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max17502 60v, 1a, ultra-small, high-efficiency, synchronous step-down dc-dc converter general description the max17502 high-efficiency, high-voltage, synchro nous step-down dc-dc converter with integrated mosfets operates over a 4.5v to 60v input voltage range. this device is offered in a fixed 3.3v , 5v or adjustable output voltage (0.9v to 92%v in ) while delivering up to 1a of current. the output voltage is accurate to within 1.7% over -40c to +125c. the max17502 is available in compact tdfn and tssop packages. simulation models are available. the device features peak-current-mode control with pulse-width modulation (pwm) and operates with fixed switching frequency at any load. 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 battery-powered equipment general-purpose point-of-load beneits and features eliminates external components and reduces total cost ? no schottky-synchronous operation for high efficiency and reduced cost ? internal compensation and feedback divider for 3.3v and 5v fixed 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 adjustable output voltage ? delivers up to 1a ? 600khz and 300khz switching frequency options ? available in a 10-pin, 3mm x 2mm tdfn and 14-pin, 5mm x 4.4mm tssop packages reduces power dissipation ? peak efficiency > 90% ? 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 19-6245 rev 4; 6/15 ordering information/selector guide appears at end of data sheet. downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 2 electrical characteristics (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2f, 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 refer - enced 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 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 absolute maximum rating conditions for extended periods may affect device reliability. package thermal characteristics (note 1) 10 tdfn continuous power dissipation (t a = +70 c) (derate 14.9mw/ c above +70 c) (multilayer board) .1188.7mw junction-to-ambient thermal resistance ( ja ) ........... 67.3c/w junction-to-case thermal resistance ( jc ) ................ 18.2c/w 14 tssop continuous power dissipation (t a = +70 c) (derate 25.6mw/ c above +70 c) .......................... 2051.3mw junction-to-ambient thermal resistance ( ja ) .............. 39 c/w junction-to-case thermal resistance ( jc ) ..................... 3 c/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-sw normal switching mode, no load max17502e/f/g 4.75 6.75 ma max17502h 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 ldov 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 downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, 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 = 2.2f, 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 refer - enced 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 max17502e, v fb = 3.3v 6.8 12 17 a max17502f, v fb = 5v 6.8 12 17 max17502g/h, v fb = 0.9v 100 na output voltage (v out ) output voltage range v out max17502e 3.248 3.3 3.352 v max17502f 4.922 5 5.08 max17502g 0.9 0.92 x v in max17502h 0.9 0.965 x v in transconductance amplifier (comp) transconductance g m i comp = 2.5 a, max17502g/h 510 590 650 s comp source current i comp_src max17502g/h 19 32 55 a comp sink current i comp_sink max17502g/h 19 32 55 a current-sense transresistance r cs max17502g/h 0.45 0.5 0.55 v/a downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, 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 = 2.2f, 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 refer - enced to gnd, unless otherwise noted.) (note 2) note 2: all limits are 100% tested at +25c. limits over the operating temperature range and relevant supply voltage range are guaranteed by design and characterization. note 3: guaranteed by design, not production tested. parameter symbol conditions min typ max units current limit peak current-limit threshold i peak-limit 1.4 1.65 1.9 a runaway current-limit threshold i runaway- limit 1.45 1.7 2 a sink current-limit threshold i sink-limit max17502e/f/g/h 0.56 0.65 0.74 a timings switching frequency f sw v fb > v out- hicf max17502e/f/g 560 600 640 khz max17502h 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 max17502e/f/g 92 94 96 % max17502h 96.5 97.5 98.5 lx dead time 5 ns resetreset 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 downloaded from: http:///
