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MP2497-A 3a, 50v, 100khz step -down converter with programmable output ovp threshold MP2497-A rev. 1.0 www.monolithicpower.com 1 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. the future of analog ic technology description the MP2497-A is a monolithic step-down switch mode converter with a programmable output current limit. the MP2497-A is the high efficiency version of mp2497. it has fast switching speed thus the switching loss is greatly reduced. it achieves 3a continuous output current over a wide input supply range with excellent load and line regulation. an internal 2-4ms soft start prevents inrush current at turning on. and it is capable of providing output line drop compensation. fault condition protection includes hiccup current limit and short circuit protection, programmable output over voltage protection and thermal shutdown. the MP2497-A requires a minimum number of readily available standard external components. the MP2497-A is available in soic8e package. features ? wide 4.5v to 50v operating input range ? programmable output over voltage protection ? output adjustable from 0.8v to 25v ? 0.15 ? internal power mosfet switch ? internal 4ms soft start ? stable with low esr output ceramic capacitors ? fixed 100khz frequency ? fast switching speed ? thermal shutdown ? output line drop compensation ? hiccup circuit limit and short circuit protection ? available in soic8e package applications ? usb power supplies ? automotive cigarette lighter adapters ? power supply for linear chargers all mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website under products, quality assurance page. ?mps? and ?the future of analog ic technology? are registered trademarks of monolithic power systems, inc. typical application + l1 MP2497-A sw ovp isp isn fb bst vin gnd gnd c 10 gnd vin r 4 r 3 diode c 4 c 3 rsense c 5 r 7 r 5 c 7 10nf c 8 10nf r 1 r 2 c 9 150pf r 6 c 6 c 11 c 1 c 2 vout output current(a) efficiency vs. output current 60 65 70 75 80 85 90 95 0.1 0.5 0.9 1.3 1.7 2.1 2.5 2.9 v in =12v v in =24v v in =50v
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 2 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. ordering information part number package top marking mp2497gn-a * soic8e MP2497-A * for tape & reel, add suffix ?z (e.g. mp2497gn-a?z); package reference soic8e absolute maxi mum ratings (1) input voltage v in .......................................... 60v v isn, v isp .............................................. 0v to 25v |v isn - v isp | ........................................... 0v to 0.4v v sw ........................................ -0.3v to v in + 0.3v v bst ................................................... v sw + 6.5v all other pins ............................... -0.3v to +6.5v junction temperature ............................... 150 ? c lead temperature .................................... 260 ? c storage temperature ............... -65 ? c to +150 ? c continuous power dissipation (t a = +25c) (2) soic8e ...................................................... 2.5w recommended operating conditions (3) input voltage v in .............................. 4.5v to 50v output voltage v out (v in >26.5v) ..... 0.8v to 25v output voltage v out (v in <=26.5v) ...................... ......................................... 0.8v to (v in ?1.5)v operating junction temp. (t j ). -40c to +125c thermal resistance (4) ja jc soic8e .................................. 50 ...... 10 ... ? c/w notes: 1) exceeding these ratings may damage the device. 2) the maximum allowable power dissipation is a function of the maximum junction temperature t j (max), the junction-to- ambient thermal resistance ja , and the ambient temperature t a . the maximum allowable continuous power dissipation at any ambient temperature is calculated by p d (max) = (t j (max)-t a )/ ja . exceeding the maximum allowable powe r dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. internal thermal shutdown circuitry protects the device from permanent damage. 3) the device is not guaranteed to function outside of its operating conditions. 4) measured on jesd51-7, 4-layer pcb.
