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????????????????????????????????????????????????????????????????? maxim integrated products 1 19-6245; rev 0; 5/12 ordering information appears at end of data sheet. for related parts and recommended products to use with this part, refer to www.maxim-ic.com/MAX17502.related typical operating circuit general description the max1750 2 high-efficiency, high-voltage, synchro - nous step-down dc-dc converter operates over a 4.5v to 60v input voltage range and is designed for a wide range of applications. the ultra-wide-input operation makes it ideal for not only industrial control and build - ing automation, but also base stations, telecom, home entertainment, and automotive applications. it delivers output currents up to 1a, at output voltages of 3.3v and 5v. the output voltage is accurate within q 1.6% over temperature. the device operates over the -40 n c to +125 n c industrial temperature range and is available in a tiny, 10-pin (3mm x 2mm) tdfn lead(pb)-free package with an exposed pad. the device features peak-current-mode control with pulse-width modulation (pwm). the pwm operation ensures constant switching frequency at all operat - ing conditions. the low-resistance, on-chip, pmos/ nmos switches ensure high efficiency at full load while minimizing the critical inductances, making the layout a much simpler task compared to discrete solutions. the device offers fixed switching frequency of 600khz. to reduce input inrush current, the device offers an adjustable voltage soft-start feature with an external capacitor from the ss pin to ground. the device also incorporates an output enable/undervoltage lockout pin (en/uvlo) that allows the user to turn on the part at the desired input-voltage level. an open-drain reset pin provides a delayed power-good signal to the sys - tem upon achieving successful regulation of the output voltage. the device supports hiccup-mode current-limit protection for low power dissipation under overload and outpu t short-circuit conditions. applications industrial process control hvac and building control general-purpose point-of-load base station, voip, telecom home theater automotive battery-powered equipment benefits and features s eliminate external components and reduce total cost ? no schottky-synchronous operation for high efficiency and reduced cost ? internal compensation for ultra-compact layout ? all-ceramic capacitors s reduce number of dc-dc regulators to stock ? wide 4.5v to 60v operating-voltage range ? fixed 3.3v and 5v output ? delivers up to 1a over temperature ? 600khz switching frequency s reduce power dissipation ? peak efficiency > 90% ? shutdown current = 1 a (typ) s operate reliably in adverse industrial environments ? hiccup-mode current limit and autoretry startup ? built-in output-voltage monitoring (open-drain reset pin) ? resistor-programmable uvlo threshold ? increased safety with adjustable soft-start and prebiased power-up ? optional adjustable output and pfm (available upon factory request) ? -40 n c to +125 n c industrial temperature range c2 1f c3 3300pf n.c. ss v cc en / uvlo v in lx pgnd gnd fb /v o reset v in 24v 20% c1 2.2f 1210 1 2 ju1 r1 3.32mi r2 866ki 3 MAX17502f reset l1 22h c4 10f, 10v 1210 v out 5v, 1a MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxims website at www.maxim-ic.com.
