mp2358 2a, 23v, 370khz step-down converter mp2358 rev. 1.3 www.monolithicpower.com 1 3/23/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. the future of analog ic technology tm tm description the mp2358 is a monolithic step-down switch mode converter with a built-in internal power mosfet. it achieves 2a continuous output current over a wide input supply range with excellent load and line regulation. current mode operation provides fast transient response and eases loop stabilization. fault condition protection in cludes cycle-by-cycle current limiting and thermal shutdown. in shutdown mode the regulator draws 23a of supply current. programmable soft-start minimizes the inrush supply current and the output overshoot at initial startup. the mp2358 requires a minimum number of readily available standard external components. evaluation board reference board number dimensions ev2358ds-00a 2.3? x 1.4? x 0.5? EV2358DQ-00A 2.0? x 1.3? x 0.4? features ? 2a output current with qfn package ? 0.18 ? internal power mosfet switch ? stable with low esr output ceramic capacitors ? 93% efficiency ? 23a shutdown mode ? fixed 370khz frequency ? thermal shutdown ? cycle-by-cycle over current protection ? wide 4.75v to 23v operating input range ? output adjustable from 0.92v to 16v ? programmable under voltage lockout ? available in qfn10 (3mm x 3mm) and so8 packages applications ? distributed power systems ? battery charger ? pre-regulator for linear regulators ?mps? and ?the future of analog ic technology? are trademarks of monolithic power systems, inc. typical application mp2358 sw in bs fb ss comp gnd en v out 3.3v/2a input 4.75v - 23v mp2358_tac_s01 open = automatic startup c5 10nf c3 3.9nf c4 10nf d1 b220a c6 open efficiency (%) 95 90 85 80 75 70 65 60 output current (a) mp2358_ec01 efficiency vs output current 0 1.0 0.5 1.5 2.0 2.5 5.0v 3.3v 2.5v
mp2358 ? 2a, 23v, 370khz step-down converter mp2358 rev. 1.3 www.monolithicpower.com 2 3/23/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm package reference mp2358_pd01-qfn10 top view nc bs nc in sw 1 2 3 4 5 ss en comp fb gnd 10 9 8 7 6 exposed pad on backside part number* package temperature mp2358dq qfn10 (3mm x 3mm) ?40 c to +85 c * for tape & reel, add suffix ?z (eg. mp2358dq?z) for lead free, add suffix ?lf (eg. mp2358dq?lf?z) bs in sw gnd ss en comp fb 1 2 3 4 8 7 6 5 top view mp2358_pd02_soic8 part number** package temperature mp2358ds soic8 ?40 c to +85 c ** for tape & reel, add suffix ?z (eg. mp2358ds?z) for lead free, add suffix ?lf (eg. mp2358ds?lf?z) absolute maxi mum ratings (1) supply voltage (v in )..................................... 25v switch node voltage (v sw ) .......................... 26v bootstrap voltage (v bs ) ....................... v sw + 6v feedback voltage (v fb ) .................?0.3v to +6v enable/uvlo voltage (v en )...........?0.3v to +6v comp voltage (v comp ) ...................?0.3v to +6v ss voltage (v ss ) ............................?0.3v to +6v junction temperature ............................ +150 c lead temperature ................................. +260 c storage temperature.............. ?65c to +150 c recommended operating conditions (2) supply voltage (v in ) ...................... 4.75v to 23v operating temperature.................?40 c to +85 c thermal resistance (3) ja jc qfn10 (3x3)........................... 50 ...... 12... c/w soic8.................................... 105 ..... 50... c/w notes: 1) exceeding these ratings may damage the device. 2) the device is not guaranteed to function outside of its operating conditions. 3) measured on approximately 1? square of 1 oz copper. electrical characteristics v in = 12v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units feedback voltage v fb 4.75v v in 23v 0.892 0.920 0.948 v upper switch on resistance r ds(on)1 0.18 ? lower switch on resistance r ds(on)2 10 ? upper switch leakage v en = 0v, v sw = 0v 0 10 a current limit (4) 2.8 3.4 a current sense transconductance output current to comp pin voltage g cs 1.95 a/v error amplifier voltage gain a vea 400 v/v error amplifier transconductance g ea ? i c = 10a 550 830 1150 a/v oscillator frequency f s 370 khz short circuit frequency v fb = 0v 240 khz soft-start pin equivalent output resistance 9 k ?
