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general description the max17501 high-efficiency, high-voltage, synchro nous step-down dc-dc converter with integrated mosfets operates over a 4.5v to 60v input voltage range. it deliv - ers output currents up to 500ma at output voltages of 0.9v to 92%v in . the output voltage is accurate to within 1.7% over -40c to +125c. the max17501 is avail - able in a compact tdfn package. simulation models are available. the device features peak-current-mode control with pulse-width modulation (pwm). users can choose devic - es with either pulse frequency modulation (pfm) or forced pwm scheme. pfm devices skip pulses at light load for higher efficiency, while forced-pwm devices operate with fixed switching frequency at any load for noise sensi - tive-applications. the low-resistance, on-chip mosfets ensure high efficiency at full load and simplify the layout. a programmable soft-start feature allows users to reduce input inrush current. 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 system upon achieving successful regulation of the output voltage. applications industrial process control hvac and building control base station, voip, telecom home theatre automotive battery-powered equipment general-purpose point-of-load benefts and features eliminates external components and reduce total cost ? no schottky-synchronous operation for high efficiency and reduced cost ? internal compensation and feedback divider for 3.3v and 5v outputs ? a ll-ceramic capacitors, ultra-compact layout reduces number of dc-dc regulators to stock ? wide 4.5v to 60v input voltage range ? 0.9v to 92%v in output voltage ? delivers up to 500ma ? 600khz and 300khz switching frequency options ? available in a 10-pin, 3mm x 2mm tdfn package reduces power dissipation ? peak efficiency > 90% ? pfm feature for high light-load efficiency ? shutdown current = 0.9a (typ) operates reliably in adverse industrial environments ? hiccup-mode current limit, sink current limit, and autoretry startup ? built-in output-voltage monitoring (open-drain reset pin) ? resistor-programmable en/uvlo threshold ? adjustable soft-start and prebiased power-up ? -40c to +125c industrial temperature range 19-6244; rev 2; 1/13 ordering information appears at end of data sheet. for related parts and recommended products to use with this part, refer to www.maximintegrated.com/max17501.related . max17501 60v, 500ma, ultra-small, high-efficiency, synchronous step-down dc-dc converter
maxim integrated 2 electrical characteristics (v in = 24v, v gnd = v pgnd = 0v, c vin = c vcc = 1f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected. t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to gnd, unless otherwise noted.) (note 2) 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.maximintegrated.com/thermal-tutorial . 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 (v in + 0.3v) 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......................................................... 1.6a output short-circuit duration.....................................continuous continuous power dissipation (t a = +70c) (derate 14.9mw/c above +70c) (multilayer board) .1188.7mw operating temperature range......................... -40c to +125c junction temperature......................................................+150c storage temperature range............................. -65c to +160c lead temperature (soldering, 10s).................................+300c soldering temperature (reflow).......................................+260c 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 ab solute maximum rating conditions for extended periods may affect device reliability. package thermal characteristics (note 1) tdfn junction-to-ambient thermal resistance ( ja ) ....... 67.3c/w junction-to-case thermal resistance ( jc ) ............ 18.2c/w absolute maximum ratings 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 a i in-hibernate v fb = 1.03 x v out , max17501a/b 90 145 i in-sw normal switching mode, no load max17501e/f/g 4.75 6.75 ma max17501h 2.5 3.6 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 0.7 en input leakage current i en v en = v in = 60v, t a = +25c 8 200 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 15 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 max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 3 electrical characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = c vcc = 1f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected. t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to gnd, unless otherwise