????????????????????????????????????????????????????????????????? maxim integrated products 2 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter v in to gnd ............................................................ -0.3v to +70v en/uvlo to gnd ......................................... -0.3v to v in + 0.3v lx to pgnd ........................................................... -0.3v to +70v fb, reset , comp, ss to gnd ................................. -0.3v to 6v v cc to gnd ............................................................. -0.3v to +6v gnd to pgnd ...................................................... -0.3v to +0.3v lx total rms current ........................................................ q 1.6a output short-circuit duration .................................... continuous continuous power dissipation (t a = +70 n c) 10-pin tdfn (derate 14.9mw/ n c above +70 n c) (multilayer board) ................................................... 1188.7mw operating temperature range ........................ -40 n c to +125 n c junction temperature ..................................................... +150 n c storage temperature range ............................ -65 n c to +160 n c lead temperature (soldering, 10s) ................................ +300 n c soldering temperature (reflow) ...................................... +260 n c absolute maximum ratings note 1: package thermal resistances were obtained using the method described in jedec specification jesd51-7, using a four- layer board. for detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial . stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional opera - tion 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. thermal resistance tdfn junction-to-ambient thermal resistance ( b ja ) ....... 67.3 n c/w junction-to-case thermal resistance ( b jc ) ............ 18.2 n c/w package thermal characteristics (note 1) electrical characteristics (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2 f f, c vcc = 1 f f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected. t a = t j = -40 n c to +125 n c, unless otherwise noted. typical values are at t a = +25 n c. all voltages are referenced to gnd, unless otherwise noted.) (note 2) parameter symbol conditions min typ max units input supply (v in ) input voltage range v in 4.5 60 v input supply current i in-sh v en = 0v, shutdown mode 0.9 3.5 f a i in-sw normal switching mode, v comp = 0.8v v in = 12v 3.7 5.2 ma v in = 24v 5 6.75 enable/uvlo (en/uvlo) en threshold v enr v en rising 1.194 1.218 1.236 v v enf v en falling 1.114 1.135 1.156 v en-truesd v en falling, true shutdown 0.75 en input leakage current i en v en = v in = 60v, t a = +25 n c 7 200 na ldo v cc output voltage range v cc 6v < v in < 12v, 0ma < i vcc < 10ma, 12v < v in < 60v, 0ma < i vcc < 2ma 4.65 5 5.35 v v cc current limit i vcc-max v cc = 4.3v, v in = 12v 17 40 80 ma v cc dropout v cc-do v in = 4.5v, i vcc = 5ma 4.1 v v cc uvlo v cc-uvr v cc rising 3.85 4 4.15 v v cc-uvf v cc falling 3.55 3.7 3.85
????????????????????????????????????????????????????????????????? maxim integrated products 3 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter electrical characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2 f f, c vcc = 1 f f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected. t a = t j = -40 n c to +125 n c, unless otherwise noted. typical values are at t a = +25 n c. all voltages are referenced to gnd, unless otherwise noted.) (note 2) parameter symbol conditions min typ max units lx lx leakage current i lx_lkg v en = 0v, t a = +25 n c, v lx = (v pgnd + 1v) to (v in - 1v) 1 f a soft-start (ss) switchover to internal reference voltage threshold v ss-th 863 880 898 mv charging current i ss v ss = 0.5v 4.7 5 5.3 f a feedback (fb) fb input bias current i fb t a = +25 n c MAX17502e, v fb = 3.3v 6.8 12 17 f a MAX17502f, v fb = 5v 6.8 12 17 f a output voltage (v out ) output voltage range v out MAX17502e only 3.248 3.3 3.352 v MAX17502f only 4.922 5 5.08 current limit peak-current-limit threshold i peak-limit 1.35 1.6 1.85 a runaway-current-limit threshold i runaway- limit 1.55 1.8 2.05 a valley current-limit threshold i sink-limit 0.56 0.65 0.74 a timing switching frequency f sw v fb > v out-hicf MAX17502e/f 560 600 640 khz v fb < v out-hicf 280 300 320 events to hiccup after crossing runaway current limit 1
