LEDs. Fault status is loaded into theserial-interface shift register when LE goes high and isautomatically shifted out on DOUT when the next datatransmission is shifted in.The MAX6979 includes a fail-safe feature for safety-relatedapplications, which blanks the display if the serialinterface fails. If the serial interface becomesinactive for more than 1s, all driver output latches areautomatically cleared. This turns off all LEDs connectedto the outputs. The shift register data is not disturbed.The outputs remain off until the driver output latches areupdated with data turning them on, so recovery is automaticif the transmission failure is temporary. Thewatchdog function requires no software change to theapplication driving the MAX6979.The MAX6979 uses the industry-standard shift-register-plus-latch-type serial interface. The driver accepts datashifted into a 16-bit shift register using data input DINand clock input CLK. Input data appears at the outputDOUT 16 clock cycles later to allow cascading of multipleMAX6979s. The latch-enable input, LE, loads the 16bits of shift-register data into a 16-bit output latch to setwhich LEDs are on and which are off. The output-enableinput, OE-bar, gates all 16 outputs on and off, and isfast enough to be used as a PWM input for LED intensitycontrol.The MAX6979 is one of a family of 12 shift-register-plus-latch-type LED drivers. The family includes 8-port and16-port types, with 5.5V- or 36V-rated LED outputs, withand without open-circuit LED detection and watchdog.All versions operate from a 3V to 5.5V supply, and arespecified over the -40°C to +125°C temperature range.ApplicationsArchitectural LightingGaming FeaturesMarquee DisplaysPoint-of-Order SignsTraffic SignsVariable Message Signs