general description the MAX8595X/max8596x drive up to nine white leds with constant current and high efficiency to provide lcd backlighting in cell phones, pdas, and other handheld devices. the series connection allows the led currents to be identical for uniform brightness and minimizes the number of traces to the leds. the MAX8595X regulates constant led current over the entire temperature range. the max8596x features an ambient-temperature derating function to avoid over- driving the white leds during high ambient tempera- tures, enabling higher drive current below +42?. a single dual mode input provides a simple means of brightness adjustment and on/off control. fast 1mhz current-mode pwm operation allows for small input and output capacitors and a small inductor while minimizing ripple on the input supply/battery. soft-start eliminates inrush current during startup. the MAX8595X/max8596x are available in a space- saving, 8-pin, 3mm x 3mm tdfn package. applications cell phones and smart phones pdas, palmtops, and wireless handhelds e-books and subnotebooks white led display backlighting features ? up to nine leds at 25ma ? temperature derating function to allow fewer leds for same light (max8596x) ? 86% efficiency (p leds / p in ) ? 1.7% current-regulation accuracy ? output overvoltage protection ? flexible dimming control analog direct-pwm internal filter ? 1mhz pwm switching frequency ? 0.1f output capacitor ? 12mv p-p low input ripple ? soft-start eliminates inrush current ? 2.6v to 5.5v input range ? 0.3a shutdown current ? pin compatible with the max1561 and max1599 ? tdfn 3mm x 3mm x 0.8mm package with exposed paddle MAX8595X/max8596x high-efficiency, 36v step-up converters with t a derating option for 2 to 9 white leds ________________________________________________________________ maxim integrated products 1 gnd comp cs 1 2 lx pgnd in ctrl out top view 3 4 MAX8595X max8596x 8 76 5 tdfn 3mm x 3mm x 0.8mm pin configuration ordering information MAX8595X max8596x in lx out pgnd cs ctrl comp gnd 0.1 f 2 to 9 leds 200hz to 200khz analog or pwm dimming 2.2 f input 2.6v to 5.5v output up to 38v typical operating circuit 19-3485; rev 0; 11/04 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available part temp range pin-package pkg code MAX8595X eta -40 c to +85 c 8 tdfn 3mm x 3mm t833-1 max8596x eta* -40 c to +85 c 8 tdfn 3mm x 3mm t833-1 dual mode is a trademark of maxim integrated products, inc. * future product?ontact factory for availability.
MAX8595X/max8596x high-efficiency, 36v step-up converters with t a derating option for 2 to 9 white leds 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. in to gnd .................................................................-0.3v to +6v pgnd to gnd .......................................................-0.3v to +0.3v lx, out to gnd .....................................................-0.3v to +40v ctrl to gnd...................-0.3v to the lower of +6v or (v in + 2v) comp, cs to gnd ......................................-0.3v to (v in + 0.3v) i lx ...................................................................................1.0a rms continuous power dissipation (t a = +70?) 8-pin tdfn 3mm x 3mm (derate 24.4mw/? above +70?) ............................ 1950mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? electrical characteristics (v in = 3.0v, l = 22?, c in = 2.2?, c out = 0.1?, c comp = 0.1?, r sense = 13 ? , v ctrl = 1.5v, t a = -40? to +85?, unless other- wise noted. typical values are at t a = +25?.) (note 1) parameter conditions min typ max units supply voltage 2.6 5.5 v uvlo threshold v in rising or falling 2.10 2.38 2.55 v uvlo hysteresis 30 mv quiescent current no switching 0.5 0.7 ma t a = +25 c 0.3 2 shutdown supply current ctrl = gnd, v out = v in t a = +85 c1 ? ovlo threshold v out rising 36 38 40 v ovlo hysteresis 2v v out = 32v, v ctrl > 0.24v 9 20 35 t a = +25 c 0.01 1 out input bias current out = in, ctrl = gnd t a = +85 c 0.1 ? output voltage range (note 2) v in - v d 36 v error amplifier t a = +25 c 0.295 0.300 0.305 t a = 0 c to +85 c 0.292 0.300 0.308 ctrl to cs regulation v ctrl = 1.50v, v in = 2.6v to 5.5v t a = -40 c to +85 c 0.290 0.300 0.310 v t a = +25 c 0.01 1 cs input bias current v cs = v ctrl / 5 t a = +85 c 0.03 ? MAX8595X, v ctrl = 3.0v 310 330 347 t a = -40 c to +25 c 330 345 360 t a = +42 c 343 cs maximum brightness clamp voltage max8596x, v ctrl = 3.0v t a = +85 c 106.5 mv max8595z 1.65 ctrl voltage for cs maximum brightness clamp max8596z 1.72 v cs derating function start temperature max8596z, v ctrl = 3.0v +42 c