????????????????????????????????????????????????????????????????? maxim integrated products 4 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter electrical characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2 f f, c vcc = 1 f f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected. t a = t j = -40 n c to +125 n c, unless otherwise noted. typical values are at t a = +25 n c. all voltages are referenced to gnd, unless otherwise noted.) (note 2) note 2: all limits are 100% tested at +25 n c. limits over temperature are guaranteed by design. note 3: guaranteed by design, not production tested. parameter symbol conditions min typ max units v out undervoltage trip level to cause hiccup v out-hicf v ss > 0.95v (soft-start is done) 69.14 71.14 73.14 % hiccup timeout 32,768 cycles minimum on-time t on_min 85 120 ns maximum duty cycle d max v fb = 0.98 x v fb-reg MAX17502e/f 92 94 96 % lx dead time 5 ns reset reset output level low i reset = 1ma 0.02 v reset output leakage current high v fb = 1.01 x v out , t a = +25 n c 0.45 f a v out threshold for reset assertion v out-okf v fb falling 90.5 92.5 94.5 % v out threshold for reset deassertion v out-okr v fb rising 93.5 95.5 97.5 % reset deassertion delay after fb reaches 95% regulation 1024 cycles thermal shutdown thermal-shutdown threshold temperature rising 165 n c thermal-shutdown hysteresis 10 n c
????????????????????????????????????????????????????????????????? maxim integrated products 5 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter typical operating characteristics (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2 f f, c vcc = 1 f f , v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , unless otherwise noted.) en / uvlo threshold vs. temperature MAX17502 toc07 temperature (c) en / uvlo threshold voltage (v) 100 80 40 60 02 0 -20 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.12 -40 120 falling threshold rising threshold output voltage vs. temperature (MAX17502e) MAX17502 toc08 temperature (c) output voltage (v) 100 full load no load 80 -20 02 04 06 0 3.285 3.290 3.295 3.300 3.305 3.310 3.315 3.320 3.280 -40 120 efficiency vs. load current (MAX17502e) MAX17502 toc01 load current (ma) efficiency (%) 900 800 200 300 400 600 500 700 60 65 70 75 80 85 90 95 55 100 1000 v in = 12v v in = 24v v in = 36v v in = 48v efficiency vs. load current (MAX17502f) MAX17502 toc02 efficiency (%) 70 75 80 85 90 95 65 load current (ma) 900 800 200 300 400 600 500 700 100 1000 v in = 12v v in = 24v v in = 36v v in = 48v output voltage vs. load current (MAX17502e) MAX17502 toc03 output voltage (v) v in = 48v v in = 36v v in = 24v v in = 12v 3.292 3.294 3.296 3.298 3.300 3.302 3.304 3.306 3.308 3.310 3.290 load current (ma) 900 800 200 300 400 600 500 700 0 1000 100 output voltage vs. load current (MAX17502f) MAX17502 toc04 load current (ma) output voltage (v) 800 700 600 500 400 300 200 100 4.980 4.985 4.990 4.995 5.000 5.005 4.975 0 900 1000 v in = 12v v in = 24v v in = 36v v in = 48v shutdown current vs. temperature MAX17502 toc05 temperature (c) shutdown current (a) 100 80 -20 0 20 40 60 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 0.70 -40 120 no-load switching current vs. temperature MAX17502 toc06 temperature (c) no-load switching current (ma) 120 100 80 60 40 20 0 -20 4.85 4.90 4.95 5.00 4.80 -40 output voltage vs. temperature (MAX17502f) MAX17502 toc09 temperature (c) output voltage (v) 120 100 full load no load 60 80 02 04 0 -20 4.96 4.97 4.98 4.99 5.00 5.01 5.02 5.03 5.04 5.05 4.95 -40
????????????????????????????????????????????????????????????????? maxim integrated products 6 typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2 f f, c vcc = 1 f f , v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , unless otherwise noted.) soft-start/ shutdown from en/uvlo (MAX17502e) MAX17502 toc13 en / uvlo 2v/div v out 1v/div i out 500ma /div 1ms /div reset 2v/div runaway current limit vs. temperature MAX17502 toc11 temperature (c) runaway current limit (a) 120 100 60 80 0 20 40 -20 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 1.0 -40 soft-start from v in (MAX17502e) MAX17502 toc15 v in 20v/div i out 500ma /div v out 1v/div 400s/div reset 2v/div soft-start/ shutdown from en/uvlo (MAX17502f) MAX17502 toc14 en / uvlo 2v/div v out 2v/div i out 500ma /div 1ms /div reset 5v / div switching frequency vs. temperature MAX17502 toc12 temperature (c) switching frequency (khz) 120 100 60 80 0 20 40 -20 520 540 560 580 600 620 640 660 680 700 500 -40 MAX17502 toc10 temperature (c) peak current limit (a) peak current limit vs. temperature 1.2 1.4 1.6 1.8 2.0 1.0 120 100 80 60 40 20 0 -20 -40 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter
