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general description the max1836/max1837 high-efficiency step-down con - verters provide a preset 3.3v or 5v output voltage from supply voltages as high as 24v. using external feedback resistors, the output voltage can be adjusted from 1.25v to v in . an internal current-limited switching mosfet delivers load currents up to 125ma (max1836) or 250ma (max1837). the unique current-limited control scheme, operating with duty cycles up to 100%, minimizes the dropout volt - age (120mv at 100ma). additionally, this control scheme reduces supply current under light loads to 12a. high switching frequencies allow the use of tiny surface-mount inductors and output capacitors. the max1836/max1837 step-down converters with inter - nal switching mosfets are available in 6-pin sot23 and 3mm x 3mm tdfn packages, making them ideal for low-cost, low-power, space-sensitive applications. for increased output drive capability, use the max1776 step-down converter that uses an internal 24v switch to deliver up to 500ma. for even higher currents, use the max1626/max1627 step-down controllers that drive an external p-channel mosfet to deliver up to 20w. applications 9v battery systems notebook computers distributed power systems backup supplies 4ma to 20ma loop power supplies industrial control supplies handheld devices features 4.5v to 24v input voltage range preset 3.3v or 5v output adjustable output from 1.25v to v in output currents up to 125ma (max1836) or 250ma (max1837) efficiency over 90% 12a quiescent current 3a shutdown current 100% maximum duty cycle for low dropout small 6-pin sot23 and tdfn packages selector guide appears at end of data sheet. 19-1919; rev 3; 7/06 *ep = exposed pad. t = tape and reel. part temp range pin- package top mark max1836 ett33-t -40c to +85c 6 tdfn-ep* ajg max1836ett50-t -40c to +85c 6 tdfn-ep* aje max1836eut33-t -40c to +85c 6 sot23 aany max1836eut50-t -40c to +85c 6 sot23 aanw max1837 ett33-t -40c to +85c 6 tdfn-ep* ajh max1837ett50-t -40c to +85c 6 tdfn-ep* ajf max1837eut33-t -40c to +85c 6 sot23 aanz max1837eut50-t -40c to +85c 6 sot23 aanx max1836max1837 in gnd lx shdn fb out note: high-current paths shown with bold lines. output 3.3v or 5v input4.5v to 24v gnd lx in 1 6 out 5 shdn fb max1836max1837 max1836max1837 sot23 tdfn top view 23 gnd in 1 fb 23 4 lx 6 out 5 shdn 4 max1836/max1837 24v internal switch, 100% duty cycle, step-down converters typical operating circuit pin conigurations ordering information evaluation kit available downloaded from: http:///
in, shdn to gnd...................................................-0.3v to +25v lx to gnd.......................................................-2v to (v in + 0.3v) out, fb to gnd.......................................................-0.3v to +6v continuous power dissipation (t a = +70c) (note 1) 6-pin sot23 (derate 8.7mw/c above +70c)...........696mw 6-pin tdfn (derate 24.4mw/c above +70c).........1951mw operating temperature range..............................-40c to +85c junction temperature.......................................................+150c storage temperature range...............................-65c to +150c lead temperature (soldering, 10s)...................................+300c (circuits of figures 1 (max1836) and 2 (max1837), v in = 12v, shdn = in, t a = 0c to +85c . typical values are at t a = +25c, unless otherwise noted.)dual mode is a trademark of maxim integrated products, inc. parameter symbol conditions min typ max units input supply range v in 4.5 24 v input undervoltage lockout threshold v uvlo v in rising 3.55 4.0 4.4 v v in falling 3.45 3.9 4.3 input supply current i in 12 25 a input supply current in dropout i in(drop) v in = 5v 18 a input shutdown current shdn = gnd 3 7 a output voltage (preset mode) v out fb = gnd, i load = 0 to 125ma (max1836) or 250ma (max1837) max183_eut50, max183_ett50 4.80 5.00 5.20 v max183_eut33, max183_ett33 3.168 3.30 3.432 output voltage range (adjustable mode) v out (note 2) 1.25 v in v feedback set voltage (adjustable mode) v fb 1.200 1.25 1.300 v out bias current v out = 5v 2.5 7.4 a fb bias current i fb v fb = 0 or 1.25v, t a = +25c -25 +25 na fb dual mode tm threshold v fb rising or falling 50 100 150 mv lx switch minimum off-time t off(min) 0.2 0.4 0.6 s lx switch maximum on-time t on(max) v fb = 1.3v 7 10 13 s lx switch on-resistance r lx v in = 6v 1.1 2 ? lx current limit i lim max1836 250 312 450 ma max1837 500 625 850 lx zero-crossing threshold -75 +75 mv max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 2 note 1: thermal properties are specified with product mounted on pc board with 1in 2 of copper area and still air. absolute maximum ratings 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 downloaded from: http:///
