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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.
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