19-3808; Rev 0; 7/05 16-Port, 36V Constant-Current LED Driver The MAX6971 serial-interfaced LED driver provides 16 open-drain, constant-current-sinking LED driver outputs rated at 36V. The MAX6971 operates from a 3V to 5.5V supply. The MAX6971 supply and the LEDs’ supply or supplies can power up in any order. The constant-current outputs are programmed together to up to 55mA using a single external resistor. The MAX6971 operates with a 25Mb, industry-standard, 4-wire serial interface. The MAX6971 uses the industry-standard, shift-registerplus-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 DOUT output 16 clock cycles later to allow cascading of multiple MAX6971s. 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 outputenable, OE, gates all 16 outputs on and off, and is fast enough to be used as a PWM input for LED intensity control. For applications requiring LED fault detection, refer to the MAX6983*, which automatically detects open-circuit LEDs. For safety-related applications requiring a watchdog timer, refer to the MAX6983, which includes a fail-safe feature that blanks the display if the serial interface becomes inactive for more than 1s. The MAX6971 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. Applications Variable Message Signs Features ♦ 25Mb, Industry-Standard, 4-Wire Serial Interface ♦ 3V to 5.5V Logic Supply ♦ 16 Constant-Current LED Outputs Rated at 36V ♦ Up to 55mA Continuous Current per Output ♦ Output Current Programmed by Single Resistor ♦ 3% Current Matching Between Outputs ♦ 6% Current Matching Between ICs ♦ High-Dissipation, 24-Pin Packages ♦ -40°C to +125°C Temperature Range Ordering Information PART TEMP RANGE -40°C to +125°C 24 TSSOP MAX6971ANG -40°C to +125°C 24 Narrow PDIP Typical Application Circuit and Selector Guide appear at end of data sheet. Pin Configuration TOP VIEW GND 1 24 V+ DIN 2 23 SET CLK 3 22 DOUT LE 4 OUT0 5 Marquee Displays PIN-PACKAGE MAX6971AUG 21 OE MAX6971AUG MAX6971ANG 20 OUT15 OUT1 6 19 OUT14 Point-of-Order Signs OUT2 7 18 OUT13 Traffic Signs OUT3 8 17 OUT12 Gaming Features OUT4 9 16 OUT11 Architectural Lighting OUT5 10 15 OUT10 OUT6 11 14 OUT9 OUT7 12 13 OUT8 *Future product—contact factory for availability. TSSOP/PDIP ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX6971 General Description MAX6971 16-Port, 36V Constant-Current LED Driver ABSOLUTE MAXIMUM RATINGS Voltage with respect to GND. V+ ............................................................................-0.3V to +6V OUT_ .....................................................................-0.3V to +40V DIN, CLK, LE, OE, SET ................................-0.3V to (V+ + 0.3V) DOUT Current ..................................................................±10mA OUT_ Sink Current .............................................................60mA Total GND Current ...........................................................960mA Continuous Power Dissipation (TA = +70°C) 24-Pin TSSOP (derate 12.2mW/°C over +70°C) ..........975mW 24-Pin PDIP (derate 13.3mW/°C over +70°C)............1067mW Operating Temperature Range .........................-40°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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, TA = TMIN to TMAX, unless otherwise noted. Typical values are at V+ = 5V, TA = +25°C.) (Note 1) PARAMETER Operating Supply Voltage Output Voltage SYMBOL CONDITIONS V+ MIN TYP MAX UNITS 5.5 V 36 V 5.7 8 mA 3.0 VOUT Standby Current (Interface Idle, All Output Ports High Impedance, RSET = 360Ω) I+ All logic inputs at V+ or GND, DOUT unloaded Standby Current (Interface Running, All Output Ports High Impedance, RSET = 360Ω) I+ fCLK = 5MHz, OE = V+, DIN and LE = V+ or GND, DOUT unloaded 6 8.5 mA Supply Current (Interface Idle, All Output Ports Active Low, RSET = 360Ω) I+ All logic inputs at V+ or GND, DOUT unloaded 18 25 mA Input High Voltage DIN, CLK, LE, OE VIH Input Low Voltage DIN, CLK, LE, OE VIL Hysteresis Voltage DIN, CLK, LE, OE ∆VI Input Leakage Current DIN, CLK, LE, OE 0.7 x V+ V 0.3 x V+ 0.8 IIH, IIL -1 Output High-Voltage DOUT VOH ISOURCE = 4mA Output Low Voltage VOL ISINK = 4mA Output Current OUT_ IOUT V+ = 3V to 5.5V, VOUT = 0.8V to 2.5V, RSET = 360Ω Output Leakage Current OUT_ ILEAK OE = V+ +1 µA V 50 Note 1: All parameters tested at TA = +25°C. Specifications over temperature are guaranteed by design. 