(circuits of figures 1 (max1836) and 2 (max1837), v in = 12v, shdn = in, t a = -40c to +85c , unless otherwise noted.) (note 4) (circuits of figures 1 (max1836) and 2 (max1837), v in = 12v, shdn = in, t a = 0c to +85c . typical values are at t a = +25c, unless otherwise noted.) parameter symbol conditions min typ max units zero-crossing timeout lx does not rise above the threshold 30 s lx switch leakage current v in = 18v, lx = gnd, t a = +25c 1 a dropout voltage v dropout i out = 100ma, v in = 5v 120 mv line regulation v in = 5v to 24v 0.05 % load regulation i out = 0 to 125ma (max1836) or 250ma (max1837) 0.3 % shutdown input threshold v shdn v in = 4.5v to 24v (note 3) 0.8 2.4 v shutdown leakage current i shdn v shdn = 0 or 24v -1 +1 a thermal shutdown 10c hysteresis (typ) 160 c parameter symbol conditions min typ max units input supply range v in 4.5 24 v input undervoltage lockout threshold v uvlo v in rising 3.55 4.4 v v in falling 3.45 4.3 input supply current i in 25 a input shutdown current shdn = gnd 7 a output voltage (preset mode) v out fb = gnd, i load = 0 to 125ma (max1836) or 250ma (max1837) max183_eut50, max183_ett50 4.80 5.20 v max183_eut33, max183_ett33 3.168 3.432 output voltage range (adjustable mode) v out (note 2) 1.25 v in v feedback set voltage (adjustable mode) v fb 1.200 1.300 v out bias current v out = 5v 7.4 a fb dual mode threshold v fb rising or falling 50 150 mv lx switch minimum off-time t off(min) 0.2 0.6 s lx switch maximum on-time t on(max) v fb = 1.3v 7 13 s lx switch on-resistance r lx v in = 6v 2 ? lx current limit i lim max1836 250 450 ma max1837 500 900 max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 3 electrical characteristics electrical characteristics (continued) downloaded from: http:///
(circuits of figures 1 (max1836) and 2 (max1837), v in = 12v, shdn = in, t a = -40c to +85c , unless otherwise noted.) (note 4) note 2: when using the shutdown input, the maximum output voltage allowed with external feedback is 5.5v. if the output voltage is set above 5.5v, connect shutdown to the input. note 3: shutdown input minimum slew rate (rising or falling) is 10v/ms. note 4: specifications to -40c are guaranteed by design, not production tested. (circuits of figures 1 (max1836) and 2 (max1837), v in = 12v, shdn = in, t a = +25c.) parameter symbol conditions min typ max units lx zero-crossing threshold -75 +75 mv shutdown input threshold v shdn v in = 4.5v to 24v (note 3) 0.8 2.4 v shutdown leakage current i shdn v shdn = 0 or 24v -1 +1 a 100 9590 85 80 70 0.1 10 100 1 1000 max1836eut33 efficiency vs. load current max1836/7 toc02 load current (ma) efficiency (%) 75 v in = 9v v in = 12v v in = 5v figure 1v out = 3.3v 3.27 3.293.28 3.313.30 3.32 3.33 0 150 200 50 100 250 300 350 max1837eut33 output voltage vs. load current max1836/7 toc03 load current (ma) output voltage (v) v in = 9v v in = 5v v in = 12v figure 2 100 9590 85 80 70 0.1 10 100 1 1000 max1837eut33 efficiency vs. load current max1836/7 toc04 load current (ma) efficiency (%) 75 v in = 9v v in = 12v v in = 5v figure 2v out = 3.3v 0 4020 100 8060 160140 120 180 0 100 150 50 200 250 300 350 max1837eut33 switching frequency vs. load current max1836/7 toc05 load current (ma) frequency (khz) v in = 9v v in = 5v v in = 12v figure 2v out = 3.3v 3.27 3.293.28 3.313.30 3.32 3.33 0 4 8 12 16 20 24 max1837eut33 output voltage vs. input voltage max1836/7 toc06 input voltage (v) output voltage (v) i out = 10ma i out = 200ma figure 2v out = 3.3v l1 = 47h 3.27 3.293.28 3.313.30 3.32 3.33 0 100 50 150 200 max1836eut33 output voltage vs. load current max1836/7 toc01 load current (ma) output voltage (v) v in = 5v v in = 9v to 12v figure 1 max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 4 electrical characteristics (continued) typical operating characteristics downloaded from: http:///
