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The MAX6977 serial-interfaced LED driver provides
eight open-drain, constant-current sinking LED driver
outputs rated at 5.5V. The MAX6977 operates from a 3V
to 5.5V supply. The MAX6977 supply and the LEDs'
supply may power up in any order. The constant-current
outputs are programmed together to up to 55mA
using a single external resistor. The MAX6977 operates
with a 25Mb, industry-standard, 4-wire serial interface.
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°C to +125°C temperature range.
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