MAX6978 Datasheet, PDF (1/13 Pages) Maxim Integrated Products – 8-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog

19-3578; Rev 1; 3/05
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
General Description
The MAX6978 serial-interfaced LED driver provides
eight open-drain, constant-current sinking LED driver
outputs rated at 5.5V. The MAX6978 operates from a 3V
to 5.5V supply. The MAX6978 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 MAX6978 operates with a
25Mb, industry-standard, 4-wire serial interface.
The MAX6978 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 MAX6978 includes a fail-safe feature for safety-
related applications, which blanks the display if the ser-
ial 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 auto-
matic if the transmission failure is temporary. The
watchdog function requires no software change to the
application driving the MAX6978.
The MAX6978 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 MAX6978s. 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 output-
enable input OE gates all eight outputs on and off, and
is fast enough to be used as a PWM input for LED
intensity control.
The MAX6978 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.
Variable Message Signs
Marquee Displays
Point-of-Order Signs
Traffic Signs
Gaming Features
Architectural Lighting
Applications
Features
♦ 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
♦ Watchdog Clears Display if Interface Fails
♦ Reports Open-Circuit LED Faults
♦ -40°C to +125°C Temperature Range
Ordering Information
PART
TEMP RANGE
MAX6978AUE
-40°C to +125°C
MAX6978APE
-40°C to +125°C
MAX6978AEE
-40°C to +125°C
*EP = Exposed pad.
PIN-PACKAGE
16 TSSOP-EP*
16 PDIP
16 SSOP
Typical Application Circuit and Selector Guide appear at
end of data sheet.
Pin Configuration
TOP VIEW
GND ₁
DIN 2
CLK 3
LE 4
OUT0 5
OUT1 6
OUT2 7
OUT3 8
MAX6978AUE
MAX6978APE
MAX6978AEE
16 V+
15 SET
14 DOUT
13 OE
12 OUT7
11 OUT6
10 OUT5
9 OUT4
TSSOP/PDIP/SSOP
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