(circuits of figures 1 (max1836) and 2 (max1837), v in = 12v, shdn = in, t a = +25c.) 70 8075 9085 95 100 0 4 8 12 16 20 24 max1837eut33 efficiency vs. input voltage max1836/7 toc07 input voltage (v) efficiency (%) i out = 10ma i out = 200ma figure 2 v out = 3.3v l1 = 47h 100 1 0 8 12 10 input voltage (v) frequency (khz) 4 max1837eut33 switching frequency vs. input voltage 16 24 20 max1836/7 toc08 i out = 200ma i out = 10ma figure 2 v out = 3.3v l1 = 47h 0 200 600400 800 1000 0 4 8 12 16 20 24 max1837eut33 peak inductor current vs. input voltage max1836/7 toc09 input voltage (v) peak inductor current (ma) i out = 10ma i out = 200ma figure 2v out = 3.3v l1 = 47h limited by t on(min) limited by i lim 4.96 4.98 5.00 5.02 5.04 0 100 50 150 200 250 300 max1837eut50 output voltage vs. load current max1836/7 toc10 load current (ma) output voltage (v) v in = 12v to 24v v in = 7v v in = 9v figure 6 100 9590 85 80 70 0.1 10 100 1 1000 max1837eut50 efficiency vs. load current max1836/7 toc11 load current (ma) efficiency (%) 75 v in = 9v v in = 24v v in = 18v v in = 7v figure 6v out = 5v v in = 12v 200 250 300 350 400 0 100 200 300 max1837eut50 dropout voltage vs. load current max1836/7 toc12 load current (ma) dropout voltage (mv) 0 50 100 150 figure 6v out = 5v 10 11 12 13 14 15 0 4 8 12 16 20 24 no-load supply current vs. input voltage max1836/7 toc13 input voltage (v) supply current (a) maxim integrated 5 www.maximintegrated.com max1836/max1837 24v internal switch, 100% duty cycle, step-down converters typical operating characteristics (continued) downloaded from: http:///
(circuits of figures 1 (max1836) and 2 (max1837), v in = 12v, shdn = in, t a = +25c.) 100s/div max1837eut50 load transient a: i out = 10ma to 250ma, 200ma/div b: v out = 5v, 20mv/div c: i l , 500ma/div v in = 12v, figure 6 400ma200ma 5.02v 0 b ac max1836/7 toc14 5.00v4.98v 750ma250ma 0 400s/div max1837eut50 line transient a: v in = 9v to 18v, 10v/div b: v out = 5v, r out = 100 ? , 100mv/div c: i l , 500ma/div figure 6 20v10v 5.1v 0 b ac max1836/7 toc15 5.0v4.9v 500ma 0 400s/div max1837eut50 line transient near dropout a: v in = 5v to 12v, 5v/div b: v out = 5v, r out = 100 ? , 100mv/div c: i l , 500ma/div figure 6 15v10v 5.1v 5v b ac max1836/7 toc16 5.0v4.9v 500ma 0 200s/div max1837eut50 startup waveform a: v shdn = 0 to 2v, 2v/div b: v out = 5v, r out = 100 ? , 2v/div c: i l , 500ma/div v in = 12v, figure 6 2v 0 2v 4v b ac max1836/7 toc17 0 500ma 0 max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 6 typical operating characteristics (continued) downloaded from: http:///
detailed description the max1836/max1837 step-down converters are designed primarily for battery-powered devices, notebook computers, and industrial control applications. a unique current-limited control scheme provides high efficiency over a wide load range. operation up to 100% duty cycle allows the lowest possible dropout voltage, increasing the useable supply voltage range. under no-load, the max1836/max1837 draw only 12a, and in shutdown mode, they draw only 3a to further reduce power con - sumption and extend battery life. additionally, an internal 24v switching mosfet, internal current sensing, and a high switching frequency minimize pc board space and component cost. current-limited control architecture the max1836/max1837 use a proprietary current-limited control scheme that operates with duty cycles up to 100%. these dc-dc converters pulse as needed to maintain regulation, resulting in a variable switching frequency that increases with the load. this eliminates the high supply currents associated with conventional constant-frequency pulse-width-modulation (pwm) controllers that switch the mosfet unnecessarily. figure 1. typical max1836 application circuit figure 2. typical max1837 application circuit pin name function 1 fb dual-mode feedback input. connect to gnd for the preset 3.3v (max183_eut33) or 5.0v (max183_eut50) output. connect to a resistive divider between the output and fb to adjust the output voltage between 1.25v and v in , and connect the out pin to gnd. when setting output voltages above 5.5v, permanently connect shdn to in. 2 gnd ground 3 in input voltage. 