????????????????????????????????????????????????????????????????? maxim integrated products 7 typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2 f f, c vcc = 1 f f , v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , unless otherwise noted.) soft-start with 2v prebias (MAX17502e) MAX17502 toc17 en / uvlo 2v/div v out 1v/div 400s /div reset 2v/div load transient response of MAX17502e (load current stepped from no load to 500ma) MAX17502 toc19 v out (ac) 50mv/div i out 200ma / div 20s /div soft-start with 2.5v prebias (MAX17502f) MAX17502 toc18 en / uvlo 2v/div v out 1v/div 400s / div reset 5v/div load transient response of MAX17502f (load current stepped from no load to 500ma) MAX17502 toc20 v out (ac) 100mv/div i out 200ma /div 20s /div soft-start from v in (MAX17502f) MAX17502 toc16 v in 20v/div i out 500ma /div v out 2v/div 400s / div reset 5v/div MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter
????????????????????????????????????????????????????????????????? maxim integrated products 8 typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2 f f, c vcc = 1 f f , v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , unless otherwise noted.) bode plot of MAX17502e at 1a load MAX17502 toc25 45 67 89 1 23 45 67 89 12 bw = 63khz pm = 57 load transient response of MAX17502f (load current stepped from 500ma to 1a) MAX17502 toc21 v out (ac) 50mv/div i out 500ma /div 20s / div switching waveforms of MAX17502f at 1a load MAX17502 toc23 v out (ac) 50mv/div lx 20v/div i lx 500ma /div 2s/div bode plot of MAX17502f at 1a load MAX17502 toc26 45 67 89 1 23 45 67 89 12 bw = 61khz pm = 64 load transient response of MAX17502f (load current stepped from 500ma to 1a) MAX17502 toc22 v out (ac) 100mv/div i out 500ma /div 20s /div output overloaod protection of MAX17502f MAX17502 toc24 v out 500mv/div i out 500ma /div 20ms/div MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter
????????????????????????????????????????????????????????????????? maxim integrated products 9 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter pin configuration pin description pin name function 1 pgnd power ground. connect pgnd externally to the power ground plane. connect gnd and pgnd pins together at the ground return path of the v cc bypass capacitor. 2 v in power-supply input. the input supply range is from 4.5v to 60v. 3 en/uvlo enable/undervoltage lockout input. drive en/uvlo high to enable the output voltage. connect to the center of resistive divider between v in and gnd to set the input voltage (undervoltage threshold) at which the device turns on. pull up to v in for always on. 4 v cc 5v ldo output. bypass v cc with 1 f f ceramic capacitance to gnd. 5 fb feedback input. directly connect fb to the output. 6 ss soft-start input. connect a capacitor from ss to gnd to set the soft-start time. 7 n.c no connection. leave unconnected. 8 reset open-drain reset output. the reset output is driven low if fb drops below 92.5% of its set value. reset goes high 1024 clock cycles after fb rises above 95.5% of its set value. 9 gnd analog ground 10 lx switching node. connect lx to the switching side of the inductor. lx is high impedance when the device is in shutdown mode. ep exposed pad. connect to gnd pin of the ic. connect to a large copper plane below the ic to improve heat dissipation capability. top view *ep = exposed pad, connected to gnd tdfn (3mm x 2mm) MAX17502 1 2 3 4 5 pgnd v in en /uvlo v cc fb lx gnd reset n.c. ss + ep* 10 9 8 7 6
???????????????????????????????????????????????????????????????? maxim integrated products 10 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter block diagram pgnd lx v in v cc ldo slope compensation start reset logic reference switchover logic comp current sense p driver pwm logic g m gnd internal compensation n driver v cc 5a ss reset ss hiccup comp hiccup clk osc pwm comparator en/uvlo ss 900mv fb MAX17502