noted.) (note 2) parameter symbol conditions min typ max units power mosfets high-side pmos on-resistance r ds-onh i lx = 0.5a (sourcing) t a = +25c 0.55 0.85 t a = t j = +125c (note 3) 1.2 low-side nmos on-resistance r ds-onl i lx = 0.5a (sinking) t a = +25c 0.2 0.35 t a = t j = +125c (note 3) 0.47 lx leakage current i lx_lkg v en = 0v, t a = +25c, v lx = (v pgnd + 1v) to (v in - 1v) 1 a soft-start (ss) charging current i ss v ss = 0.5v 4.7 5 5.3 a feedback (fb/vo) fb regulation voltage v fb_reg max17501g/h 0.884 0.9 0.916 v fb input bias current i fb t a = +25 n c max17501a/e, v fb = 3.3v 6.8 12 17 a max17501b/f, v fb = 5v 6.8 12 17 max17501g/h, v fb = 0.9v 100 na output voltage (v out ) output voltage range v out max17501a/e 3.248 3.3 3.352 v max17501b/f 4.922 5 5.08 max17501g 0.9 0.92 x v in max17501h 0.9 0.965 x v in v out threshold for entering hibernate mode v fb_hbr v fb rising, max17501a/b 103.3 % v out threshold for exiting hibernate mode v fb_hbf v fb falling, max17501a/b 101.3 % transconductance amplifier (comp) transconductance g m i comp = 2.5 a, max17501g/h 510 590 650 s comp source current i comp_src max17501g/h 19 32 55 a comp sink current i comp_sink max17501g/h 19 32 55 a current-sense transresistance r cs max17501g/h 0.9 1 1.1 v/a max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 4 electrical characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = c vcc = 1f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected. t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to gnd, unless otherwise noted.) (note 2) note 2: all limits are 100% tested at +25c. limits over temperature are guaranteed by design. note 3: guaranteed by design, not production tested. parameter symbol conditions min typ max units current limit peak current-limit threshold i peak-limit 0.64 0.76 0.86 a runaway current-limit threshold i runaway- limit 0.65 0.78 0.905 a sink current-limit threshold i sink-limit max17501a/b 0.03 a max17501e/f/g/h 0.3 0.35 0.4 pfm current-limit threshold i pfm max17501a/b 0.125 a timings switching frequency f sw v fb > v out- hicf max17501a/b/e/f/g 560 600 640 khz max17501h 280 300 320 v fb < v out-hicf 280 300 320 events to hiccup after crossing runaway current limit 1 event 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 75 120 ns maximum duty cycle d max v fb = 0.98 x v fb-reg max17501a/b/e/f/g 92 94 96 % max17501h 96.5 97.5 98.5 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 fb-reg , t a = +25c 0.45 a v out threshold for reset falling v out-okf v fb falling 90.5 92.5 94.5 % v out threshold for reset rising v out-okr v fb rising 93.5 95.5 97.5 % reset delay after fb reaches 95% regulation v fb rising 1024 cycles thermal shutdown thermal-shutdown threshold temperature rising 165 c thermal-shutdown hysteresis 10 c max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 5 typical operating characteristics (v in = 24v, v gnd = v pgnd = 0v, c vin = c vcc = 1f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected, t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to gnd, unless otherwise noted.) efficiency vs. load curren t (max17501a) load current (ma) efficiency (% ) 100 10 40 50 60 70 80 90 100 30 1 v in = 12v v in = 24v v in = 36v max17501 toc01 efficiency vs. load curren t (max17501b) load current (ma) efficiency (% ) 100 10 40 50 60 70 80 90 100 30 1 v in = 12v v in = 24v v in = 36v v in = 48v max17501 toc02 efficiency vs. load curren t (max17501e) load current (ma) efficiency (% ) 450 400 300 350 150 200 250 100 50 55 60 65 70 75 80 85 90 95 45 50 500 v in = 36v v in = 24v v in = 12v max17501 toc03 efficiency vs. load curren t (max17501f) load current (ma) efficiency (% ) 450 400 300 350 150 200 250 100 50 60 70 80 90 100 40 50 500 v in = 48v v in = 12v v in = 36v v in = 24v max17501 toc04 output voltage vs. load current (max17501a) load current (ma) output voltage (v) 450 400 350 300 250 200 150 100 50 3.30 3.35 3.40 3.45 3.25 0 500 v in = 36v v in = 24v v in = 12v max17501 toc05 output voltage vs. load current (max17501b) load current (ma) output voltage (v) 450 400 350 300 250 200 150 100 50 4.95 5.15 5.10 5.05 5.00 5.20 4.90 0 500 v in = 12v v in = 24v v in = 36v v in = 48v max17501 toc0 6 output voltage vs. load current (max17501e) load current (ma) output voltage (v) 450 400 350 300 250 200 150 100 50 0 500 3.295 3.300 3.305 3.310 3.315 3.320 3.290 v in = 24v v in = 12v v in = 36v max17501 toc07 output voltage vs. load current (max17501f) load current (ma) output voltage (v) 450 400 350 300 250 200 150 100 50 0 500 4.97 4.96 4.98 4.99 5.00 5.01 5.03 5.02 5.04 5.05 4.95 v in = 48v v in = 36v v in = 24v v in = 12v max17501 toc08 shutdown current vs. temperature max17501 toc09 temperature (c) shutdown current (a) 1001 20 80 60 40 20 0 -20 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 0.70 -40 www.maximintegrated.com max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter
maxim integrated 6 typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = c vcc = 1f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected, t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to gnd, unless otherwise noted.) no-load switching current vs. temperature (pfm operation) max17501 toc10 temperature (c) no-load switching current (a) 100 120 80 60 40 20 0 -20 60 80 100 120 140 40 -40 no-load switching current vs. temperature (forced-pwm operation) max17501 toc11 temperature (c) no-load switching current (ma) 100 120 80 60 40 20 0 -20 4.85 4.90 4.95 5.00 4.80 -40 en/uvlo threshol d vs. temperature max17501 toc12 temperature (c) en/uvlo threshold voltage (v ) 100 120 80 60 40 20 0 -20 1.13 1.14 1.16 1.18 1.20 1.23 1.22 1.21 1.19 1.17 1.15 1.12 -40 rising threshold fa lling threshold no-load output voltage vs. temperature (max17501e ) max17501 toc13 temperature (c) output voltage (v) 100 120 80 60 40 20 0 -20 3.275 3.300 3.325 3.350 3.250 -40 no-load output voltage vs. temperature (max17501f ) max17501 toc14 temperature (c) output voltage (v) 100 120 80 60 40 20 0 -20 4.975 5.000 5.025 5.050 4.950 -40 feedback voltage vs. temperature max17501 toc15 temperature (c) feedback voltage (v) 100 120 80 60 40 20 0 -20 0.89 0.90 0.91 0.92 0.88 -40 peak and runaway current limit vs. temperature max17501 toc16 temperature (c) current limit (a ) 100 120 80 60 40 20 0 -20 0.75 0.70 0.65 0.80 0.85 0.90 0.60 -40 peak current limit runa wa y current limit switching frequenc y vs. temperatur e max17501 toc17 temperature (c) switching frequency (khz ) 100 120 80 60 40 20 0 -20 400 300 500 600 700 200 -40 no-load soft-start from en/uvl o (max17501a) max17501 toc18 1ms/div en/uvlo 2v/div v out 1v/div reset 2v/div www.maximintegrated.com max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter
maxim integrated 7 typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = c vcc = 1f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected, t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to gnd, unless otherwise noted.) no-load soft-start from en/uvl o (max17501b) max17501 toc19 1ms/div en/uvlo 2v/div v out 2v/div reset 5v/div full-load soft-start/shutdown from en/uvl o (max17501e) max17501 toc20 1ms/div en/uvlo 2v/div v out 1v/div i out 200ma/div reset 2v/div full-load soft-start/shutdown from en/uvl o (max17501f) max17501 toc21 1ms/div en/uvlo 2v/div v out 2v/div i out 200ma/div reset 5v/div no-load soft-start from v in (max17501a) max17501 toc22 400s/div v in 20v/div v out 1v/div reset 2v/div no-load soft-start from v in (max17501b) max17501 toc23 400s/div v in 20v/div v out 2v/div reset 5v/div full-load soft-start from v in (max17501e) max17501 toc24 400s/div v in 20v/div v out 1v/div i out 200ma/div reset 2v/div www.maximintegrated.com max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter
maxim integrated 8 typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = c vcc = 1f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected, t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to gnd, unless otherwise noted.) full-load soft-start from v in (max17501f) max17501 toc25 400s/div v in 20v/div v out 2v/div i out 200ma/div reset 5v/div soft-start with 2v prebia s (max17501a) max17501 toc26 400s/div en/uvlo 2v/div v out 1v/div reset 2v/div soft-start with 2.5v prebia s (max17501b) max17501 toc27 400s/div en/uvlo 2v/div v out 1v/div reset 5v/div soft-start with 2v prebia s (max17501e) max17501 toc28 400s/div en/uvlo 2v/div v out 1v/div reset 2v/div soft-start with 2.5v prebia s (max17501f) max17501 toc29 400s/div en/uvlo 2v/div v out 1v/div reset 5v/div load transient response of max17501a (load current stepped from 5ma to 255ma) max17501 toc30 200s/div v out (ac) 100mv/div i out 100ma/div www.maximintegrated.com max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter
maxim integrated 9 typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = c vcc = 1f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected, t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to gnd, unless otherwise noted.) load transient response of max17501b (load current stepped from 5ma to 255ma) max17501 toc31 200s/div v out (ac) 100mv/div i out 100ma/div load transient response of max17501e (load current stepped from no-load to 250ma ) max17501 toc32 20s/div v out (ac) 50mv/div i out 100ma/div load transient response of max17501f (load current stepped from no-load to 250ma ) max17501 toc33 20s/div v out (ac) 100mv/div i out 100ma/div load transient response of max17501f (load current stepped from 250ma to 500ma) max17501 toc35 20s/div v out (ac) 100mv/div i out 200ma/div load transient response of max17501e (load current stepped from 250ma to 500ma) max17501 toc34 20s/div v out (ac) 50mv/div i out 200ma/div switching waveforms of max17501f at 500ma load max17501 toc36 2s/div v out (ac) 50mv/div i lx 500ma/div lx 10v/div www.maximintegrated.com max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter
maxim integrated 10 typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = c vcc = 1f, v en = 1.5v, c ss = 3300pf, v fb = 0.98 x v out , lx = unconnected, reset = unconnected, t a = t j = -40c to +125c, unless otherwise noted. typical values are at t a = +25c. all voltages are referenced to gnd, unless otherwise noted.) switching waveforms of max17501a at 15ma load max17501 toc37 10s/div v out (ac) 100mv/div i lx 100ma/div lx 10v/div output overload protectio n of max17501f max17501 toc38 20ms/div v out 2v/div i out 200ma/div bode plot of max17501e at 500ma load max17501 toc39 f cr = 51khz pm = 55 45 67 89 12 bode plot of max17501f at 500ma load max17501 toc40 f cr = 49.8khz pm = 62 45 67 89 12 www.maximintegrated.com max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter
maxim integrated 11 pin description pin confguration 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 the 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 1f ceramic capacitance to gnd. 5 fb/vo feedback input. for fxed output voltage devices, directly connect fb/vo to the output. for adjustable output voltage devices, connect fb/vo to the center of the resistive divider between v out and gnd. 6 ss soft-start input. connect a capacitor from ss to gnd to set the soft-start time. 7 n.c./comp for fxed output voltage devices, leave this pin unconnected. for adjustable output voltage devices, connect an rc network from comp to gnd. 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. reset is valid when the device is enabled and v in is above 4.5v. 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 the gnd pin of the ic. connect to a large copper plane below the ic to improve heat dissipation capability. top view *ep = exposed pad. connect to gn d tdfn (3mm x 2mm) max17501 1 2 3 4 5 pgnd v in en / uvlo v cc fb /v o lx gnd reset n.c./ comp ss + ep* 10 9 8 7 6 max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 12 block diagram pgnd lx v in v cc ldo slope compensa tion st ar t reset logic reference switchover logic comp current sense p driver pwm, pfm logic g m gnd internal compensa tion (for a, b, e, f versions) n driver v cc 5a ss reset n.c. /comp ss hiccup comp hiccup clk osc pwm comp arat or en ss 900mv fb max17501 max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 13 detailed description the max17501 synchronous step-down regulator oper - ates from 4.5v to 60v and delivers up to 500ma load current. output voltage regulation accuracy meets 1.7% over temperature. the device uses a peak-current-mode control scheme. an internal transconductance error amplifier generates an integrated error voltage. the error voltage sets the duty cycle using a pwm comparator, a high-side current-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 and remains on until either the next rising edge of the clock arrives or sink current limit is detected. 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. pfm operation the a and b versions of the max17501 feature a pfm scheme to improve light load efficiency. at light loads, once the part enters pfm mode, the inductor current is forced to a fixed peak of 125ma (typical) every clock cycle until the output rises to 103.3% of nominal voltage. once output reaches 103.3% of nominal voltage, both high- side and low-side fets are turned off and the part enters hibernate operation until the load discharges output to 101.3% of nominal voltage. most of the internal blocks are turned off in hibernate operation to save quiescent current. such an operation reduces the effective switch - ing frequency of the converter at light loads, resulting in reduced switching losses and improved light load effi - ciency. the part naturally exits pfm mode when the load current exceeds 62.5ma (typical). 