mp2358 ? 2a, 23v, 370khz step-down converter mp2358 rev. 1.3 www.monolithicpower.com 3 3/23/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm electrical characteristics (continued) v in = 12v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units maximum duty cycle d max v fb = 0.8v 90 % minimum on time t on 100 ns en shutdown threshold i cc > 100a 0.7 1.0 1.3 v enable pull up current v en = 0v 1.0 a en uvlo threshold rising v en rising 2.37 2.50 2.62 v en uvlo threshold hysteresis 210 mv supply current (shutdown) v en 0.4v 23 36 a supply current (quiescent) v en 3v 1.1 1.3 ma thermal shutdown 160 c note: 4) slope compensation changes current limit above 40% duty cycle. pin functions qfn10 pin # soic8 pin # name description 1 nc no connect. 2 1 bs bootstrap. this capacitor (c5) is neede d to drive the power switch?s gate above the supply voltage. it is connected between the sw and bs pins to form a floating supply across the power switch driver. the volta ge across c5 is about 5v and is supplied by the internal +5v supply when the sw pin voltage is low. 3 nc no connect. 4 2 in supply voltage. the mp2358 operates fr om a +4.75v to +23v unregulated input. c1 is needed to prevent large voltage spikes from appearing at the input. 5 3 sw switch. this connects the inductor to either in through m1 or to gnd through m2. 6 4 gnd ground. this pin is the voltage refere nce for the regulated output voltage. for this reason care must be taken in its layout. th is node should be placed outside of the d1 to c1 ground path to prevent switching current spikes from inducing voltage noise into the part. 7 5 fb feedback. an external resistor divider from the output to gnd, tapped to the fb pin, sets the output voltage. to prevent current limit runaway during a short circuit fault condition the frequency foldback comparator lowers the oscillator frequency when the fb voltage is below 400mv. 8 6 comp compensation. this node is the output of the transconductance erro r amplifier and the input to the current comparator. frequency compensation is done at this node by connecting a series r-c to ground. see the compensation section for exact details. 9 7 en enable/uvlo. a voltage greater than 2.62v enables operation. leave en unconnected if unused. an under voltage lockout (uvlo) function can be implemented by the addition of a resistor divider from v in to gnd. for complete low current shutdown the en pin voltage needs to be less than 700mv. 10 8 ss soft-start. connect ss to an external capacitor to program the soft-start. if unused, leave it open.
mp2358 ? 2a, 23v, 370khz step-down converter mp2358 rev. 1.3 www.monolithicpower.com 4 3/23/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm typical performanc e characteristics v in = 12v, v out = 3.3v, t a = +25 c, unless otherwise noted. v in ac 500mv/div. v out ac 50mv/div. v sw 10v/div. i l 2a/div. mp2358-tpc01 steady state i out = 2a v en 10v/div. v out 2v/div. v sw 10v/div. i l 1a/div. v en 10v/div. v out 2v/div. v sw 10v/div. i l 1a/div. 4ms/div. mp2358-tpc02 startup no load 4ms/div. mp2358-tpc03 startup 1a load v en 10v/div. v out 2v/div. v sw 10v/div. i l 1a/div. startup 2a load 4ms/div. mp2358-tpc04 v out ac 500mv/div. i l 1a/div. i out 1a/div. mp2358-tpc05
mp2358 ? 2a, 23v, 370khz step-down converter mp2358 rev. 1.3 www.monolithicpower.com 5 3/23/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm operation the mp2358 is a current mode regulator. that is, the comp pin voltage is proportional to the peak inductor current. at the beginning of a cycle: the upper transistor m1 is off; the lower transistor m2 is on (see figure 1); the comp pin voltage is higher than the current sense amplifier output; and the current comparator?s output is low. the rising edge of the 370khz clk signal sets the rs flip-flop. its output turns off m2 and turns on m1 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 current comparator. when the current sense amplifier plus slope compensation signal exceeds the comp pin voltage, the rs flip-flop is reset and the mp2358 reverts to its initial m1 off, m2 on 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 0.92v bandgap reference. the polarity is such that a fb pin voltage lower than 0.92v increases the comp pin voltage. since the comp pin voltage is proportional to the peak inductor current an increase in its voltage increases current delivered to the output. the lower 10 ? switch ensures that the bootstrap capacitor voltage is charged during light load conditions. external schottky di ode d1 carries the inductor current when m1 is off. mp2358_bd01 lockout comparator error amplifier frequency foldback comparator internal regulators 1.8v slope comp clk current comparator current sense amplifier shutdown comparator comp in en gnd oscillator 240khz/ 370khz s r q sw bs 5v + q 1.0v + + 2.50v/ 2.29v + 0.92v 0.4v + + fb -- -- -- -- -- -- ss figure 1?functional block diagram
