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general description 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-cur- rent 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-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 dout output 16 clock cycles later to allow cascading of multi- ple 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 output- enable, 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-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? to +125? temperature range. 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 ? -40c to +125c temperature range max6971 16-port, 36v constant-current led driver ________________________________________________________________ maxim integrated products 1 24 23 22 21 20 19 18 17 1 2 3 4 5 6 7 8 v+ set dout oe le clk din gnd top view out15 out14 out13 out12 out3 out2 out1 out0 16 15 14 13 9 10 11 12 out11 out10 out9 out8 out7 out6 out5 out4 tssop/pdip max6971aug max6971ang pin configuration ordering information 19-3808; rev 1; 10/07 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. typical application circuit and selector guide appear at end of data sheet. evaluation kit available applications variable message signs marquee displays point-of-order signs traffic signs gaming features architectural lighting part temp range pin-package max6971aug -40? to +125? 24 tssop max6971ang -40? to +125? 24 narrow pdip
max6971 16-port, 36v constant-current led driver 2 _______________________________________________________________________________________ absolute maximum ratings stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. 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 ..................................................................?0ma out_ sink current .............................................................60ma total gnd current ...........................................................960ma continuous power dissipation (t a = +70?) 24-pin tssop (derate 12.2mw/? over +70?) ..........975mw 24-pin pdip (derate 13.3mw/? over +70?)............1067mw operating temperature range .........................-40? to +125? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? electrical characteristics ( typical operating circuit , v+ = 3v to 5.5v, t a = t min to t max , unless otherwise noted. typical values are at v+ = 5v, t a = +25?.) (note 1) parameter symbol conditions min typ max units operating supply voltage v+ 3.0 5.5 v output voltage v out 36 v standby current (interface idle, all output ports high impedance, r set = 360 ) i + all logic inputs at v+ or gnd, dout unloaded 5.7 8 ma standby current (interface running, all output ports high impedance, r set = 360 ) i + f clk = 5mhz, oe = v+, din and le = v+ or gnd, dout unloaded 6 8.5 ma supply current (interface idle, all output ports active low, r set = 360 ) i + all logic inputs at v+ or gnd, dout unloaded 18 25 ma input high voltage din, clk, le, oe v ih 0.7 x v+ v input low voltage din, clk, le, oe v il 0.3 x v+ v hysteresis voltage din, clk, le, oe v i 0.8 v input leakage current din, clk, le, oe i ih , i il -1 +1 ? output high-voltage dout v oh i source = 4ma v + - 0.5v v output low voltage v ol i sink = 4ma 0.5 v output current out_ i out v+ = 3v to 5.5v, v out = 0.8v to 2.5v, r set = 360 37 50 61 ma output leakage current out_ i leak oe = v+ 1 a note 1: all parameters tested at t a = +25?. specifications over temperature are guaranteed by design.
max6971 16-port, 36v constant-current led driver _______________________________________________________________________________________ 3 5v timing characteristics ( typical operating circuit , v+ = 4.5v to 5.5v, t a = t min to t max , unless otherwise noted.) (notes 1, 2, 3) parameter symbol conditions min typ max units clk clock period t cp 40 ns clk pulse-width high t ch 19 ns clk pulse-width low t cl 19 ns din setup time t ds 4ns din hold time t dh 8ns dout propagation delay t do 12 32 ns dout rise and fall time t dr , t df c dout = 10pf, 20% to 80% 10 ns le pulse-width high t lw 20 ns le setup time t ls 10 ns le rising to out_ rising delay t lrr (note 3) 100 ns le rising to out_ falling delay t lrf (note 3) 300 ns clk rising to out_ rising delay t crr (note 3) 100 ns clk rising to out_ falling delay t crf (note 3) 310 ns oe rising to out_ rising delay t oe h (note 3) 100 ns oe falling to out_ falling delay t oe l (note 3) 320 ns led output out_ turn-on fall time t f 80% to 20%, pullup resistor = 65 120 ns led output out_ turn-off rise time t r 20% to 80%, pullup resistor = 65 120 ns note 1: all parameters tested at t a = +25?. specifications over temperature are guaranteed by design. note 2: see figure 3. note 3: a 65 pullup resistor connected from out_ to 5.5v.