2 V V+ - 0.5V 37 V _______________________________________________________________________________________ 0.5 V 61 mA 1 µA 16-Port, 36V Constant-Current LED Driver (Typical Operating Circuit, V+ = 4.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Notes 1, 2, 3) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CLK Clock Period tCP 40 ns CLK Pulse-Width High tCH 19 ns CLK Pulse-Width Low tCL 19 ns DIN Setup Time tDS 4 ns DIN Hold Time tDH 8 ns DOUT Propagation Delay tDO DOUT Rise and Fall Time tDR, tDF LE Pulse-Width High LE Setup Time 12 CDOUT = 10pF, 20% to 80% tLW 32 10 20 tLS ns ns ns 10 ns LE Rising to OUT_ Rising Delay tLRR (Note 3) 100 ns LE Rising to OUT_ Falling Delay tLRF (Note 3) 300 ns CLK Rising to OUT_ Rising Delay tCRR (Note 3) 100 ns CLK Rising to OUT_ Falling Delay tCRF (Note 3) 310 ns OE Rising to OUT_ Rising Delay tOEH (Note 3) 100 ns OE Falling to OUT_ Falling Delay tOEL (Note 3) 320 ns LED Output OUT_ Turn-On Fall Time tf 80% to 20%, pullup resistor = 65Ω 120 ns LED Output OUT_ Turn-Off Rise Time tr 20% to 80%, pullup resistor = 65Ω 120 ns Note 1: All parameters tested at TA = +25°C. Specifications over temperature are guaranteed by design. Note 2: See Figure 3. Note 3: A 65Ω pullup resistor connected from OUT_ to 5.5V. _______________________________________________________________________________________ 3 MAX6971 5V TIMING CHARACTERISTICS 3.3V TIMING CHARACTERISTICS (Typical Operating Circuit, V+ = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CLK Clock Period tCP 52 ns CLK Pulse-Width High tCH 24 ns CLK Pulse-Width Low tCL 24 ns DIN Setup Time tDS 4 ns DIN Hold Time tDH 8 DOUT Propagation Delay tDO 12 DOUT Rise and Fall Time tDR, tDF ns 50 CDOUT = 10pF, 20% to 80% ns 12 ns LE Pulse-Width High tLW 20 ns LE Setup Time tLS 15 ns LE Rising to OUT_ Rising Delay tLRR (Note 3) 120 ns LE Rising to OUT_ Falling Delay tLRF (Note 3) 310 ns CLK Rising to OUT_ Rising Delay tCRR (Note 3) 120 ns CLK Rising to OUT_ Falling Delay tCRF (Note 3) 330 ns OE Rising to OUT_ Rising Delay tOEH (Note 3) 120 ns OE Falling to OUT_ Falling Delay tOEL (Note 3) 330 ns LED Output OUT_ Turn-On Fall Time tf 80% to 20% (Note 3) 120 ns LED Output OUT_ Turn-Off Rise Time tr 20% to 80% (Note 3) 120 ns Note 1: All parameters tested at TA = +25°C. Specifications over temperature are guaranteed by design. Note 2: See Figure 3. Note 3: A 65Ω pullup resistor connected from OUT_ to 5.5V. Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) SUPPLY CURRENT (mA) 1.95 1.90 TA = +25°C TA = -40°C 1.85 3.65 TA = +125°C TA = +85°C 3.60 3.55 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 4 5.0 5.5 35 30 25 TA = +25°C 20 15 10 3.50 3.0 TA = +85°C TA = +125°C TA = -40°C TA = +25°C TA = -40°C 1.80 40 MAX6971 toc03 TA = +85°C SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS ON, RSET = 720Ω) SUPPLY CURRENT (mA) TA = +125°C 3.70 SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS OFF, RSET = 360Ω) MAX6971 toc02 SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS OFF, RSET = 720Ω) MAX6971 toc01 2.00 SUPPLY CURRENT (mA) MAX6971 16-Port, 36V Constant-Current LED Driver 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 5.0 5.