???????????????????????????????????????????????????????????????? maxim integrated products 11 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter detailed description the MAX17502 step-down regulator operates from 4.5v to 60v and delivers up to 1a load current. output voltage regulation accuracy meets q 1.6% over temperature. the device uses a peak-current-mode-control scheme. it employs synchronous rectification. an internal transcon - ductance error amplifier produces an integrated error voltage. the error voltage sets the duty cycle using a pwm comparator, a high-side curent-sense amplifier, and a slope-compensation generator. at each rising edge of the clock, the high-side p-channel mosfet turns on and remains on until either the appropriate or maximum duty cycle is reached, or the peak-current limit is detected. during the high-side mosfets on-time, the inductor current ramps up. during the second half of the switching cycle, the high-side mosfet turns off and the low-side n-channel mosfet turns on. the inductor releases the stored energy as its current ramps down, and provides current to the output (the internal low r dson pmos/ nmos switches ensure high efficiency at full load). this device also integrates enable/undervoltage lockout (en/uvlo), adjustable soft-start time (ss), and open- drain reset output ( reset ) functionality. linear regulator (v cc ) an internal linear regulator (v cc ) provides a 5v nominal supply to power the internal blocks and the low-side mosfet driver. the output of the v cc linear regula - tor should be bypassed with a 1 f f ceramic capacitor to gnd. the device employs an undervoltage-lockout circuit that disables the internal linear regulator when v cc falls below 3.7v (typ). the 300mv uvlo hyster - esis prevents chattering on power-up/power-down. the internal v cc linear regulator can source up to 40ma (typ) to supply the device and to power the low-side gate driver. switching frequency the device has a fixed 600khz switching frequency. the minimum duty ratio at which the device can operate is 7.7%. overcurrent protection /hiccup mode the device is provided with a robust overcurrent- protection scheme that protects the device under overload and output short-circuit conditions. a cycle-by-cycle peak-current limit turns off the high-side mosfet whenever the high-side switch current exceeds an internal limit of 1.6a (typ). a runaway-current limit on the high-side switch current at 1.8a (typ) protects the device under high input voltage, short-circuit conditions when there is insufficient output voltage available to restore the inductor current that built up during the on period of the step-down converter. one occurrence of the runaway-current limit triggers a hiccup mode. in addition, if due to a fault condition, output voltage drops to 71.1% (typ) of its nominal value any time after soft-start is complete, and hiccup mode is triggered. in hiccup mode, the converter is protected by suspending switching for a hiccup timeout period of 32,768 clock cycles. once the hiccup timeout period expires, soft-start is attempted again. reset output the device includes a reset comparator to monitor the output voltage. the open-drain reset output requires an external pullup resistor. reset can sink 2ma of current while low. reset goes high (high impedance) 1024 switching cycles after the regulator output increases above 95.5% of the designed nominal regulated voltage. reset goes low when the regulator output voltage drops to below 92.5% of the nominal regulated voltage. reset goes low during thermal shutdown. prebiased output when the device starts into a prebiased output, both the high-side and low-side switches are turned off so that the converter does not sink current from the output. high-side and low-side switches do not start switching until the pwm comparator commands the first pwm pulse, at which point switching commences first with the high-side switch. the output voltage is then smoothly ramped up to the target value in alignment with the internal reference. thermal-overload protection thermal-overload protection limits total power dissipa - tion in the device. when the junction temperature of the device exceeds +165 n c, an on-chip thermal sensor shuts down the device, allowing the device to cool. the thermal sensor turns the device on again after the junction temperature cools by 10 n c. soft-start resets during thermal shutdown. carefully evaluate the total power dissipation (see the power dissipation section) to avoid unwanted triggering of the thermal-overload protection in normal operation.