4.5v to 24v input range. connected to the internal p-channel power mosfets source. 4 lx inductor connection. connected to the internal p-channel power mosfets drain. 5 shdn shutdown input. a logic-low shuts down the max1836/max1837 and reduces supply current to 3a. lx is high impedance in shutdown. connect to in for normal operation. when setting output voltages above 5.5v, permanently connect shdn to in. 6 out regulated output voltage high-impedance sense input. internally connected to a resistive divider. co nnect to the output when using the preset output voltage. connect to gnd when using an external resistive divider to adjust the output voltage. ep exposed metal pad. connect to gnd. this pad is internally connected to gnd through a soft connect. for proper grounding and good thermal dissipation. connect the exposed pad to gnd. max1836 in gnd lx fb out output 3.3v or 5v input4.5v or 12v c in 10f 25v d1 l1 47h c out 100f6.3v c in = taiyo yuden tmk432bj106km l1 = sumida cdrh5d28-470c out = sanyo poscap 6tpc100m (smaller capacitors can be used for 5v) d1 = nihon ep05q03lnote : high-current paths shown with bold lines. shdn max1837 in gnd lx shdn fb out output 3.3v or 5v input4.5v or 12v c in 10f 25v d1 l1 22h c out 150f6.3v c in = taiyo yuden tmk432bj106km l1 = sumida cdrh5d28-220c out = sanyo os-con 6sa150m (smaller capacitors can be used for 5v) d1 = nihon ed05q03lnote: high-current paths shown with bold lines. max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 7 pin description downloaded from: http:///
when the output voltage is too low, an error compara - tor sets a flip-flop, which turns on the internal p-channel mosfet and begins a switching cycle ( figure 3 ). as shown in figure 4 , the inductor current ramps up linearly, charging the output capacitor and servicing the load. the mosfet turns off when the current limit is reached, or when the maximum on-time is exceeded while the output voltage is in regulation. otherwise, the mosfet remains on, allowing a duty cycle up to 100% to ensure the lowest possible dropout voltage. once the mosfet turns off, the flip-flop resets, diode d1 turns on, and the current through the inductor ramps back down, transferring the stored energy to the output capacitor and load. the mosfet remains off until the 0.5s minimum off-time expires and the inductor current ramps down to zero, and the output voltage drops back below the set point. figure 3. functional diagram figure 4. discontinuous-conduction operation input4.5v or 24v c in output 3.3v or 5v d1 l1 c out max1836max1837 in gnd lx shdn fb out q maximum on-time delay trig q maximum off-time delay trig q r s v sense v set 1.25v 100mv 4s/div circuit of figure 2, v in = 12v a. v lx , 5v/div b. v out = 3.3v, 20mv/div, 200ma load c. inductor current, 500ma/div 10v 0 500ma 3.3v ab c 0 max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 8 downloaded from: http:///
input-output (dropout) voltage a step-down converters minimum input-to-output volt - age differential (dropout voltage) determines the lowest useable input supply voltage. in battery-powered sys - tems, this limits the useful end-of-life battery voltage. to maximize battery life, the max1836/max1837 operate with duty cycles up to 100%, which minimizes the input- to-output voltage differential. when the supply voltage approaches the output voltage, the p-channel mosfet remains on continuously to supply the load. dropout voltage is defined as the difference between the input and output voltages when the input is low enough for the output to drop out of regulation. for a step-down con - verter with 100% duty cycle, the dropout voltage depends on the mosfet drain-to-source on-resistance (r ds(on) ) and inductor series resistance; therefore, it is proportional to the load current: ( ) dropout out ds(on) inductor v ir r = + shutdown ( shdn ) a logic-level low voltage on shdn shuts down the max1836/max1837. when shut down, the supply cur - rent drops to 3a to maximize battery life, and the internal p-channel mosfet turns off to isolate the output from the input. the output capacitance and load current determine the rate at which the output voltage decays. a logic-level high