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 5.0 5.5 16-Port, 36V Constant-Current LED Driver TA = +25°C 25 20 20 TA = +25°C 15 TA = +85°C TA = +125°C 10 5 TA = -40°C 3.0 3.5 4.0 4.5 5.0 MAX6971 toc06 TA = +25°C 40 TA = +85°C 30 TA = +125°C 20 0 0 5.5 TA = -40°C 50 10 0 15 0.5 1.0 1.5 2.0 2.5 3.0 0 0.5 1.0 1.5 2.0 2.5 3.0 SUPPLY VOLTAGE (V) PORT OUTPUT VOLTAGE (V) PORT OUTPUT VOLTAGE (V) PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 720Ω, V+ = 5.0V) PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 360Ω, V+ = 5.0V) PORT OUTPUT CURRENT vs. SUPPLY VOLTAGE (RSET = 720Ω, VOUT = 2V) 20 TA = +25°C TA = +85°C 15 TA = +125°C 10 TA = -40°C 5 50 40 TA = +25°C 30 TA = +85°C TA = +125°C 20 25.0 PORT OUTPUT CURRENT (mA) 25 60 MAX6971 toc08 TA = -40°C PORT OUTPUT CURRENT (mA) MAX6971 toc07 30 TA = +85°C 24.5 TA = +125°C 24.0 TA = +25°C TA = -40°C 23.5 10 0 0 0.5 1.0 1.5 2.0 2.5 3.0 23.0 0 0.5 PORT OUTPUT VOLTAGE (V) 1.0 1.5 2.0 2.5 3.0 3.0 3.5 PORT OUTPUT VOLTAGE (V) TA = -40°C 47 5.0 5.5 PORT OUTPUT CURRENT vs. RSET RESISTANCE (V+ = 5.0V) TA = +25°C 48 4.5 TA = +85°C TA = +125°C 46 50 MAX6971 toc11 49 4.0 SUPPLY VOLTAGE (V) PORT OUTPUT CURRENT vs. SUPPLY VOLTAGE (RSET = 360Ω, VOUT = 2V) MAX6971 toc10 0 PORT OUTPUT CURRENT (mA) PORT OUTPUT CURRENT (mA) 60 MAX6971 toc09 30 25 PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 360Ω, V+ = 3.3V) PORT OUTPUT CURRENT (mA) 35 TA = -40°C PORT OUTPUT CURRENT (mA) SUPPLY CURRENT (mA) TA = +125°C 30 MAX6971 toc05 TA = +85°C 40 PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 720Ω, V+ = 3.3V) PORT OUTPUT CURRENT (mA) 45 MAX6971 toc04 SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS ON, RSET = 360Ω) 40 30 20 10 0 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 5.0 5.5 0 1 2 3 4 5 RSET RESISTANCE (kΩ) _______________________________________________________________________________________ 5 MAX6971 Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) 16-Port, 36V Constant-Current LED Driver MAX6971 Pin Description PIN NAME 1 GND Ground FUNCTION 2 DIN Serial-Data Input. Data is loaded into the internal 16-bit shift register on CLK’s rising edge. 3 CLK Serial-Clock Input. Data is loaded into the internal 16-bit shift register on CLK’s rising edge. 4 LE 5–20 OUT0–OUT15 21 OE Output-Enable Input. High forces outputs OUT0 to OUT15 high impedance, without altering the contents of the output latches. Low enables outputs OUT0 to OUT15 to follow the state of the output latches. 22 DOUT Serial-Data Output. Data is clocked out of the 16-bit internal shift register to DOUT on CLK’s rising edge. 23 SET LED Current Setting. Connect SET to GND through a resistor (RSET) to set the maximum LED current. 24 V+ Positive Supply Voltage. Bypass V+ to GND with a 0.1µF ceramic capacitor. Load-Enable Input. Data is loaded transparently from the internal shift register(s) to the output latch(es) while LE is high. Data is latched into the output latch(es) on LE’s falling edge, and retained while LE is low. LED Driver Outputs. OUT0 to OUT15 are open-drain, constant-current-sinking outputs rated to 28V. CLK MAX6971 DIN D0 SERIAL-TO-PARALLEL SHIFT REGISTER D15 LE D0 LATCHES D15 DOUT POWER-ON RESET V+ OE V+ CONSTANT-CURRENT SINKS D0 D15 CURRENT REFERENCE RSET OUT0 OUT2 OUT1 OUT3 OUT15 OUT4 GND GND Figure 1. Block Diagram 6 _______________________________________________________________________________________ 16-Port, 36V Constant-Current LED Driver The MAX6971 LED driver comprises a 4-wire serial interface driving 16 constant-current-sinking, opendrain output ports. The outputs drive LEDs in either static or multiplex applications (Figure 1). The constantcurrent outputs are guaranteed for current accuracy not only with chip-supply voltage variations (5V ±10% and 3V to 5.5V), but also over a realistic range of driver output voltage drop (0.8V to 2.5V). The drivers use current-sensing feedback