mp2358 ? 2a, 23v, 370khz step-down converter mp2358 rev. 1.3 www.monolithicpower.com 6 3/23/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm application information component selection setting the output voltage the output voltage is set using a resistive voltage divider from the output voltage to fb pin. the voltage divider divides the output voltage down to the feedback voltage by the ratio: 2 r 1 r 2 r v v out fb + = where v fb is the feedback voltage and v out is the output voltage. thus the output voltage is: 2 r 2 r 1 r 92 . 0 v out + = a typical value for r2 can be as high as 100k ? , but a typical value is 10k ? . using that value, r1 is determined by: ) 92 . 0 v ( 87 . 10 1 r out ? = for example, for a 3.3v output voltage, r2 is 10k ? , and r1 is 25.8k ? . inductor the inductor is required to supply constant current to the output load while being driven by the switched input voltage. a larger value inductor will result in less ripple current that will result in lower output ripple voltage. however, the larger value inductor will have a larger physical size, higher series resistance, and/or lower saturation current. a good rule for determining the inductance to use is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum switch current limit. also, make sure that the peak inductor current is below the maximum switch current limit. the inductance value can be calculated by: ? ? ? ? ? ? ? ? ? = in out l s out v v 1 ? i f v l where f s is the switching frequency, ? i l is the peak-to-peak inductor ripple current and v in is the input voltage. choose an inductor that will not saturate under the maximum inductor peak current. the peak inductor current can be calculated by: ? ? ? ? ? ? ? ? ? + = in out s out load lp v v 1 l f 2 v i i where i load is the load current. output rectifier diode the output rectifier diode supplies the current to the inductor when the high-side switch is off. to reduce losses due to the diode forward voltage and recovery times, use a schottky diode. choose a diode whose maximum reverse voltage rating is greater than the maximum input voltage, and whose current rating is greater than the maximum load current. input capacitor the input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the ac current to the step-down converter while maintaining the dc input voltage. use low esr capacitors for the best performance. ceramic capacitors are preferred, but tantalum or low-esr electrolytic capacitors may also suffice. since the input capacitor absorbs the input switching current it requires an adequate ripple current rating. the rms current in the input capacitor can be estimated by: ? ? ? ? ? ? ? ? ? = in out in out load 2 c v v 1 v v i i the worst-case condition occurs at v in = 2v out , where: 2 i i load 2 c = for simplification, choose the input capacitor whose rms current rating greater than half of the maximum load current.
mp2358 ? 2a, 23v, 370khz step-down converter mp2358 rev. 1.3 www.monolithicpower.com 7 3/23/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm the input capacitor can be electrolytic, tantalum or ceramic. when using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor, i.e. 0.1f, should be placed as close to the ic as possible. when using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive volt age ripple at input. the input voltage ripple caused by capacitance can be estimated by: ? ? ? ? ? ? ? ? ? = ? in out in out s load in v v 1 v v 1 c f i v where c1 is the input capacitance value. output capacitor the output capacitor is required to maintain the dc output voltage. ceramic, tantalum, or low esr electrolytic capacitors are recommended. low esr capacitors are preferred to keep the output voltage ripple low. the output voltage ripple can be estimated by: ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? ? = ? 2 c f 8 1 r v v 1 l f v v s esr in out s out out where l is the inductor value, r esr is the equivalent series resist ance (esr) value of the output capacitor and c2 is the output capacitance value. in the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. the output voltage ripple is mainly caused by the capacitance. for simplification, the output voltage ripple can be estimated by: ? ? ? ? ? ? ? ? ? = in out 2 s out out v v 1 2 c l f 8 v ? v in the case of tantalum or electrolytic capacitors, the esr dominates the impedance at the switching frequency. for simplification, the output ripple can be approximated to: esr in out s out out r v v 1 l f v ? v ? ? ? ? ? ? ? = the characteristics of the output capacitor also affect the stability of the regulation system. the mp2358 can be optimized for a wide range of capacitance and esr values. compensation components the mp2358 employs current mode