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 3 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. electrical characteristics v in = 12v, t a = +25 ? c, unless otherwise noted. parameters symbol condition min typ max units feedback voltage v fb t a =+25c 4.5v ? v in ? 50v 0.78 0.8 0.82 v t a =-40c to +85c 4.5v ? ? 50v 0.775 0.8 0.825 feedback bias current i bias(fb) v fb = 0.8v 10 na output over voltage reference v ovref t a =-40 ? c to +85 ? c 1.10 1.23 1.36 v input bias current (ovp) i bias ( ovp ) v ovp =1.23v 0.1 a switch on resistance r ds(on) 0.15 ? current limit (5) duty cycle=10% 5 a oscillator frequency f sw v fb = 0.6v 80 100 120 khz boot-strap voltage v bst - v sw 4.5 v minimum on time (5) t on 100 ns sw rising edge (5) t rise 3 ns sw falling edge (5) t fall 3 ns under voltage lockout threshold rising 2.9 3.4 3.9 v under voltage lockout threshold hysteresis 200 mv load line compensation gain g llc v isp -v isn =100mv, check i fb 15 20 25 a/v current sense voltage v isp ?v isn v isp , v isn 0.5?15v 90 100 110 mv input bias current (isn, isp) i bias ( isn , isp ) v isp , v isn 0.5?15v -1 -0.5 +1 a supply current (quiescent) v ovp = 0v, v fb = 1v 1.2 1.5 ma thermal shutdown (5) 150 c thermal shutdown hysteresis (5) 30 c notes: 5) guaranteed by design.
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 4 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical characteristics c1=220 f, c2=2.2 f, c3=100 f, c4=22 f, l=33 h, r sense =33m ? , t a =25oc unless otherwise noted. output line drop compensation 4.9 4.92 4.94 4.96 4.98 5 5.02 0 connect isp, isn to gnd 0.5 1 1.5 2 2.5 3 3.5 i out (a) i out (a) v out (v) v in =12v v in =24v v in =50v loop gain with phase margin 0.1 1 10 100 1000 frequency(khz) gain (db) phase (degree) efficiency vs. output current load regulation 4.95 4.955 4.96 4.965 4.97 4.975 4.98 4.985 4.99 0 0.5 1 1.5 2 2.5 3 3.5 v out (v) v in =12v v in =24v v in =50v v fb vs. temperature 0.792 0.794 0.796 0.798 0.8 0.802 0.804 -50 -20 10 40 70 100 130 v fb voltage(v) v in =12v v in =12v, v out = 5v, i out =3a resistor load -80 -60 -40 -20 0 20 40 60 80 -200 -150 -100 -50 0 50 100 150 200 gain phase output current(a) 60 65 70 75 80 85 90 95 0.1 0.5 0.9 1.3 1.7 2.1 2.5 2.9 v in =50v v in =36v v in =24v v in =12v v in =8v
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 5 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics (continued) c1=220 f, c2=2.2 f, c3=100 f, c4=22 f, l=33 h, r sense =33m ? , t a =25oc unless otherwise noted.
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 6 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. pin functions package pin # name description 1 vin supply voltage. the MP2497-A operates from a +4.5v to +50v unregulated input. c in is needed to prevent large voltage spikes from appearing at the input. put c in as close to the ic as possible. it is the drain of the internal power device and power supply for the whole chip. 2 gnd, exposed pad ground. this pin is the voltage reference for the regulated output vo ltage. for this reason care must be taken in its layout. this node should be placed outside of the d1 to c in ground path to prevent switching current spikes from inducing voltage noise into the part. connect exposed pad to gnd plane for optimal thermal performance. 3 fb feedback. an external resistor divider from the output to gnd tapped to the fb pin sets the output voltage. to prevent current limit r un away during a short circuit fault condition the frequency-fold-back comparator lowers t he oscillator frequency when the fb voltage is below 250mv. 4 ovp output over voltage protection. connect ovp to the center point of an external resistor divider from output to gnd. the ovp reference is 1.23v. 5 isn negative current sense input. it is used fo r load current limiting and output line drop compensation. 6 isp positive current sense input. it is used for load current limiting and output line drop compensation. 7 bst bootstrap. this capacitor is needed to driv e the power switch?s gate above the supply voltage. it is connected between sw and bst pins to form a floating supply across the power switch driver. an on-chip regulator is used to charge up the external boot-strap capacitor. if the on-chip regulator is not strong enough, one optional diode can be connected from in or out to charge the external boot-strap capacitor. 8 sw switch output. it is the source of power device.