circuitry (not simple current mirrors) to ensure very small current variations over the full allowed range of output voltage (see the Typical Operating Characteristics). The 4-wire serial interface comprises a 16-bit shift register and a 16-bit transparent latch. The shift register is written through a clock input, CLK, and a data input, DIN, and the data propagates to a data output, DOUT. The data output allows multiple drivers to be cascaded and operated together. The contents of the 16-bit shift register are loaded into the transparent latch through a latch-enable input, LE. The latch is transparent to the shift register outputs when high, and latches the current state on the falling edge of LE. Each driver output is an open-drain, constant-current sink that should be connected to the cathode of either a single LED or a series string of multiple LEDs. The LED anode can be connected to a supply voltage of up to 36V, independent of the MAX6971 supply, V+. The constant-current capability is up to 55mA per output, set for all eight outputs by an external resistor, RSET. 4-Wire Serial Interface The serial interface on the MAX6971 is a 4-wire serial interface using four inputs (DIN, CLK, LE, OE) and a data output (DOUT). This interface is used to write display data to the MAX6971. The serial-interface data word length is 16 bits, D0–D15. See Figure 2. The functions of the five interface pins are as follows. DIN is the serial-data input, and must be stable when it is sampled on the rising edge of CLK. Data is shifted in, MSB first. This means that data bit D15 is clocked in first, followed by 15 more data bits finishing with the LSB, D0. LE tCL tCH tLS tCP tLW tLF CLK tDH tDS DIN D15 D14 D1 D0 tDO D7 DOUT tOEW OE tOEL tOEH . 80% OUT_ 20% tf tr Figure 2. 4-Wire Serial-Interface Timing Diagram _______________________________________________________________________________________ 7 MAX6971 Detailed Description 16-Port, 36V Constant-Current LED Driver MAX6971 CLK is the serial-clock input, which shifts data at DIN into the MAX6971 16-bit shift register on its rising edge. LE LE is the latch load input of the MAX6971 that transfers data from the MAX6971 16-bit shift register to its 16-bit latch when LE is high (transparent latch), and latches the data on the falling edge of LE (Figure 2). The fourth input provides output-enable control of the output drivers. OE is high to force outputs OUT0–OUT15 high impedance, without altering the contents of the output latches, and low to enable outputs OUT0–OUT15 to follow the state of the output latches. OE is independent of the operation of the serial interface. Data can be shifted into the serial-interface shift register and latched, regardless of the state of OE. DOUT is the serial-data output, which shifts data out from the MAX6971’s 16-bit shift register on the rising edge of CLK. Data at DIN is propagated through the shift register and appears at DOUT 16 clock cycles later. tLRF OUT_ LE tLRR OUT_ CLK tCRF OUT_ CLK tCRR OUT_ Figure 3. LE and CLK to OUT_ Timing Table 1. 4-Wire Serial-Interface Truth Table SERIAL CLOCK DATA INPUT INPUT CLK D0 DIN SHIFT-REGISTER CONTENTS D1 D2 LOAD INPUT LE … Dn-1 Dn LATCH CONTENTS D0 D1 D2 OUTPUT CONTENTS BLANKING INPUT OE … Dn-1 Dn D0 D1 D2 … Dn-1 Dn H H R1 R2 … Rn-2 Rn-1 — — — — — — — — — — — — — — L L R1 R2 … Rn-2 Rn-1 — — — — — — — — — — — — — — — — — — — X — R0 R1 R2 … Rn-1 Rn — — — — — — — — — — X X X … X H R0 R1 R2 — Rn-1 Rn — — — — — — — — — P1 P2 P3 L P0 P1 P2 … Pn-1 Pn L P0 P1 P2 — — — — — … Pn-1 Pn — — — — X X X … H X X X … Pn-1 Pn Hi-Z Hi-Z Hi-Z … Hi-Z Hi-Z L = Low-logic level. H = High-logic level. X = Don’t care. P = Present state. R = Previous state. Hi-Z = High impedance. 