max6971 16-port, 36v constant-current led driver 4 _______________________________________________________________________________________ typical operating characteristics (t a = +25?, unless otherwise noted.) 3.3v timing characteristics ( typical operating circuit , v+ = 3v to 5.5v, t a = t min to t max , unless otherwise noted.) (notes 1, 2) parameter symbol conditions min typ max units clk clock period t cp 52 ns clk pulse-width high t ch 24 ns clk pulse-width low t cl 24 ns din setup time t ds 4ns din hold time t dh 8ns dout propagation delay t do 12 50 ns dout rise and fall time t dr , t df c dout = 10pf, 20% to 80% 12 ns le pulse-width high t lw 20 ns le setup time t ls 15 ns le rising to out_ rising delay t lrr (note 3) 120 ns le rising to out_ falling delay t lrf (note 3) 310 ns clk rising to out_ rising delay t crr (note 3) 120 ns clk rising to out_ falling delay t crf (note 3) 330 ns oe rising to out_ rising delay t oe h (note 3) 120 ns oe falling to out_ falling delay t oe l (note 3) 330 ns led output out_ turn-on fall time t f 80% to 20% (note 3) 120 ns led output out_ turn-off rise time t r 20% to 80% (note 3) 120 ns note 1: all parameters tested at t a = +25?. specifications over temperature are guaranteed by design. note 2: see figure 3. note 3: a 65 pullup resistor connected from out_ to 5.5v. supply current vs. supply voltage (interface idle, all outputs off, r set = 720 ) max6971 toc01 supply voltage (v) supply current (ma) 5.0 4.5 3.5 4.0 1.85 1.90 1.95 2.00 1.80 3.0 5.5 t a = +125 c t a = +85 c t a = -40 c t a = +25 c supply current vs. supply voltage (interface idle, all outputs off, r set = 360 ) max6971 toc02 supply voltage (v) supply current (ma) 5.0 4.5 3.5 4.0 3.55 3.60 3.65 3.70 3.50 3.0 5.5 t a = +125 c t a = +85 c t a = -40 c t a = +25 c 10 30 25 20 15 35 40 3.0 4.0 3.5 4.5 5.0 5.5 max6971 toc03 supply voltage (v) supply current (ma) supply current vs. supply voltage (interface idle, all outputs on, r set = 720 ) t a = +125 c t a = +85 c t a = +25 c t a = -40 c
max6971 16-port, 36v constant-current led driver _______________________________________________________________________________________ 5 typical operating characteristics (continued) (t a = +25?, unless otherwise noted.) 15 20 30 25 45 40 35 3.0 4.0 3.5 4.5 5.0 5.5 max6971 toc04 supply voltage (v) supply current (ma) supply current vs. supply voltage (interface idle, all outputs on, r set = 360 ) t a = +125 c t a = +85 c t a = +25 c t a = -40 c 0 10 5 20 15 25 30 0 1.0 1.5 0.5 2.0 2.5 3.0 port output current vs. port output voltage (r set = 720 , v+ = 3.3v) max6971 toc05 port output voltage (v) port output current (ma) t a = +125 c t a = +85 c t a = +25 c t a = -40 c 0 20 10 40 30 50 60 0 1.0 1.5 0.5 2.0 2.5 3.0 port output current vs. port output voltage (r set = 360 , v+ = 3.3v) max6971 toc06 port output voltage (v) port output current (ma) t a = +125 c t a = +85 c t a = -40 c t a = +25 c 0 10 5 20 15 25 30 0 1.0 1.5 0.5 2.0 2.5 3.0 port output current vs. port output voltage (r set = 720 , v+ = 5.0v) max6971 toc07 port output voltage (v) port output current (ma) t a = +125 c t a = +85 c t a = +25 c t a = -40 c 0 20 10 40 30 50 60 0 1.0 1.5 0.5 2.0 2.5 3.0 port output current vs. port output voltage (r set = 360 , v+ = 5.0v) max6971 toc08 port output voltage (v) port output current (ma) t a = +125 c t a = +85 c t a = +25 c t a = -40 c 25.0 24.5 24.0 23.5 23.0 3.0 4.0 3.5 4.5 5.0 5.5 port output current vs. supply voltage (r set = 720 , v out = 2v) max6971 toc09 supply voltage (v) port output current (ma) t a = +25 c t a = -40 c t a = +85 c t a = +125 c 49 48 47 46 3.0 4.0 3.5 4.5 5.0 5.5 port output current vs. supply voltage (r set = 360 , v out = 2v) max6971 toc10 supply voltage (v) port output current (ma) t a = +125 c t a = +85 c t a = +25 c t a = -40 c 0 10 30 20 40 50 02 1345 port output current vs. r set resistance (v+ = 5.0v) max6971 toc11 r set resistance (k ) port output current (ma)
max6971 16-port, 36v constant-current led driver 6 _______________________________________________________________________________________ pin description pin name function 1 gnd ground 2 din serial-data input. data is loaded into the internal 16-bit shift register on clk? rising edge. 3 clk serial-clock input. data is loaded into the internal 16-bit shift register on clk? rising edge. 4le load - e nab l e inp ut. d ata i s l oad ed tr ansp ar entl y fr om the i nter nal shi ft r eg i ster ( s) to the outp ut l atch( es) w hi l e le i s hi g h. d ata i s l atched i nto the outp ut l atch( es) on le ? s fal l i ng ed g e, and r etai ned w hi l e le i s l ow . 5?0 out0?ut15 led driver outputs. out0 to out15 are open-drain, constant-current-sinking outputs rated to 36v. 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? rising edge. 23 set led current setting. connect set to gnd through a resistor (r set ) to set the maximum led current. 24 v+ positive supply voltage. bypass v+ to gnd with a 0.1? ceramic capacitor. serial-to-parallel shift register latches out0 out1 out2 dout din clk out15 constant-current sinks out3 out4 power-on reset v+ current reference oe gnd gnd le d0 d15 d0 d15 d0 d15 r set max6971 v+ figure 1. block diagram