???????????????????????????????????????????????????????????????? maxim integrated products 12 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter applications information input capacitor selection the discontinuous input-current waveform of the buck converter causes large ripple currents in the input capacitor. the switching frequency, peak inductor current, and the allowable peak-to-peak voltage ripple that reflects back to the source dictate the capacitance requirement. the devices high switching frequency allows the use of smaller value input capacitors. x7r capacitors are recommended in industrial applications for their temperature stability. a minimum value of 2.2 f f should be used for the input capacitor. higher values help reduce the ripple on the input dc bus further. in applications where the source is located distant from the device input, an electrolytic capacitor should be added in parallel to the 2.2 f f ceramic capacitor to provide necessary damping for potential oscillations caused by the longer input power path and input ceramic capacitor. inductor selection three key inductor parameters must be specified for operation with the device: inductance value (l), inductor saturation current (i sat ), and dc resistance (r dcr ). to determine the inductance value, select the ratio of inductor peak-to-peak ripple current to the dc average current (lir). for lir values that are too high, the rms currents are high, and therefore the inductor i 2 r losses are high. for lir values that are too low, the inductance values are high and consequently the inductor dc resistance is also high, and therefore inductor i 2 r losses are high as well. a good compromise between size and loss is a 30% peak-to-peak ripple current to average-current ratio (lir = 0.3). the switching fre - quency, input voltage, output voltage, and selected lir determine the inductor value as follows: out in out in sw out v (v - v ) l= v f i lir where v in , v out , and i out are nominal values. the switching frequency is 600khz for the device. select a low-loss inductor closest to the calculated value with acceptable dimensions and having the lowest possible dc resistance. the saturation current rating (i sat ) of the inductor must be high enough to ensure that saturation can occur only above the peak current-limit value (i peak-limit (typ) = 1.6a for the device). a variety of inductors from different suppliers are available to meet this requirement (e.g., inductors from the coilcraft lps6235 series). see t able 1 to select inductors for 5v and 3.3v fixed output-voltage applications based on the max17 502e / MAX17502f. output capacitor selection x7r cer amic output capacitors are preferred due to their stability over temperature in industrial applications. the output capacitor is usually sized to support a step load of 50% of the maximum output current in the application, such that the output-voltage deviation is contained to 3% of the output-voltage change. the output capacitance can be calculated as follows: step response out out response c sw 1i t c 2v 0.33 1 t () ff = ? ?+ where i st ep is the load current step, t response is the response time of the controller, d v out is the allowable output-voltage deviation, and f c is the target closed-loop crossover frequency. f c is generally chosen to be 1/8 to 1/10 of f sw . use table 2 to select output capacitors for fixed 5v and 3.3v output-voltage applications based on the MAX17502e/MAX17502f. table 1. inductor selection v out (v) i out (max) (ma) l (h) minimum i sat (a) suggested part 5 1 22 1.6 coilcraft lps6235-223ml_ 3.3 1 15 1.6 coilcraft lps6235-153ml_
???????????????????????????????????????????????????????????????? maxim integrated products 13 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter soft-start capacitor selection the device implements adjustable soft-start operation for the synchronous step-down converter. a capacitor connected from the ss pin to gnd programs the soft-start period. the soft-start time (t ss ) is related to the capacitor con - nected at ss (c ss ) by the following equation: ss ss c 5.55 t = where t ss is in milliseconds and c ss is in nanofarads. for example, to have a 1.8ms soft-start time, a 10nf capaci - tor shoul d be connected from the ss pin to gnd. setting the input undervoltage- lockout level the device offers an adjustable input undervoltage- lockout level. set the voltage at which the device turns on, with a resistive voltage-divider connected from v in to gnd (see figure 1). connect the center node of the divider to en/uvlo. choose r1 to be 3.3m i and then calculate r2 as follows: inu r1 1.218 r2 (v -1.218) = where v inu is the voltage at which the device is required to turn on. power dissipation it should be ensured that the junction temperature of the device does not exceed 125 n c under the operating conditions specified for the power supply. at a particular operating condition, the power losses that lead to temperature rise of the part are estimated as follows: ( ) 2 loss out dcr out out out out 1 p p -1 - i r p vi ?? ?? = ?? ?? ?? ?? ?? = where p out is the output power, e is is the efficiency