voltage on shdn activates the max1836/max1837. do not leave shdn floating. if unused, connect shdn to in. when setting output voltages above 5.5v, the shut - down feature cannot be used, so shdn must be perma - nently connected to in. the shdn input voltage slew rate must be greater than 10v/ms.thermal-overload protection thermal-overload protection limits total power dissipa - tion in the max1836/max1837. when the junction tem - perature exceeds t j = +160c, a thermal sensor turns off the pass transistor, allowing the ic to cool. the thermal sensor turns the pass transistor on again after the ics junction temperature cools by 10c, resulting in a pulsed output during continuous thermal-overload conditions. design information output voltage selection the feedback input features dual-mode operation. connect the output to out and fb to gnd for the preset output voltage. the max1836/max1837 are supplied with factory-set output voltages of 3.3v or 5v. the two- digit part number suffix identifies the output voltage. see the selector guide . for example, the max1836eut33 has a preset 3.3v output voltage. the max1836/max1837 output voltage may be adjusted by connecting a voltage divider from the output to fb ( figure 5 ). when externally adjusting the output voltage, connect out to gnd. select r2 in the 10k to 100k range. calculate r1 with the following equation: out fb v r1 r2 1 v ?? ?? = ? ?? ?? ?? ?? ?? where v fb = 1.25v, and v out may range from 1.25v to v in . when setting output voltages above 5.5v, the shut - down feature cannot be used, so shdn must be perma - nently connected to in.inductor selection when selecting the inductor, consider these four param - eters: inductance value, saturation current rating, series resistance, and size. the max1836/max1837 operate with a wide range of inductance values. for most applica - tions, values between 10h and 100h work best with the controllers switching frequency. calculate the mini - mum inductance value as follows: ( ) in(max) out on(min) (min) lim v vt l i ? = where t on(min) = 1.0s. inductor values up to six times l (min) are acceptable. low-value inductors may be small - er in physical size and less expensive, but they result in higher peak-current overshoot due to current-sense com - parator propagation delay (300ns). peak-current over - shoot reduces efficiency and could exceed the current ratings of the internal switching mosfet and external components. figure 5. adjustable output voltage max1836max1837 in gnd lx shdn fb out note: high-current paths shown with bold lines. output 1.25v to v in input4.5v or 24v c in d1 l1 c out r1 r2 max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 9 downloaded from: http:///
the inductors saturation current rating must be greater than the peak switching current, which is determined by the switch current limit plus the overshoot due to the 300ns current-sense comparator propagation delay: ( ) in out peak lim v v 300ns ii l ? = + where the switch current-limit (i lim ) is typically 312ma (max1836) or 625ma (max1837). saturation occurs when the inductors magnetic flux density reaches the maximum level the core can support, and the inductance starts to fall. inductor series resistance affects both efficiency and dropout voltage. see the input-output (dropout) voltage section. high series resistance limits the maximum current available at lower input voltages and increases the drop - out voltage. for optimum performance, select an inductor with the lowest possible dc resistance that fits in the allotted dimensions. typically, the inductors series resis - tance should be significantly less than that of the internal p-channel mosfets on-resistance (1.1 typ). inductors with a ferrite core, or equivalent, are recommended. the maximum output current of the max1836/max1837 current-limited converter is limited by the peak inductor current. for the typical application, the maximum output current is approximately: out(max) peak ii output capacitor choose the output capacitor to supply the maximum load current with acceptable voltage ripple. the output ripple has two components: variations in the charge stored in the output capacitor with each lx pulse, and the voltage drop across the capacitors equivalent