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 regulator should be bypassed with a 1f ceramic capacitor to gnd. the device employs an undervoltage-lockout circuit that disables the internal linear regulator when v cc falls below 3.7v (typical). the internal v cc linear regulator can source up to 40ma (typical) to supply the device and to power the low-side gate driver. operating input voltage range the maximum operating input voltage is determined by the minimum controllable on-time and the minimum oper - ating input voltage is determined by the maximum duty cycle and circuit voltage drops. the minimum and maxi - mum operating input voltages for a given output voltage should be calculated as: out out(max) dcr in(min) max out(max) v (i (r 0.47)) v d (i 0.73) + + = + = out in(max) sw (max) on(min) v v ft where v out is the steady-state output voltage, i out(max) is the maximum load current, r dcr is the dc resistance of the inductor, f sw(max) is the switching frequency (max - imum) and t on(min) is the worst-case minimum switch on-time (120ns). the following table lists the f sw(max) and d max values to be used for calculation for different versions of the max17501: overcurrent protection/hiccup mode the device is provided with a robust overcurrent-pro - tection 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 760ma (typ). a runaway current limit on the high-side switch current at 780ma (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 condi - tion, output voltage drops to 71.14% (typ) of its nominal value any time after soft-start is complete, hiccup mode is triggered. part version f sw (max) (khz) d max max17501a/b/e/f/g 640 0.92 max17501h 320 0.965 max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 14 in hiccup mode, the converter is protected by suspend - ing switching for a hiccup timeout period of 32,768 clock cycles. once the hiccup timeout period expires, soft-start is attempted again. this operation results in minimal power dissipation under overload fault conditions. 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 cur - rent while low. reset goes high (high impedance) 1024 switching cycles after the regulator output increases above 95.5% of the designated nominal regulated volt - age. reset goes low when the regulator output voltage drops to below 92.5% of the nominal regulated voltage. reset also goes low during thermal shutdown. reset is valid when the device is enabled and v in is above 4.5v. prebiased output when the device starts into a prebiased output, both the high-side and low-side switches are turned off so 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 +165c, an on-chip thermal sensor shuts down the device, allowing the device to cool. the thermal sensor turns the device on again after the junc tion temperature cools by 10c. 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. applications information input capacitor selection the discontinuous input-current waveform of the buck converter causes large ripple currents in the input capaci - tor. the switching frequency, peak inductor cur rent, 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 rec - ommended in industrial applications for their temperature stability. a minimum value of 1f 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 1f 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 ). the switching frequency, input voltage, and output voltage determine the inductor value as follows: = out in out in sw v (v - v ) l 0.15 v f where v in , v out , and f sw are nominal values. ensure that at any operating condition, the ratio (v out /(l x f sw )) is between 150ma and 250ma. select a low-loss inductor closest to the calculated value with acceptable dimensions and having the lowest pos - sible dc resistance. the saturation current rating (i sat ) of the inductor must be high enough to ensure that satu - ration can occur only above the peak current-limit value (i peak-limit (typ) = 0.76a for the device). output capacitor selection x7r ceramic 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, so the output-voltage deviation is contained to 3% of the output-voltage change. for fixed 3.3v and 5v output voltage versions, connect a minimum of 10f (1206) capacitor at the output. for adjustable output voltage versions, the output capaci - tance can be calculated as follows: = ? step response out out it 1 c 2v ?