maxim integrated 5 www.maximintegrated.com max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter typical operating characteristics (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2f, 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 refer - enced to gnd, unless otherwise noted.) max17502e efficiency vs. load current, 3.3v output, figure 7 circuit load current (ma) efficiency (%) 900 800 600 700 300 400 500 200 60 70 80 90 100 100 1000 v in = 36v v in = 24v v in = 12v max17502 toc01 max17502f efficiency vs. load current, 5v output, figure 8 circuit load current (ma) efficiency (%) 900 800 600 700 300 400 500 200 60 70 80 90 100 50 100 1000 v in = 12v v in = 24v v in = 36v v in = 48v max17502 toc02 max17502e load and line regulation, 3.3v output, figure 7 circuit load current (ma) output voltage (v) 3.285 3.290 3.295 3.300 3.305 3.3103.280 v in = 24v v in = 12v v in = 36v 900 800 700 600 500 400 300 200 100 0 1000 max17502 toc03 max17502f load and line regulation, 5v output, figure 8 circuit load current (ma) output voltage (v) 900 800 600 700 200 300 400 500 100 4.96 4.97 4.98 4.99 5.00 5.01 5.02 5.03 5.04 5.054.95 0 1000 v in = 12v v in = 24v v in = 36v v in = 48v max17502 toc04 shutdown current vs. temperature max17502 toc05 temperature (c) shutdown current (a) 100 120 80 60 40 20 0 -20 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.100.70 -40 no-load switching current vs. temperature max17502 toc06 temperature (c) no-load switching current (ma) 100 120 80 60 40 20 0 -20 4.85 4.90 4.95 5.004.80 -40 en/uvlo threshold vs. temperature max17502 toc07 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 1.231.22 1.21 1.19 1.17 1.15 1.12 -40 rising threshold fa lling threshold output voltage vs. temperature (max17502e), 3.3v output, figure 7 circuit max17502 toc08 temperature (c) output voltage (v) 100 120 80 60 40 20 0 -20 3.275 3.300 3.325 3.3503.250 -40 output voltage vs. temperature (max17502f), 5v output, figure 8 circuit max17502 toc09 temperature (c) output voltage (v) 100 120 80 60 40 20 0 -20 4.975 5.000 5.025 5.0504.950 -40 downloaded from: http:///
maxim integrated 6 www.maximintegrated.com max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2f, 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 refer - enced to gnd, unless otherwise noted.) feedback voltage vs. temperature max17502 toc10 temperature (c) feedback voltage (v) 100 120 80 60 40 20 0 -20 0.89 0.90 0.91 0.920.88 -40 peak and runaway current limit vs. temperature max17502 toc11 temperature (c) current limit (a) 100 120 80 60 40 20 0 -20 1.71.6 1.5 1.8 1.9 2.01.4 -40 peak current limit runa wa y current limit switching frequency vs. temperature max17502 toc12 temperature (c) switching frequency (khz) 100 120 80 60 40 20 0 -20 400300 500 600 700200 -40 soft-start/shutdown from en/uvlo (max17502e), 3.3v output, figure 7 circuit max17502 toc13 1ms/div en/uvlo 2v/div v out 1v/div i out 500ma/div reset 2v/div soft-start/shutdown from en/uvlo (max17502f), 5v output, figure 8 circuit max17502 toc14 1ms/div en/uvlo 2v/div v out 2v/div i out 500ma/div reset 5v/div full-load soft-start from v in (max17502e), 3.3v output, figure 7 circuit max17502 toc15 400s/div v in 20v/div v out 1v/div i out 500ma/div reset 2v/div full-load soft-start from v in (max17502f), 5v output, figure 8 circuit max17502 toc16 400s/div v in 20v/div v out 2v/div i out 500ma/div reset 5v/div downloaded from: http:///
maxim integrated 7 www.maximintegrated.com max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2f, 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 refer - enced to gnd, unless otherwise noted.) soft-start with 2v prebias (max17502e), 3.3v output, figure 7 circuit max17502 toc17 400s/div en/uvlo 2v/div v out 1v/div reset 2v/div soft-start with 2.5v prebias (max17502f), 5v output, figure 8 circuit max17502 toc18 400s/div en/uvlo 2v/div v out 1v/div reset 5v/div load transient response of max17502e (load current stepped from no-load to 500ma), 3.3v output, figure 7 circuit max17502 toc19 40s/div v out (ac) 50mv/div i out 200ma/div load transient response of max17502f (load current stepped from no-load to 500ma), 5v output, figure 8 circuit max17502 toc20 20s/div v out 100mv/div i out 200ma/div load transient response of max17502e (load current stepped from 500ma to 1a), 3.3v output, figure 7 circuit max17502 toc21 20s/div v out (ac) 50mv/div i out 500ma/div load transient response of max17502f (load current stepped from 500ma to 1a), 5v output, figure 8 circuit max17502 toc22 20s/div v out 100mv/div i out 500ma/div downloaded from: http:///