MAX8595X/max8596x high-efficiency, 36v step-up converters with t a derating option for 2 to 9 white leds _______________________________________________________________________________________ 3 electrical characteristics (continued) (v in = 3.0v, l = 22?, c in = 2.2?, c out = 0.1?, c comp = 0.1?, r sense = 13 ? , v ctrl = 1.5v, t a = -40? to +85?, unless other- wise noted. typical values are at t a = +25?.) (note 1) parameter conditions min typ max units cs derating function slope max8596x, v ctrl = 3.0v, t a = +42 c to +85 c -5.5 mv/ c ctrl input resistance v ctrl < 1.5v 250 500 780 k ? ctrl dual-mode threshold 100 170 240 mv ctrl dual-mode hysteresis 5mv ctrl shutdown enable delay (note 3) 6.0 8.2 10.5 ms cs to comp transconductance v comp = 1.5v 32 50 82 ? comp input resistance to ground in shutdown, uvlo or ovlo 20 k ? oscillator operating frequency 0.75 1.0 1.25 mhz pwm mode 12 minimum duty cycle pulse skipping 0 % maximum duty cycle ctrl = in, cs = gnd 94 95 % n-channel switch lx on-resistance i lx = 190ma 0.8 1.35 ? t a = +25 c 0.01 5 lx leakage current v lx = 36v, ctrl = gnd t a = +85 c1 ? lx current limit duty cycle = 90% 500 700 900 ma note 1: parameters are 100% production tested at t a = +25?. limits over the operating temperature range are regulated by design and characterization. note 2: v d is the forward-voltage drop of the schottky diode in figure 1. note 3: time from ctrl going below the dual-mode threshold to ic shutdown.
MAX8595X/max8596x high-efficiency, 36v step-up converters with t a derating option for 2 to 9 white leds 4 _______________________________________________________________________________________ typical operating characteristics (circuit of figure 1, v in = 3.6v, i led = 25ma, l = 22?, c in = 2.2?, c out = 0.1?, c comp = 0.1?, r sense = 13 ? , 4 leds, t a = +25?, unless otherwise noted.) efficiency vs. input voltage MAX8595X toc01 input voltage (v) efficiency (%) 5 4 3 55 60 65 70 75 80 85 90 95 100 50 26 3 leds 4 leds 6 leds 8 leds efficiency vs. led current MAX8595X toc02 led current (ma) efficiency (%) 25 20 15 10 5 65 70 75 80 85 90 60 030 3 leds 6 leds 8 leds led current vs. direct-pwm dimming MAX8595X toc03 duty cycle (%) led current (ma) 80 60 40 20 5 10 15 20 25 30 0 0100 led current vs. ambient temperature MAX8595X toc04 temperature ( c) led current (ma) 80 60 20 40 0 -20 10 12 14 16 18 20 22 24 26 8 -40 100 max8596, i led = 25ma at t a = +25 c max8595, i led = 15ma switching waveforms MAX8595X toc05 500ns/div v in 20mv/div ac-coupled 200mv/div ac-coupled 100ma/div 10v/div v lx v out i l soft-start and shutdown response MAX8595X toc06 20ms/div v ctrl 2v/div 0 0 0 0 40ma/div 10v/div 100ma/div i in i led v out
MAX8595X/max8596x high-efficiency, 36v step-up converters with t a derating option for 2 to 9 white leds _______________________________________________________________________________________ 5 typical operating characteristics (continued) (circuit of figure 1, v in = 3.6v, i led = 25ma, l = 22?, c in = 2.2?, c out = 0.1?, c comp = 0.1?, r sense = 13 ? , 4 leds, t a = +25?, unless otherwise noted.) pin description pin name function 1 out overvoltage sense. when v out is greater than 38v (typ), the internal n-channel mosfet turns off until v out drops below 36v (typ), then the ic reenters soft-start. connect a 0.1? ceramic capacitor from out to ground. in shutdown, v out is one diode drop below v in . 2in input voltage supply. the input voltage range is 2.6v to 5.5v. connect a 2.2? ceramic capacitor from in to gnd. 3 ctrl brightness control input. the voltage applied to ctrl controls led brightness. varying the voltage from 0.24v to 1.65v (1.72v for the max8596x) adjusts the brightness from dim to 100% brightness, respectively. any voltage above 1.65v (1.72v) does not increase brightness. hold ctrl below 100mv to shut down the ic after an 8.2ms delay. 4cs current-sense feedback input. connect a resistor from cs to gnd to set the led bias current. the voltage at cs regulates to v ctrl / 5 or 0.330v (0.343v for the max8596x), whichever is lower. 5 comp compensation input. connect a 0.1? ceramic capacitor (c comp ) from comp to gnd. c comp stabilizes the converter, controls soft-start, and lowpass filters direct pwm dimming at ctrl. c comp discharges to 0v through an internal 20k ? resistor in shutdown. 6 gnd ground. connect to pgnd and the exposed pad directly under the ic. 7 pgnd power ground. connect to gnd and the exposed pad directly under the ic. 8lx inductor connection. connect lx to the node between the inductor and the schottky diode. lx is high impedance in shutdown. ?p exposed pad. connect to a large ground plane for maximum package heat dissipation. connect directly to gnd and pgnd under the ic. direct-pwm dimming response MAX8595X toc08 10 s/div v ctrl 2v/div 32khz 50% duty cycle 0 0 0 0 500mv/div ac-coupled 10ma/div 20mv/div ac-coupled v in v out i led ctrl step response MAX8595X toc07 20ms/div v ctrl 1v/div 0 0 0 0 40ma/div 10v/div 100ma/div i in i led v out