+ response c sw 0.33 1 t ff where i step is the load current step, t response is the response time of the controller, v out is the allowable output-voltage deviation, f c is the target closed-loop cross - over frequency, and f sw is the switching frequency. select f c to be 1/12th of f sw . consider dc bias and aging effects while selecting the output capacitor. max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 15 figure 1. setting the output voltage figure 2. adjustable en/uvlo network soft-start capacitor selection the max17501 implements adjustable soft-start opera - tion to reduce inrush current. a capacitor con nected 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 program a 600s soft-start time, a 3300pf capacitor should be connected from the ss pin to gnd. ensure that (c sel x v out /t ss ) is less than 150ma, where c sel is the selected output capacitance. adjusting output voltage the max17501a/e and max17501b/f have preset out - put voltages of 3.3v and 5.0v, respectively. connect fb/ vo directly to the positive terminal of the output capacitor (see the typical applications circuits ). the max17501g/h offer an adjustable output voltage. set the output voltage with a resistive voltage-divider con - nected from the positive terminal of the output capacitor (v out ) to gnd (see figure 1 ). connect the center node of the divider to fb/vo. to optimize efficiency and output accuracy, use the following procedure to choose the val - ues of r4 and r5: for max17501g, select the parallel combination of r4 and r5, rp to be less than 15k. for the max17501h, select the parallel combination of r4 and r5, rp to be less than 30k. once rp is selected, calculate r4 as: out rp v r4 0.9 = calculate r5 as follows: out r4 0.9 r5 (v - 0.9) = 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 2 ). connect the center node of the divider to en/uvlo. choose r1 to be 3.3m, and then calculate r2 as: inu r1 1.218 r2 (v - 1.218) = where v inu is the voltage at which the device is required to turn on. for adjustable output voltage devices, ensure that v inu is higher than 0.8 x v out . r5 r4 fb /v o gnd v out r2 r1 en/uvl o gnd v in max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 16 figure 3. external compensation network external loop compensation for adjustable output versions the max17501 uses peak current-mode control scheme and needs only a simple rc network to have a stable, high-bandwidth control loop for the adjustable output volt - age versions. the basic regulator loop is modeled as a power modulator, an output feedback divider, and an error amplifier. the power modulator has dc gain g mod(dc) , with a pole and zero pair. the following equation defines the power modulator dc gain: = ?? ++ ?? ?? mod(dc) load in sw sel 1 g 1 0.2 0.5 - d r vfl where r load = v out /i out(max) , f sw is the switching frequency, l sel is the selected output inductance, d is the duty ratio, d = v out/ v in . the compensation network is shown in figure 3 . r z can be calculated as: z c sel out r 12000 f c v = where r z is in . choose f c to be 1/12th of the switching frequency. c z can be calculated as follows: sel mod(dc) z z cg c r = c p can be calculated as follows: = p z sw 1 c - 5pf rf power dissipation the exposed pad of the ic should be properly soldered to the pcb to ensure good thermal contact. ensure the junction temperature of the device does not exceed +125c under the operating conditions specified for the power supply. at high ambient temperatures, based on the operating condition, the heat dissipated in the ic might exceed the maximum junction temperature of +125c. heat sink should be used to reduce ja at such operating condi - tions. for typical applications, refer to the temperature derating curves included in the max17501 evaluation kit data sheet. to prevent the part from exceeding 125c junction tem - perature, users need to do some thermal analysis. at a particular operating condition, the power losses that lead to temperature rise of the device are estimated as follows: ( ) 2 loss out dcr out 1 p (p ( - 1) ) - i r = out out out p vi = where p out is the output power, is is the efficiency of the device, and r dcr is the dc resistance of the output inductor (refer to the t ypical operating characteristics in the evaluation kit data sheets for more information on efficiency at typical operating conditions). the maximum power that can be dissipated in the 10-pin tdfn-ep package is 1188.7mw at +70c temperature. the power dissipation capability should be derated as the temperature goes above +70c at 14.9mw/c. for a typical multilayer board, the thermal performance metrics for the package are given as: ja 67.3 c w = jc 18.2 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 as: ( ) j_max ep_max jc loss tt p = + r z to comp pi n c z c p max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 17 pcb layout guidelines careful pcb layout is critical to achieve low switching loss - es and stable operation. for a sample layout that ensures first-pass success, refer to the max17501 evaluation kit layouts available at www.maximintegrated.com . follow these guidelines for good pcb layout: 1) all connections carrying pulsed currents must be very short and as wide as possible. the loop area of these connections must be made very small to reduce stray inductance and radiated emi. 2) a ceramic input filter capacitor should be placed close to the v in pin of the device. the bypass capacitor for the v cc pin should also be placed close to the v cc pin. external compensation components should be placed close to the ic and far from the inductor. the feedback trace should be routed as far as possible from the inductor. 