maxim integrated 8 www.maximintegrated.com max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter typical operating characteristics (continued) (v in = 24v, v gnd = v pgnd = 0v, c vin = 2.2f, 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 refer - enced to gnd, unless otherwise noted.) bode plot of max17502e at 1a load, 3.3v output, figure 7 circuit max17502 toc25 f cr = 55.2khz pm = 53 45 67 89 12 bode plot of max17502f at 1a load, 5v output, figure 8 circuit max17502 toc26 f cr = 60.5khz pm = 58 45 67 89 12 switching waveforms of max17502f at 1a load, 5v output, figure 8 circuit max17502 toc23 2s/div v out (ac) 50mv/div i lx 500ma/div lx 20v/div output overload protection of max17502f, 5v output, figure 8 circuit max17502 toc24 20ms/div v out 500mv/div i out 500ma/div downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 9 pin description pin conigurations pin name function tdfn tssop 1 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 3 v in power-supply input. the input supply range is from 4.5v to 60v. 3 4 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 6 v cc 5v ldo output. bypass v cc with 1f ceramic capacitance to gnd. 5 7 fb/vo feedback input. for ixed 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 8 ss soft-start input. connect a capacitor from ss to gnd to set the soft-start time. 7 9 n.c./comp external loop compensation. for adjustable output voltage (max17502g/h), connect to an rc network from comp to gnd. see external loop compensation for adjustable output versions section for more details. for ixed output voltage (max17502e/f), this pin is a no connect (n.c.) and should be left unconnected. 8 10 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 11 gnd analog ground 10 13, 14 lx switching node. connect lx to the switching side of the inductor. lx is high impedance when the device is in shutdown mode. 2, 5, 12 n.c. no connection. not internally connected. 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. 1413 12 11 10 9 8 1 23 45 6 7 lxlx n.c. gnd en/uvlo v in n.c. pgnd top view max17502 reset n.c./comp ss fb /v o v cc n.c. tssop (5mm x 4.4mm) + top view*ep = exposed pad. connect to gnd tdfn (3mm x 2mm) max17502 12 3 4 5 pgnd v in en/uvlo v cc fb /v o lxgnd reset n.c./comp ss + ep* 10 98 7 6 ep* downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 10 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 (for e, f versions) n driver v cc 5a ssreset n.c./comp ss hiccup comp hiccup clk osc pwm compar at or en ss 900mv fb max17502 downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 11 detailed description the max17502 synchronous step-down regulator oper - ates from 4.5v to 60v and delivers up to 1a 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. 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 max17502: overcurrent protection/hiccup mode the device is provided with a robust overcurrent-protec - tion scheme that protects the device under overload and output short-circuit conditions. a cycle-by-cycle peak cur - rent limit turns off the high-side mosfet whenever the high-side switch current exceeds an internal limit of 1.65a (typ). a runaway current limit on the high-side switch cur - rent at 1.7a (typ) protects the device under high input volt - age, short-circuit conditions when there is insufficient out - put 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 71.14% (typ) of its nominal value any time after soft-start is complete, hiccup mode is triggered. 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. part version f sw (max) (khz) d max max17502e/f/g 640 0.92 max17502h 320 0.965 downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 12 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 2.2f 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 2.2f 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, and output voltage determine the inductor value as follows: l = 2.4 x v ou t f sw where v out and f sw are nominal values. 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) = 1.65a 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 output voltage versions, connect a mini - mum of 22f (1210) capacitor at the output. for fixed 5v output voltage versions, connect a minimum of 10f (1210) capacitor at the output. for adjustable output volt - age versions, the output capacitance 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. soft-start capacitor selection the selected output capacitance (c sel ) and the output voltage (v out ) determine the minimum required soft-start capacitor as follows: c ss -6 x c sel x v ou t the soft-start time (t ss ) is related to the capacitor connected at ss (c ss ) by the following equation: 5.55 x 10 -6 c ss t ss = downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 13 figure 1. setting the output voltage figure 2. adjustable en/uvlo network adjusting output voltage the max17502e and max17502f have preset output 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 max17502g/h offer an adjustable output voltage from 0.9v to 92%v in . set the output voltage with a resis - tive voltage-divider connected 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 values of r4 and r5: for