of the device, and r dcr is the dc resistance of the output inductor (see the typical operating characteristics for more information on efficiency at typical operating conditions). the maximum power that can be dissipated in the devices 10-pin tdfn-ep package is 1188.7mw at +70 n c temperature. the power dissipation capability should be derated as the temperature goes above +70 n c at 14.9mw/ n c. for a multilayer board, the thermal performance metrics for the package are given below: b ja = 67.3 n c/w b jc = 18.2 n c/w the junction temperature of the device can be estimated at any given maximum ambient temperature (t a_max ) from the following equation: ( ) j_max a_max ja loss tt p = + if the application has a thermal-management system that ensures that the exposed pad of the device is maintained at a given temperature (t ep_max ) by using proper heat sinks, then the junction temperature of the device can be estimated at any given maximum ambient temperature from the following equation: ( ) j_max ep_max jc loss tt p = + table 2. output capacitor selection figure 1. adjustable uvlo network v out (v) i out (max) (a) type voltage rating (v) suggested part 5 1 10 f f/1210/x7r 10 murata grm32dr71a106ka01l 3.3 1 22 f f/1210/x7r 10 murata grm32er71a226ke20l v in en / uvlo gnd r2 r1
???????????????????????????????????????????????????????????????? maxim integrated products 14 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter pcb layout guidelines all connections carrying pulsed currents must be very short and as wide as possible. the inductance of these connections must be kept to an absolute minimum due to the high di/dt of the currents. since inductance of a current-carrying loop is proportional to the area enclosed by the loop, if the loop area is made very small, inductance is reduced. additionally, small-current loop areas reduce radiated emi. a ceramic input filter capacitor should be placed close to the v in pin of the device. this eliminates as much trace inductance effects as possible and gives the device a cleaner voltage supply. the bypass capacitor for the v cc pin should also be placed close to the pin to reduce effects of trace impedance. the feedback trace should be routed as far as possible from the inductor. when routing the circuitry around the device, the analog small-signal ground and the power ground for switching currents must be kept separate. they should be connected together at a point where switching activity is at minimum, typically the return terminal of the v cc bypass capacitor. this helps to keep the analog ground quiet. the ground plane should be kept continuous/ unbroken as much as possible. no trace carrying high switching current should be placed directly over any ground plane discontinuity. pcb layout also affects the thermal performance of the design. a number of thermal vias that connect to a large ground plane should be provided under the exposed pad of the device, for efficient heat dissipation. several vias in parallel have lower impedance than a single via. for a sample layout that ensures first-pass success, refer to the MAX17502 evaluation kit layout available at www.maxim-ic.com .
???????????????????????????????????????????????????????????????? maxim integrated products 15 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter typical applications circuits figure 2. MAX17502f application circuit (5v output, 1a maximum load current, 600khz switching frequency) figure 3. MAX17502e application circuit (3.3v output, 1a maximum load current, 600khz switching frequency) c2 1f c3 3300pf n.c. ss v cc en / uvlo v in lx pgnd gnd fb reset v in 24v 20% c1 2.2f 1210 1 2 ju1 r1 3.32mi r2 866ki 3 MAX17502f reset l1 22h c4 10f, 10v 1210 v out 5v, 1a c2 1f c3 3300pf n.c. ss v cc en / uvlo v in lx pgnd gnd fb reset v in 24v 20% c1 2.2f 1210 1 2 ju1 r1 3.32mi r2 866ki 3 MAX17502e reset l1 15h c4 22f, 10v 1210 v out 3.3v, 1a
???????????????????????????????????????????????????????????????? maxim integrated products 16 MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter ordering information /selector guide + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad. note: all devices are specified over the -40c to +125c operating temperature range. optional variants available to support adjustable output and pfm. contact your maxim sales representative for more information. package information for the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status. chip information process: bicmos part pin-package output voltage switching frequency peak-current- mode control scheme output current MAX17502eatb+ 10 tdfn-ep* 3.3v 600khz forced pwm 1a MAX17502fatb+ 10 tdfn-ep* 5v 600khz forced pwm 1a package type package code outline no. land pattern no. 10 tdfn-ep t1032n+1 21-0429 90-0082
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. 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 products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 17 ? 2012 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 5/12 initial release MAX17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter

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