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 7 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. block diagram regulator reference 63m current sense amplifier regulator driver oscillator ramp pwm comparator 72.8pf 2483k 6pf clk errpr amplifier r sense 1.23v ovp comparator hiccup current limit 600mv 10000k 10pf 400k r 1 r 2 200mv in x 6 r s1 r s2 800mv ss circuit 6.2ua figure 1?functional block diagram
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 8 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. operation main control loop the MP2497-A is a current mode buck regulator. that is, the ea output voltage is proportional to the peak inductor current. at the beginning of a cycle sw is off; the error amplifier output voltage is higher than the current sense amplifier output. the rising edge of the 100khz clk signal sets the rs flip-flop. its output turns on sw thus connecting the sw pin and inductor to the input supply. the increasing inductor current is sensed and amplified by the current sense amplifier. ramp compensation is summed to current sense amplifier output and compared to the error amplifier output by the pwm comparator. when the current sense amplifier plus slope compensation signal exceeds the error amplifier output voltage, the rs flip-flop is reset and the MP2497-A reverts to its initial sw off state. if the current sense amplifier plus slope compensation signal does not exceed the comp voltage, then the falling edge of the clk resets the flip-flop. the output of the error amplifier integrates the voltage difference between the feedback and the reference. the polarity is such that an fb pin voltage is lower than 0.8v increases the ea output voltage. since the ea output voltage is proportional to the peak inductor current, an increase in its voltage increases current delivered to the output. an external schottky diode (d1) carries the inductor current when sw is off. hiccup mode current limit protection the output current information for current limit protection is sensed via the isp and isn pins. the sense voltage limit threshold is set at 100mv. MP2497-A has hiccup over current limit function. once the v sense exceeds the 100mv, the current limit loop will turn off high side switch immediately. meanwhile, internal soft start circuit will be reset after fb is lower than 0.3v, and then the high side switch turns on and MP2497-A restarts with a full soft start. this hiccup process is repeated until the fault is removed. and, current limit value can be programmed to be lower by internal current source and external resistors connected to isn and isp pins, when output voltage is lower than 200mv. then, the average short circuit current can be greatly reduced. output over voltage protection the MP2497-A has output over voltage protection. the ovp reference 1.23v is on the positive input of the ovp comparator. the output voltage is fed to ovp pin through an external resistor divider. if the voltage on ovp pin is higher than 1.23v, the high side switch will be turned off immediately and part will be lathed off after a timer delay. output line drop compensation if the trace from MP2497-A output terminator to the load is too long, there will be a voltage drop on the long trace which is variable with load current. MP2497-A is capable of compensating the output voltage drop to keep a constant voltage at load, whatever the load current is. the output voltage is compensated by feeding a current to the top feedback resistance r1. the load line compensation gain can be programmed according to r sense and r trace (figure 2) values.
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 9 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. application information setting the output line drop compensation figure 2 shows the block of output line drop compensation. if the trace to the load is long, there is a voltage drop between v out and v load . v out (voltage at output terminator) is not equal to v load (voltage at load). the voltage drop can be described by: drop out trace vir ?? (1) where, the r trace is the resistance of the output line. ( trace trace1 trace2 rrr ?? ) then, the v load is: load out out trace vvir ??? (2) to keep an accurate and constant load voltage, the output line drop compensation is necessary. MP2497-A offers a compensation method, by adjusting the fb voltage slightly according to the load current. the relation between v out and v fb can be described by: out fb out sense fb vv ir 6 v r1 r2 400k ??? ?? ? (3) where, v fb is 0.8v. then, the v out can be calculated by: out sense out ir 6r1 r1 v(1)0.8v r2 400k ??? ?? ? ? ? (4) the v load is determined by: out sense load out trace ir 6r1 r1 v(1)0.8v r2 400k ir ??? ?? ? ? ? ?? (5) to maintain the v load is not variable with load current. the equation below should be satisfied: out sense out trace ir 6r1 ir 400k ??? ?? ? (6) simplify the formula above, we can get: trace sense r 400k r1 6r ?? ? ? (7) in the formula above, r sense is known. and r trace can be tested or evaluated. so, we can select a proper top feedback resistor r1 according to the r trace and r sense to compensate the output line voltage drop. figure 2?output line drop compensation setting the output voltage the external resistor divider is used to set the output voltage (see the typical application circuit on the front page). the feedback resistor r1 is decided by output line drop compensation. r2 is then given by: 1 v 8 . 0 v 1 r 2 r out ? ? (8)