max17502g, select the parallel combination of r4 and r5, rp to be less than 15k. for the max17502h, 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 . external loop compensation for adjustable output versions the max17502 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 2 g 1 0.4 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 6000 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 c g c 2 x r = c p can be calculated as follows: = p z sw 1 c r f figure 3. external compensation network r5 r4 fb /v o gnd v out r2 r1 en/uvlo gnd v in r z to comp pin c z c p downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 14 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 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). for a typical multilayer board, the thermal performance metrics for the 10-pin tdfn package are given as: ja 67.3 c w = jc 18.2 c w = for a typical multilayer board, the thermal performance metrics for the 14-pin tssop package are given as: ja 39 c w = jc 3cw = 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 = + 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 max17502 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 , 5 , and 6 show the recommended component placement for max17502 in tdfn and tssop packages. downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 15 figure 4. recommended component placement for max17502e/f ep r4 c2 c1 r2 r1 v in plane pgnd plane gnd plane vias to bottom side pgnd plane vias to bottom side v out track vias to bottom side gnd plane l1 v out plane lx plane c3 reset c4 downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 16 figure 5. recommended component placement for max17502g 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 bottom side pgnd plane vias to bottom side v out track vias to bottom side gnd plane c4 downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 17 figure 6. recommended component placement for max17502h pgnd plane c1 c4 l1 v out plane v in plane lx plane ep c5 c9 c3 gnd plane r5 r4 r1 r2 c2 r3 reset vias to bottom side pgnd plane vias to bottom side v out track vias to bottom side gnd plane downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 18 typical applications circuits figure 7. max17502e application circuit (3.3v output, 1a maximum load current, 600khz switching frequency) figure 8. max17502f application circuit (5v 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 /v o reset v in 24v c1 2.2f 1210 12 ju1 r1 3.32m? r2 866? 3 max17502e reset l1 1 l1lps62313 c422f 1210 v out 3.3v1 c2 1f c3 3300pf n.c. ss v cc en/uvlo v in lx pgnd gnd fb /v o reset v in 24v c1 2.2f 1210 12 ju1 r1 3.32m? r2 866? 3 max17502f reset l1 22 c410f 1210 v out v1 l1lps623223 downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 19 figure 9. max17502g application circuit (12v output, 1a maximum load current, 600khz switching frequency) figure 10. max17502h application circuit (2.5v output, 1a maximum load current, 300khz switching frequency) c2 1f c3 6800pf r3 20k? c5 2200pf c9 12pf comp ss v cc en/uvlo v in lx pgnd gnd fb /v o reset v in 2v c1 22f 1210 12 u1 r1 332m? r2 316k? 3 max17502g reset l1 c10f 1210 v out 12v1 r1k? r5 1k? l1mss10383 c2 1f c3 6800pf r3 16.9k? c5 3300pf c9 47pf comp ss v cc en/uvlo v in lx pgn gn f /v o rese v in 24v c1 2.2f 1210 12 u1 r1 3.32m? r2 1m? 3 max17502h rese l1 22 c4 47f 1210 v ou 2.5v1 r469.8k? r5 39.2k? l1lps6235223 downloaded from: http:///
max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter www.maximintegrated.com maxim integrated 20 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 pad. ordering information/selector guide part pin-package output voltage (v) switching frequency (khz) mode max17502eatb+ 10 tdfn-ep* 3.3 600 pwm max17502fatb+ 10 tdfn-ep* 5 600 pwm max17502gatb+ 10 tdfn-ep* adjustable 600 pwm max17502haud+ 14 tssop-ep* adjustable 300 pwm package type package code outline no. land pattern no. 10 tdfn t1032n+1 21-0429 90-0082 14 tssop u14e+3 21-0108 90-0119 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. ? 2015 maxim integrated products, inc. 21 max17502 60v, 1a, ultra-small, high-eficiency, synchronous step-down dc-dc converter revision history revision number revision date description pages changed 0 5/12 initial release 1 11/12 added max17502g and max17502h to data sheet 1C17 2 1/13 added dotted line for exposed pad in pin coniguration , and added explanation on detailed condition for reset 9, 11 3 8/14 updated general description , beneits and features , pin description , and adjusting output voltage sections. 1, 9, 13 4 6/15 added output voltage to toc captions 8C12, 16C18, 22, 23 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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