MAX6978 19-3578 Rev 2 7/05 8-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog General Description Features The MAX6978 serial-interfaced LED driver provides 25Mb Industry-Standard 4-Wire Serial Interface at 5V eight open-drain, constant-current sinking LED driver 3V to 5.5V Logic Supply outputs rated at 5.5V. The MAX6978 operates from a 3V to 5.5V supply. The MAX6978 supply and the LEDs 8 Constant-Current LED Outputs Rated at 5.5V supply can power up in any order. The constant-current Up to 55mA Continuous Current per Output outputs are programmed together to up to 55mA using a single external resistor. The MAX6978 operates with a Output Current Programmed by Single Resistor 25Mb, industry-standard, 4-wire serial interface. 3% Current Matching Between Outputs The MAX6978 includes circuitry that automatically detects open-circuit LEDs. Fault status is loaded into the 6% Current Matching Between ICs serial-interface shift register when LE goes high and is Watchdog Clears Display if Interface Fails automatically shifted out on DOUT when the next data transmission is shifted in. Reports Open-Circuit LED Faults The MAX6978 includes a fail-safe feature for safety- -40C to +125C Temperature Range 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 Ordering Information automatically cleared. This turns off all LEDs connected to the outputs. The shift register data is not disturbed. PART TEMP RANGE PIN-PACKAGE The outputs remain off until the driver output latches are MAX6978AUE -40C to +125C 16 TSSOP-EP* updated with data turning them on, so recovery is auto- MAX6978APE -40C to +125C 16 PDIP matic if the transmission failure is temporary. The watchdog function requires no software change to the MAX6978AAE -40C to +125C 16 SSOP application driving the MAX6978. *EP = Exposed pad. 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 Typical Application Circuit and Selector Guide appear at DOUT eight clock cycles later to allow cascading of end of data sheet. 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- Pin Configuration 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. TOP VIEW The MAX6978 is one of a family of 12 shift-register-plus- GND latch-type LED drivers. The family includes 8-port and 1 16 V+ 16-port types, with 5.5V- or 36V-rated LED outputs, with DIN 2 15 SET and without open-circuit LED detection and watchdog. CLK 3 14 DOUT All versions operate from a 3V to 5.5V supply, and are specified over the -40C to +125C temperature range. LE 4 MAX6978AUE 13 OE MAX6978APE OUT0 5 12 OUT7 MAX6978AAE Applications OUT1 6 11 OUT6 Variable Message Signs OUT2 7 10 OUT5 Marquee Displays OUT3 8 9 OUT4 Point-of-Order Signs Traffic Signs TSSOP/PDIP/SSOP Gaming Features Architectural Lighting Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct at 1-888-629-4642, or visit Maxims website at www.maxim-ic.com.8-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog ABSOLUTE MAXIMUM RATINGS Voltage (with respect to GND) Continuous Power Dissipation (T = +70C) A V+ ............................................................................-0.3V to +6V 16-Pin SSOP (derate 7.1mW/C above +70C) ............571mW OUT .......................................................................-0.3V to +6V 16-Pin PDIP (derate 10.5mW/C above +70C)............842mW DIN, CLK, LE, OE, SET ................................-0.3V to (V+ + 0.3V) 16-Pin TSSOP (derate 21.3mW/C over DOUT Current ..................................................................10mA T = +70C) ..............................................................1702mW A OUT Sink Current .............................................................60mA Operating Temperature Range .........................-40C to +125C Total GND Current ...........................................................480mA Junction Temperature......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (Typical Operating Circuit, V+ = 3V to 5.5V, T = T to T , unless otherwise noted. Typical values are at V+ = 5V, T = +25C.) A MIN MAX A (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Operating Supply Voltage V+ 3.0 5.5 V Output Voltage V 5.5 V OUT Standby Current All logic inputs at V+ or GND, DOUT (Interface Idle, All Output Ports I 4.5 5.6 mA + unloaded High Impedance, R = 360 ) SET Standby Current (Interface Running, All Output f = 5MHz, OE = V+, DIN and LE = V+ CLK I 4.7 6 mA + Ports High Impedance, or GND, DOUT unloaded R = 360 ) SET Supply Current All logic inputs at V+ or GND, (Interface Idle, All Output Ports I 10 25 mA + DOUT unloaded Active Low, R = 360 ) SET Input High Voltage V 0.7 V+ V IH DIN, CLK, LE, OE Input Low Voltage V 0.3 V+ V IL DIN, CLK, LE, OE Hysteresis Voltage V 0.8 V I DIN, CLK, LE, OE Input Leakage Current I , I -1 +1 A IH IL DIN, CLK, LE, OE V + Output-High Voltage DOUT V I = 4mA V OH SOURCE - 0.5V Output Low Voltage V I = 4mA 0.5 V OL SINK Output Current V+ = 3V to 5.5V, V = 0.8V to 2.5V, OUT I 42 50 56 mA OUT OUT R = 360 SET Output Leakage Current OUT I OE = V+, V = V+ 1 A LEAK OUT Watchdog Timeout t 1s WD 2 MAX6978