series resistance (esr) caused by the current into and out of the capacitor: ripple ripple(esr) ripple(c) vv v + the output voltage ripple as a consequence of the esr and output capacitance is: ( ) ripple(esr) peak 2 peak out in ripple(c) out out in out v i esr li i v v 2c v v v = ?? ? = ?? ? ?? where i peak is the peak inductor current. see the inductor selection section. these equations are suitable for initial capacitor selection, but final values should be set by test - ing a prototype or evaluation circuit. as a general rule, a smaller amount of charge delivered in each pulse results in less output ripple. since the amount of charge deliv - ered in each oscillator pulse is determined by the inductor value and input voltage, the voltage ripple increases with larger inductance but decreases with lower input voltages. with low-cost aluminum electrolytic capacitors, the esr- induced ripple can be larger than that caused by the current into and out of the capacitor. consequently, high- quality low-esr aluminum-electrolytic, tantalum, polymer, or ceramic filter capacitors are required to minimize out - put ripple. best results at reasonable cost are typically achieved with an aluminum-electrolytic capacitor in the 100f range, in parallel with a 0.1f ceramic capacitor. input capacitor the input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on the input caused by the circuits switching. the input capacitor must meet the ripple-current requirement (i rms ) imposed by the switching currents defined by the following equation: ( ) out in out rms load in v vv ii v ? = for most applications, nontantalum chemistries (ceramic, aluminum, polymer, or os-con) are preferred due to their robustness with high inrush currents typical of sys - tems with low-impedance battery inputs. alternatively, two (or more) smaller-value low-esr capacitors can be connected in parallel for lower cost. choose an input capacitor that exhibits < +10c temperature rise at the rms input current for optimal circuit longevity. diode selection the current in the external diode (d1) changes abruptly from zero to its peak value each time the lx switch turns off. to avoid excessive losses, the diode must have a fast turn-on time and a low forward voltage. use a diode with an rms current rating of 0.5a or greater, and with a breakdown voltage > v in . schottky diodes are preferred. for high-temperature applications, schottky diodes may be inadequate due to their high leakage currents. in such cases, ultra-high-speed silicon rectifiers are recom - mended, although a schottky diode with a higher reverse voltage rating can often provide acceptable performance. max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 10 downloaded from: http:///
max1836/max1837 stability commonly, instability is caused by excessive noise on the feedback signal or ground due to poor layout or improper component selection. when seen, instability typically manifests itself as motorboating, which is characterized by grouped switching pulses with large gaps and exces - sive low-frequency output ripple during no-load or light- load conditions. pc board layout and grounding high switching frequencies and large peak currents make pc board layout an important part of the design. poor lay - out may introduce switching noise into the feedback path, resulting in jitter, instability, or degraded performance. high-power traces, bolded in the typical application cir - cuits ( figure 1 and figure 2 ), should be as short and wide as possible. additionally, the current loops formed by the power components (c in , c out , l1, and d1) should be as tight as possible to avoid radiated noise. connect the ground pins of these power components at a common node in a star-ground configuration. separate the noisy traces, such as the lx node, from the feedback network with grounded copper. furthermore, keep the extra cop - per on the board, and integrate it into a pseudoground plane. when using external feedback, place the resistors as close to the feedback pin as possible to minimize noise coupling. the max1837 evaluation kit shows the recom - mended layout. applications information high-voltage step-down converter the typical application circuits ( figure 1 and figure 2 ) components were selected for 9v battery applications. however, the max1836/max1837 input voltage range allows supply voltages up to 24v. figure 6 shows a modi - fied application circuit for high-voltage applications. when using higher input voltages, verify that the input capaci - tors voltage rating exceeds v in(max) and that the induc - tor value exceeds the minimum inductance recommended in the inductor selection section. inverter coniguration figure 7 shows the max1836/max1837 in a floating ground configuration. by connecting what would nor - mally be the output to the supply-voltage ground, the ics ground pin is forced to regulate to -5v (max183_eut50) or -3.3v (max183_eut33). avoid exceeding the maxi - mum ratings of 24v between in and gnd, and 5.5v between out and gnd. other negative voltages may be generated by placing a resistive divider across the output capacitor and connecting the tap to fb in the same man - ner as the normal step-down configuration. table 1. component suppliers supplier phone fax website inductors coilcraft 847-639-6400 847-639-1469 www.coilcraft.com coiltronics 561-241-7876 561-241-9339 www.coiltronics.com sumida usa 847-956-0666 847-956-0702 www.sumida.com toko 847-297-0070 847-699-1194 www.tokoam.com capacitors avx 803-946-0690 803-626-3123 www.avxcorp.com kemet 408-986-0424 408-986-1442 www.kemet.com panasonic 847-468-5624 847-468-5815 www.panasonic.com sanyo 619-661-6835 619-661-1055 www.secc.co.jp taiyo yuden 408-573-4150 408-573-4159 www.t-yuden.com diodes central semiconductor 516-435-1110 516-435-1824 www.centralsemi.com international rectiier 310-322-3331 310-322-3332 www.irf.com nihon 847-843-7500 847-843-2798 www.niec.co.jp on semiconductor 602-303-5454 602-994-6430 www.onsemi.com zetex 516-543-7100 516-864-7630 www.zetex.com max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 11 downloaded from: http:///
figure 6. high-voltage application figure 7. max1836/max1837 inverter configuration part preset output voltage (v) load current (ma) max1836 ett33 3.3 125 max1836ett50 5 125 max1836eut33 3.3 125 max1836eut50 5 125 max1837 ett33 3.3 250 max1837ett50 5 250 max1837eut33 3.3 250 max1837eut50 5 250 max1837 in gnd lx shdn fb out output 5v input4.5v to 24v c in 10f 25v d1 l1 47h c out 68f10v c in = taiyo yuden tmk432bj106km l1 = sumida cdrh5d28-470c out = sanyo poscap 10tpc68m d1 = nihon ep05q03lnote: high-current paths shown with bold lines. max1836max1837 in gnd lx shdn fb out input3.6v to 18v c in 10f d1 l1 47h c out 100f note: high-current paths shown with bold lines. output -3.3v or -5v max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 12 chip information transistor count: 731 process: bicmos selector guide downloaded from: http:///
max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 13 package information for the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different su ffix character, but the drawing pertains to the package regardless of rohs status. downloaded from: http:///
max1836/max1837 24v internal switch, 100% duty cycle, step-down converters www.maximintegrated.com maxim integrated 14 package information (continued) for the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different su ffix character, but the drawing pertains to the package regardless of rohs status. downloaded from: http:///
maxim integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim integrated product. no circuit patent licenses are implied. maxim integrated reserves the right to change the circuitry and speciications without n otice at any time. the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. maxim integrated and the maxim integrated logo are trademarks of maxim integrated products, inc. ? 2006 maxim integrated products, inc. 15 max1836/max1837 24v internal switch, 100% duty cycle, step-down converters revision history pages changed at rev 3: 1, 7, 8, 12 package information (continued) for the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different su ffix character, but the drawing pertains to the package regardless of rohs status. for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim integrateds website at www.maximintegrated.com. downloaded from: http:///

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