MAX8595X/max8596x detailed description the high efficiency and small size of the MAX8595X/ max8596x make them ideally suited to drive up to nine series-connected leds. these devices operate as a boost dc-dc converter that regulates output current rather than voltage. the MAX8595X/max8596x provide even illumination by sourcing the same output current through each led, eliminating the need for expensive factory calibration. the fast 1mhz internal oscillator allows for a small inductor and small input and output capacitors while minimizing input and output ripple. the single analog control input (ctrl) allows easy adjustment of led brightness and on/off control. this allows simple logic-level on/off control, analog voltage control, or pwm duty-cycle control of both brightness and shutdown. in shutdown, supply current is reduced to a low 0.3? (typ). a soft-start gradually illuminates the leds, eliminating the inrush current during startup. the max8596x has the additional feature of derating led current as ambient temperature rises. above +42 c, the cs regulation voltage is reduced at a rate of 5.5mv/ c, thus reducing the led current. soft-start the MAX8595X/max8596x attain soft-start by charging c comp gradually with a current source. when v comp rises above 1.25v, the internal mosfet begins switch- ing at a reduced duty cycle. when v comp rises above 2.25v, the duty cycle is at its maximum. see the typical operating characteristics for an example of soft-start operation. shutdown the MAX8595X/max8596x enter shutdown when v ctrl is less than 100mv for more than 8.2ms. in shutdown, supply current is reduced to 0.3? (typ) by powering down the entire ic except for the ctrl voltage-detec- tion circuitry. c comp is discharged during shutdown, allowing the device to reinitiate soft-start when it is enabled. although the internal n-channel mosfet does not switch in shutdown, there is still a dc current path between the input and the leds through the inductor and schottky diode. the minimum forward voltage of the led array must exceed the maximum input voltage to ensure that the leds remain off in shutdown. however, with two or more leds, the forward voltage is large enough to keep leakage current low, less than 1? (typ). typical shutdown timing characteristics are shown in the typical operating characteristi cs. overvoltage protection overvoltage lockout (ovlo) occurs when v out is above 38v (typ). the protection circuitry stops the inter- nal mosfet from switching and causes v comp to decay towards 0v. the device comes out of ovlo and into soft-start when v out falls below 36v (typ). ambient temperature derating function (max8596x) the max8596x limits the maximum led current depending on the die temperature. v cs is limited to 343mv up to +42 c. once the temperature reaches +42 c, the maximum v cs declines by 5.5mv/ c until the minimum 106.5mv threshold is reached at +85 c. due to the package? exposed paddle, the die temper- ature is always very close to the pc board temperature. the temperature derating function allows the led cur- rent to be safely set higher at normal operating temper- atures, thereby allowing either a brighter display or fewer leds to be used for normal display brightness. see the typical operating characteristics for led current vs. ambient temperature. high-efficiency, 36v step-up converters with t a derating option for 2 to 9 white leds 6 _______________________________________________________________________________________ 0.1 f pwm control in 2.2 f 22 h lx pgnd over- voltage protect g m cs shutdown 8.2ms gnd comp ctrl 170mv 100k ? 121k ? 279k ? 1.25v clamp or temp derate clamp r sense 13 ? 2.6v to 5.5v f osc 1mhz 0.1 f analog or direct pwm dimming out figure 1. functional diagram and typical application circuit