8 _______________________________________________________________________________________ 16-Port, 36V Constant-Current LED Driver Selecting External Component RSET to Set LED Output Current The MAX6971 uses an external resistor, RSET, to set the LED current for outputs OUT0–OUT15. The minimum allowed value of RSET is 327.3Ω, which sets the output currents to 55mA. The maximum allowed value of RSET is 5kΩ. The reference value, 360Ω, sets the output currents to 50mA. To set a different output current, use the formula: RSET = 18,000 / IOUT where IOUT is the desired output current in mA. Computing Power Dissipation The upper limit for power dissipation (P D ) for the MAX6971 is determined by the following equation: PD = (V+ x I+) + (VOUT x DUTY x IOUT x N) where: V+ = supply voltage I+ = operating supply current when sinking IOUT LED drive current into N outputs DUTY = PWM duty cycle applied to OE N = number of MAX6971 outputs driving LEDs at the same time (maximum is 16) VOUT = MAX6971 port output voltage when driving load LED(s) IOUT = LED drive current programmed by RSET Overtemperature Cutoff The MAX6971 contains an internal temperature sensor that turns off all outputs when the die temperature exceeds approximately +165°C. The outputs are enabled again when the die temperature drops below approximately +140°C. Register contents are not affected, so when a driver is overdissipating, the external symptom is the load LEDs cycling between on and off as the driver repeatedly overheats and cools, alternately turning the LEDs off and then back on again. Power-Supply Considerations The MAX6971 operates with a chip supply V+, and one or more LED supplies. Bypass each supply to GND with a 0.1µF capacitor as close to the MAX6971 as possible. This is normally adequate for static LED driving. For multiplex or PWM applications, it is necessary to add an additional bulk electrolytic capacitor of 4.7µF or more to each supply for every 4 to 16 MAX6971s. The necessary capacitance depends on the LED load current, PWM switching frequency, and serial-interface speed. Inadequate V+ decoupling can cause timing problems, and very noisy LED supplies can affect LED current regulation. Chip Information PROCESS: BiCMOS PD = power dissipation, in mW if currents are in mA Dissipation example: IOUT = 20mA, N = 16, DUTY = 1, VOUT = 2V, V+ = 5.25V PD = (5.25V x 25mA) + (2V x 1 x 20mA x 16) = 0.77W Thus, for a 24-pin TSSOP package (TJA = 1 / 0.0122 = +82°C/W from the Absolute Maximum Ratings), the maximum allowed ambient temperature TA is given by: TJ(MAX) = TA + (PD x TJA) = +150°C = TA + (0.77 x 82°C/W) so TA = +86°C. _______________________________________________________________________________________ 9 MAX6971 Applications Information 16-Port, 36V Constant-Current LED Driver MAX6971 Selector Guide NUMBER OF OUTPUTS PART MAX OUTPUT VOLTAGE (V) MAX OUTPUT CURRENT (mA) MAX6968 8 MAX6977 5.5 LED FAULT DETECTION WATCHDOG — — Yes — MAX6978 Yes Yes MAX6970* — — 8 MAX6981* 36 MAX6980* 55 MAX6969 MAX6979 MAX6971 MAX6983 16 5.5 16 36 Yes — Yes Yes — — Yes Yes — — Yes Yes *Future product—contact factory for availability. Typical Application Circuit +28V +5V µC V+ SCLK CLK MOSI DIN MISO DOUT LOAD LATCH ENABLE OE 360Ω SET GND 0V 10 MAX6971 OUT0 OUT1 OUT2 OUT3 OUT4 OUT5 OUT6 OUT7 OUT8 OUT9 OUT10 OUT11 OUT12 OUT13 OUT14 OUT15 0V ______________________________________________________________________________________ 16-Port, 36V Constant-Current LED Driver TSSOP4.40mm.EPS PACKAGE OUTLINE, TSSOP 4.40mm BODY 21-0066 G 1 1 ______________________________________________________________________________________ 11 MAX6971 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) PDIPN.EPS MAX6971 16-Port, 36V Constant-Current LED Driver Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2005 Maxim Integrated Products Heaney Printed USA is a registered trademark of Maxim Integrated Products, Inc.