3) the analog small-signal ground and the power ground for switch ing currents must be kept separate. they should be connected together at a point where switch - ing activity is at minimum, typically the return terminal of the v cc bypass capacitor. the ground plane should be kept continuous as much as possible. 4) 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. figure 4 and 5 show the recommended component place - ment for max17501. figure 4. recommended component placement for max17501a/b/e/f ep r4 c2 c1 r2 r1 v in plane pgnd plane gnd plane vias to bott om side pgnd plan e vias to bott om side v out track vias to bott om side gnd plan e l1 v out plane lx plane c3 reset c4 max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 18 figure 5. recommended component placement for max17501g/h ep r4 r5 c2 c1 r2 r1 v in plane pgnd plane gnd plane l1 v out plane lx plane c3 c9 c5 r3 reset vias to bott om side pgnd plan e vias to bott om side v out track vias to bott om side gnd plan e c4 max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 19 typical applications circuits figure 6. max17501a/e application circuit (3.3v output, 500ma maximum load current, 600khz switching frequency) figure 7. max17501b/f application circuit (5v output, 500ma maximum load current, 600khz switching frequency) c2 1f c3 3300pf n.c. ss v cc en / uvlo v in lx pgnd gnd fb /v o reset v in 24v c1 1f 1206 1 2 ju1 r1 3.32m r2 866k 3 max17501 reset l1 33h c4 10f , 1206 v out 3.3v , 500ma c2 1f c3 3300pf n.c. ss v cc en / uvlo v in lx pgnd gnd fb /v o reset v in 24v c1 1f 1206 1 2 ju1 r1 3.32m r2 866k 3 max17501 reset l1 47h c4 10f , 1206 v out 5v , 500ma max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 20 figure 8. max17501g application circuit (12v output, 500ma maximum load current, 600khz switching frequency) figure 9. max17501h application circuit (2.5v output, 500ma maximum load current, 300khz switching frequency) c2 1f c3 6800pf r3 27.4k c5 1200pf c9 10pf comp ss v cc en / uvlo v in lx pgnd gnd fb /v o reset v in 24v c1 1f 1206 1 2 ju1 r1 3.32m r2 316k 3 max17501 reset l1 100h c4 4.7f , 1206 v out 12v , 500ma r4 174k r5 14k c2 1f c3 6800pf r3 20k c5 2200pf c9 47pf comp ss v cc en / uvlo v in lx pgnd gnd fb /v o reset v in 24v c1 2.2f 1210 1 2 ju1 r1 3.32m r2 1m 3 max17501 reset l1 47h c4 22f , 1210 v out 2.5v , 500ma r4 69.8k r5 39.2k max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
maxim integrated 21 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 suffix character, but the drawing pertains to the package regardless of rohs status. chip information process: bicmos +denotes a lead(pb)-free/rohs-compliant package. *ep = exposed paddle. *ep = exposed pad. ordering information/part selector guide part pin-package output voltage (v) switching frequency (khz) mode MAX17501AATB+ 10 tdfn-ep* 3.3 600 pfm max17501batb+ 10 tdfn-ep* 5 600 pfm max17501eatb+ 10 tdfn-ep* 3.3 600 pwm max17501fatb+ 10 tdfn-ep* 5 600 pwm max17501gatb+ 10 tdfn-ep* adjustable 600 pwm max17501hatb+ 10 tdfn-ep* adjustable 300 pwm package type package code outline no. land pattern no. 10 tdfn t1032n+1 21-0429 90-0082 max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter www.maximintegrated.com
? 2013 maxim integrated products, inc. 22 revision history revision number revision date description pages changed 0 5/12 initial release 1 11/12 added max17501a, max17501b, max17501g, max17501h to data sheet 1C22 2 1/13 added explanation on detailed condition for reset 11, 14 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 specifcations 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 and the maxim integrated logo are trademarks of maxim integrated products, inc. max17501 60v, 500ma, ultra-small, high-effciency, synchronous step-down dc-dc converter for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim integrateds website at www.maximintegrated.com.

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