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 10 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. selecting the inductor a 10h to 47h inductor with a dc current rating of at least 25% percent higher than the maximum load current is recommended for most applications. for highest efficiency, the inductor dc resistance should be less than 200m ? . for most designs, the inductance value can be derived from the following equation. out in out in l osc v(vv) l vif ?? ? ?? ? (9) where i l is the inductor ripple current. choose inductor current ripple to be approximately 30% of the maximum load current, 3a. the maximum inductor peak current is: l l(max) load i ii 2 ? ?? (10) under light load conditions below 100ma, larger inductance is recommended for improving efficiency. selecting the input capacitor the input capacitor reduces the surge current drawn from the input and also the switching noise from the device. the input capacitor impedance at the switching frequency should be less than the input source impedance to prevent high frequency switching current from passing to the input. ceramic capacitors with x5r or x7r dielectrics are highly recommended because of their low esr and small temperature coefficients. for most applications, a 4.7f capacitor is sufficient. selecting the output capacitor the output capacitor keeps output voltage small and ensures regulation loop stability. the output capacitor impedance should be low at the switching frequency. ceramic capacitors with x5r or x7r dielectrics are recommended. setting the output ovp threshold the output ovp threshold is set by connecting an external resistor divider (r3, r4 see the typical application circuit on the front page) at ovp pin. choose r3 to be 39k ? for lower power dissipation. then, r4 is given by: ovp ovref r3 r4 (k ) v 1 v ? ? ? (11) where, v ovref is the ovp reference, 1.23v. v ovp is over voltage protection threshold. setting the current limit the hiccup current limit can be set by the dc resistance (dcr) of the inductor, as shown in figure 3a. for more accurate sensing, use a more accurate sense resistor. in figure 3a, the output current limit is set as: out _ l 100mv i dcr ? (12) where, dcr is the dc resistance of the inductor winding. r a and c a is a low pass filter. in figure 3b, the output current limit is set as: out _ l sense 100mv i r ? (13) figure 3?current sensing methods
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 11 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. programming the short circuit current limit the hiccup current limit at output short condition can be programmed to be lower by external resisters (r s1 , r s2 , r s1 =r s2 ), as shown in figure 4. when output voltage is lower than 200mv, the current limit is described by: out _ sl sense s1 i r 6.2 a r 100mv ????? (14) the current limit at output short condition is: s1 out _ sl sense 100mv 6.2 a r i r ??? ? (15) r sense r s1 r s2 200mv 6.2ua figure 4?short circuit current limit pcb layout guide pcb layout is very important to achieve stable operation. it is highly recommended to duplicate evb layout for optimum performance. if change is necessary, please follow these guidelines and take figure 5 for reference. 1) keep the path of switching current short and minimize the loop area formed by input cap, high-side mosfet and external switching diode. 2) bypass ceramic capacitors are suggested to be put close to the vin pin. 3) ensure all feedback connections are short and direct. place the feedback resistors and compensation components as close to the chip as possible. 4) route sw away from sensitive analog areas such as fb. 5) connect in, sw, and especially gnd respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. isp 1 2 3 4 8 7 6 5 ovp fb gnd vin sw bst isn c11 gnd gnd vin vout l1 r5 + c2 r1 r2 r12 r4 r3 r13 c6 r6 c7 c8 r7 c12 c10 c4 r10 c3 + r8 r11 c9 c5 sw d2 r9 top layer bottom layer figure 5?pcb layout
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 12 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. external bootstrap diode it is recommended that an external bootstrap diode be added when the system has a 5v fixed input or the power supply generates a 5v output. this helps improve the efficiency of the regulator. the bootstrap diode can be a low cost one such as in4148 or bat54. this diode is also recommended for high duty cycle operation (when o u t i n v v >65%) and high output voltage (v out >12v) applications. figure 6?external bootstrap diode design example below is a design example following the application guidelines for the specifications: v in 8 to 50v v out 5v v ovp 6v f sw 100khz i out-l 3a the detailed application schematic is shown in figure 7. the typical performance and circuit waveforms have been shown in the typical performance characteristics section. for more possible applications of this device, please refer to related evaluation board data sheets.
MP2497-A ? 3a, 50v, 100khz step-down converter MP2497-A rev. 1.0 www.monolithicpower.com 13 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. figure 7?detailed application schematic
MP2497-A ? 3a, 50v, 100khz step-down converter notice: the information in this document is subject to change wi thout notice. please contact m ps for current specifications. users should warrant and guarantee that third party intellectual property rights ar e not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. MP2497-A rev. 1.0 www.monolithicpower.com 14 5/30/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. package information soic8e (exposed pad)

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