design procedure adjusting led current adjusting the output current of the MAX8595X/ max8596x changes the brightness of the leds. an analog input (ctrl) and the sense-resistor value set the output current. output current is given by: i led = v ctrl / (5 x r sense ) the v ctrl voltage range for adjusting output current is 0.24v to 1.65v (or 1.72v for the max8596x). to set the maximum current, calculate r sense when v ctrl is at its maximum as follows: for the MAX8595X, r sense = 1.65 / (5 x i led(max) ) for the max8596x, r sense = 1.72 / (5 x i led(max) ) power dissipation in r sense is typically less than 10mw, allowing the use of a small surface-mount resistor. pwm dimming control ctrl is also used as a digital input allowing led brightness control with a logic-level pwm signal applied directly to ctrl. the frequency range is from 200hz to 200khz, while 0% duty cycle corresponds to zero current and 100% duty cycle corresponds to full current. the error amplifier and compensation capaci- tor form a lowpass filter so pwm dimming results in dc current to the leds without the need for any additional rc filters; see the typical operating characteristic s. capacitor selection ceramic capacitors with x5r, x7r, or better dielectric are recommended for stable operation over the entire operating temperature range. the exact values of input and output capacitors are not critical. the typical value for the input capacitor is 2.2?, and the typical value for the output capacitor is 0.1?. higher value capacitors can be used to reduce input and output ripple, but at the expense of size and higher cost. c comp stabilizes the converter and controls soft-start. connect a 0.1? capacitor from comp to gnd. for stable operation, c out must not exceed 10 times c comp . inductor selection inductor values range from 10? to 47?. a 22? inductor optimizes the efficiency for most applications while maintaining low 12mv p-p input ripple. with input voltages near 5v, a larger value of inductance can be more efficient. to prevent core saturation, ensure that the inductor-saturation current rating exceeds the peak inductor current for the application. calculate the peak inductor current with the following formula: schottky diode selection the high switching frequency of the MAX8595X/ max8596x demands a high-speed rectification diode (d1) for optimum efficiency. a schottky diode is recom- mended due to its fast recovery time and low forward- voltage drop. ensure that the diode? average and peak current rating exceed the average output current and peak inductor current. in addition, the diode? reverse breakdown voltage must exceed v out . the rms diode current can be approximated from: applications information pc board layout due to fast switching waveforms and high-current paths, careful pc board layout is required. an evalua- tion kit (max8596xevkit) is available to speed design. when laying out a board, minimize trace lengths between the ic and r sense , the inductor, the diode, the input capacitor, and the output capacitor. keep traces short, direct, and wide. keep noisy traces, such as the lx node trace, away from cs. the in bypass capacitor (c in ) should be placed as close to the ic as possible. pgnd and gnd should be connected direct- ly to the exposed paddle underneath the ic. the ground connections of c in and c out should be as close together as possible. the traces from in to the inductor and from the schottky diode to the leds can be longer. chip information transistor count: 2143 process: bicmos iii diode rms out peak () = i vi v vs l peak out max led max in min in min = + () () () () . . 09 09 2 MAX8595X/max8596x high-efficiency, 36v step-up converters with t a derating option for 2 to 9 white leds _______________________________________________________________________________________ 7
MAX8595X/max8596x high-efficiency, 36v step-up converters with t a derating option for 2 to 9 white leds 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. 8 _____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2004 maxim integrated products printed usa is a registered trademark of maxim integrated products. 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 .) 6, 8, &10l, dfn thin.eps l c l c pin 1 index area d e l e l a e number of leads shown are for reference only e2 detail a n f 1 2 21-0137 package outline, 6, 8, 10 & 14l, tdfn, exposed pad, 3x3x0.80 mm common dimensions symbol min. max. a 0.70 0.80 d 2.90 3.10 e 2.90 3.10 a1 0.00 0.05 l 0.20 0.40 pkg. code n d2 e2 e jedec spec b [(n/2)-1] x e package variations 0.25 min. k a2 0.20 ref. 2.300.10 1.500.10 6 t633-1 0.95 bsc mo229 / weea 1.90 ref f 2 2 21-0137 package outline, 6, 8, 10 & 14l, tdfn, exposed pad, 3x3x0.80 mm 0.400.05 1.95 ref 0.300.05 0.65 bsc 2.300.10 8 t833-1 2.00 ref 0.250.05 0.50 bsc 2.300.10 10 t1033-1 2.40 ref 0.200.03 - - - - 0.40 bsc 1.700.10 2.300.10 14 t1433-1 1.500.10 1.500.10 mo229 / weec mo229 / weed-3 0.40 bsc - - - - 0.200.03 2.40 ref t1433-2 14 2.300.10 1.700.10
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