detailed description the max6971 led driver comprises a 4-wire serial interface driving 16 constant-current-sinking, open- drain output ports. the outputs drive leds in either static or multiplex applications (figure 1). the constant- current outputs are guaranteed for current accuracy not only with chip-supply voltage variations (5v ?0% and 3v to 5.5v), but also over a realistic range of driver output voltage drop (0.8v to 2.5v). the drivers use cur- rent-sensing feedback circuitry (not simple current mir- rors) 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 reg- ister 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, r set . 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 dis- play data to the max6971. the serial-interface data word length is 16 bits, d0?15. 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. max6971 16-port, 36v constant-current led driver _______________________________________________________________________________________ 7 . d15 d14 t ds t dh t cl t cp t do t oew t oel t f t r t oeh t ls t lw t ch d1 d0 d7 le clk din dout oe out_ 80% 20% t lf figure 2. 4-wire serial-interface timing diagram
max6971 16-port, 36v constant-current led driver 8 _______________________________________________________________________________________ clk is the serial-clock input, which shifts data at din into the max6971 16-bit shift register on its rising edge. 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?ut15 high impedance, without altering the contents of the output latches, and low to enable out- puts out0?ut15 to follow the state of the output latches. oe is independent of the operation of the serial inter- face. 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? 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. le out_ le out_ clk out_ clk out_ t crr t crf t lrr t lrf figure 3. le and clk to out_ timing table 1. 4-wire serial-interface truth table shift-register contents latch contents output contents serial data input din clock input clk d 0 d 1 d 2 ? n-1 d n load input le d 0 d 1 d 2 ? n-1 d n blanking input oe h hr 1 r 2 ? n-2 r n-1 l lr 1 r 2 ? n-2 r n-1 x r 0 r 1 r 2 ? n-1 r n xxxxx h r 0 r 1 r 2 ? n-1 r n p 1 p 2 p 3 ? n-1 p n l p 0 p 1 p 2 ? n-1 p n l p 0 p 1 p 2 p n - 1 p n xxxxx h hi-z hi-z hi-z hi-z hi-z l = low-logic level. h = high-logic level. x = don? care. p = present state. r = previous state. hi-z = high impedance.
applications information selecting external component r set to set led output current the max6971 uses an external resistor, r set , to set the led current for outputs out0?ut15. the minimum allowed value of r set is 327.3 , which sets the output currents to 55ma. the maximum allowed value of r set is 5k . the reference value, 360 , sets the output cur- rents to 50ma. to set a different output current, use the formula: r set = 18,000 / i out where i out 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: p d = (v+ x i+) + (v out x duty x i out x n) where: v+ = supply voltage i+ = operating supply current when sinking i out 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) v out = max6971 port output voltage when driving load led(s) i out = led drive current programmed by r set p d = power dissipation, in mw if currents are in ma dissipation example: i out = 20ma, n = 16, duty = 1, v out = 2v, v+ = 5.25v p d = (5.25v x 25ma) + (2v x 1 x 20ma x 16) = 0.77w thus, for a 24-pin tssop package (t ja = 1 / 0.0122 = +82?/w from the absolute maximum ratings ), the maximum allowed ambient temperature t a is given by: t j(max) = t a + (p d x t ja ) = +150? = t a + (0.77 x 82?/w) so t a = +86?. overtemperature cutoff the max6971 contains an internal temperature sensor that turns off all outputs when the die temperature exceeds approximately +165?. the outputs are enabled again when the die temperature drops below approximately +140?. register contents are not affected, so when a driver is overdissipating, the exter- nal symptom is the load leds cycling between on and off as the driver repeatedly overheats and cools, alter- nately 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 0.1? capacitor as close to the max6971 as pos- sible. this is normally adequate for static led driving. for multiplex or pwm applications, it is necessary to add an additional bulk electrolytic capacitor of 4.7? or more to each supply for every 4 to 16 max6971s. the necessary capacitance depends on the led load cur- rent, 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 max6971 16-port, 36v constant-current led driver _______________________________________________________________________________________ 9
max6971 16-port, 36v constant-current led driver 10 ______________________________________________________________________________________ c mosi out0 out1 out2 out3 out4 out5 out6 out7 sclk din clk 0v gnd miso dout 0v 360 oe enable +5v v+ +28v latch load set max6971 out8 out9 out10 out11 out12 out13 out14 out15 typical application circuit selector guide part number of outputs max output voltage (v) max output current (ma) led fault detection watchdog max6968 max6977 yes max6978 8 5.5 yes yes max6970 max6981 yes max6980 836 yes yes max6969 max6979 16 5.5 yes yes max6971 max6983 16 36 yes yes 55
max6971 16-port, 36v constant-current led driver ______________________________________________________________________________________ 11 tssop4.40mm.eps package outline, tssop 4.40mm body 21-0066 1 1 i package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .)
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 circu it 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 2007 maxim integrated products is a registered trademark of maxim integrated products, inc. heaney package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .) pdipn.eps revision history pages changed at rev 1: 6, 10, 11

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