control for easy compensation and fast transient response. the system stability and transient response are controlled through the comp pin. comp pin is the output of the internal transconductance error amplifier. a series capacitor-resistor combination sets a pole-zero combination to control the characteristics of the control system. the dc gain of the voltage feedback loop is given by: out fb vea cs load vdc v v a g r a = where r load is the load resistor value, g cs is the current sense transconductance and a vea is the error amplifier voltage gain. the system has two poles of importance. one is due to the compensation capacitor (c3) and the output resistor of error amplifier, and the other is due to the output capacitor and the load resistor. these poles are located at: vea ea 1 p a 3 c 2 g f = load 2 p r 2 c 2 1 f = where g ea is the error amplifier transconductance. the system has one zero of importance, due to the compensation capacitor (c3) and the compensation resistor (r3). this zero is located at: 3 r 3 c 2 1 f 1 z = the system may have another zero of importance, if the output capacitor has a large capacitance and/or a high esr value. the zero, due to the esr and capacitance of the output capacitor, is located at: esr esr r 2 c 2 1 f =
mp2358 ? 2a, 23v, 370khz step-down converter mp2358 rev. 1.3 www.monolithicpower.com 8 3/23/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm in this case, a third pole set by the compensation capacitor (c6) and the compensation resistor (r3) is used to compensate the effect of the esr zero on the loop gain. this pole is located at: 3 r 6 c 2 1 f 3 p = the goal of compensation design is to shape the converter transfer function to get a desired loop gain. the system crossover frequency where the feedback loop has the unity gain is important. lower crossover frequencies result in slower line and load transient responses, while higher crossover frequencies could cause the system to become unstable. a good rule of thumb is to set the crossover frequency to below one-tenth of the switching frequency. to optimize the compensation components, the following procedure can be used: 1. choose the compensation resistor (r3) to set the desired crossover frequency. determine the r3 value by the following equation: fb out cs ea c v v g g f 2 c 2 3 r = where f c is the desired crossover frequency, which is typically less than one tenth of the switching frequency. 2. choose the compensation capacitor (c3) to achieve the desired phase margin. for applications with typical inductor values, setting the compensation zero, f z1 , to below one forth of the crossover frequency provides sufficient phase margin. determine the c3 value by the following equation: c f 3 r 2 3 c > where r3 is the compensation resistor value. 3. determine if the second compensation capacitor (c6) is required. it is required if the esr zero of the output capacitor is located at less than half of the switching frequency, or the following relationship is valid: 2 f r 2 c 2 1 s esr < if this is the case, then add the second compensation capacitor (c6) to set the pole f p3 at the location of the esr zero. determine the c6 value by the equation: 3 r r 2 c 6 c esr = external bootstrap diode it is recommended that an external boost 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 mp2358 regulator. the bootstrap diode can be a low cost one such as in4148 or bat54. mp2358 sw bs 10nf 5v mp2358_f02 figure 2?external bootstrap diode this diode is also recommended for high duty cycle operation (when in out v v >65%) and high output voltage (v out >12v) applications.
mp2358 ? 2a, 23v, 370khz step-down converter notice: the information in this document is subject to change wi thout notice. please contact mps for current specifications. users should warrant and guarantee that th ird party intellectual property rights are not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp2358 rev. 1.3 www.monolithicpower.com 9 3/23/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm package information qfn10 (3mm x 3mm) 2.95 3.05 2.95 3.05 qfn 10l (3 x 3mm) top view pin 1 identif ication 0.85 0.95 0.000- 0.050 0.178 0.228 side vie w note: 1) dimensions are in millimeters. pin 1 identif ication r0.200 ty p 2.000 ref 2.35 2.45 exp. dap 1.65 1.75 exp. dap 0.500 bsc 0.20 0.30 0.35 0.45 bottom vie w 10 65 1 soic8 note: 1) control dimension is in inches. dimension in bracket is m illimeters. 0.016(0.410) 0.050(1.270) 0 o -8 o detail "a" 0.011(0.280) 0.020(0.508) x 45 o see detail "a" 0.0075(0.191) 0.0098(0.249) 0.229(5.820) 0.244(6.200) seating plane 0.001(0.030) 0.004(0.101) 0.189(4.800) 0.197(5.004) 0.053(1.350) 0.068(1.730) 0.049(1.250) 0.060(1.524) 0.150(3.810) 0.157(4.000) pin 1 ident. 0.050(1.270)bsc 0.013(0.330) 0.020(0.508)
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