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e u p 3476 ds 3 476 ver 1.6 may 2012 1 3a, 28v, 500khz synchronous step-down converter description the eup3476 is a 500khz fixed frequency synchronous current mode buck regulator. the device integrates both 135m high-side switch and 90m low-side switch that provide 3a of continuous load current over a wide operating input voltage of 4.5v to 28v.the internal synchronous power switch increases efficiency and eliminates the need for an external schottky diode. current mode control provides fast transient response and cycle-by-cycle current limit. the eup3476 features short circuit and thermal protection circuits to increase system reliability. externally programmable soft-start allows for proper power on sequencing with respect to other power supllies and avoids input inrush current during startup. in shutdown mode, the supply current drops below 1 a. the eup3476 is available in sop-8 package with the exposed pad. features 3a continuous output current 110ns minimum on time integrated 135m high side switch integrated 90m low side switch wide 4.5v to 28v operating input range output adjustable from 0.8v to 24v up to 95% efficiency programmable soft-start <1 a shutdown current available in 500khz fixed switching frequency thermal shutdown and over current protection input under voltage lockout available in sop-8 (ep) package rohs compliant and 100% lead (pb)-free halogen-free applications distributed power systems networking systems fpga, dsp, asic power supplies typical application circuit figure 1. v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 2 typical application circuit (continued) figur e 2. eup3476 typical application circuit with electrolytic capacitors block di agram figure 3. eup3476 functional block diagram n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 3 pin configurations package type pin co nfigurations sop-8 (ep) pin description number pin name description 1 bs high-side gate drive boost input. bs supplies the drive for the high-side n-channel dmos switch. connect a 0.01f or greater capacitor from sw to bs to power the high side switch. 2 in power input. in supplies the power to the ic, as well as the step-down converter switches. drive in with a 4.5v to 28v power source. bypass in to gnd with a suitably large capacitor to eliminate noise on the input to the ic. see input capacitor . 3 sw power switching output. sw is the switching node that supplies power to the output. connect the output lc filter from sw to the output load. note that a capacitor is required from sw to bs to power the high-side switch. 4 9 (exposed pad) gnd ground. the exposed pad must be soldered to a large pcb and connected to gnd for maximum power dissipation. 5 fb feedback input. fb senses the output voltage and regulates it. drive fb with a resistive voltage divider connected to it from the output voltage. the feedback threshold is 0.8v. see setting the output voltage . 6 comp compensation node. comp is used to compensate the regulation control loop. connect a series rc network from comp to gnd. in some cases, an additional capacitor from comp to gnd is required. see compensation components . 7 en enable input. en is a digital input that turns the regulator on or off. drive en high to turn on the regulator; low to turn it off. connect to in with a 100k pull up resistor for automatic startup. 8 ss soft-start control input. ss controls the soft-start period. connect a capacitor from ss to gnd to set the external soft-start period, or leave ss floating to set the internal soft-start period. a 0.1 f capacitor sets the soft-start period to about 15ms. leave ss pin floating, the internal soft-start period is about 300 s. n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 4 ordering information order number package type markin g operating temperature range EUP3476DIR1 sop-8 (ep) xxxxx p3476 -40 c to +85c eup3476 lead free code 1: lead free, halogen free packing r: tape & reel operating temperature range i: in d ustry standard package type d: sop n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 5 absolute maximum ratings (1) supply voltage (v in ) -------------------------------------------------------- -0.3v to +30v en voltage (v en ) -------------------------------------------------------- -0.3v to +6v switch voltages (v sw ) ------------------------------------------------------ -1v to v in +0.3v bootstrap voltage (v bs ) -------------------------------------------- v sw -0.3v to v sw +6v all other pins ---------------------------------------------------------------------- -0.3v to +6v junction temperature -------------------------------------------------------------------- 150c lead temperature ------------------------------------------------------------------------ 260c storage temperature -------------------------------------------------------- -65c to 150c output voltage v out ----------------------------------------------------------- 0.9v to 26v thermal resistance ja (sop-8_ep) ------------------------------------------------------------------------- 60c /w esd ratings human body mode --------------------------------------------------------------------------- 2kv recommend operating conditions (2) input voltage (v in ) --------------------------------------------------------------- 4.5v to 28v operating temperature range ----------------------------------------------- -40c to +85c note (1): stress beyond those listed under absolute maximum ratings may damage the device. note ( 2): the device is not guaranteed to function outside the recommended operating conditions. electrical characteristics unless otherwise specified, v in =12v ,t a =+25c. eup347 6 symbol parameter conditions min typ max. unit i shut shutdown supply current v en =0v 0.1 3 a i q supply current v en =2v, v comp =0.35v 1.1 1.5 ma v fb feedback voltage 4.5v Qv in Q 28 v 0.784 0.800 0.816 v a ea error amplifier voltage gain 400 v/v g ea error amplifier transconductance i c = 10a 400 a/v r ds(on) 1 high-side switch on-resistance i sw =300ma 135 r ds(on) 2 low-side switch on-resistance i sw =300ma 90 m i leakage high-side switch leakage current v en =0v, v sw =0v 0 10 a i limit upper switch current limit minimu m duty cycle 3.6 4.8 i neg low-side switch reverse current limit from drain to source -1 a g cs comp to current sense transconductance 5.6 a/v f osc1 oscillation frequency v fb =0.76v 400 50 0 600 khz f osc2 short circuit oscillation frequency v fb =0v 100 khz d max maximum duty cycle v fb =0.76v 90 % t on minimum on time 110 ns v en en shutdown threshold voltage v en rising 1.1 1. 5 2 v ehhys en shu tdown threshold voltage hysterisis 0.2 v uvlo input under voltage lockout threshold v in rising 3.8 4. 0 4.2 v uvlohys input under voltage lockout threshold hysteresis 0.2 v i ss soft-start current v ss =0v 6 a t ss soft-start period c ss =0.1f 15 m s t sd thermal shutdown 160 t sdhys thermal shutdown hysteresis 20 c n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 6 typical operating characteristics (c in =10f, c out =22f, l=6.8h, c ss =0.1f ,t a =+25c, unless otherwise noted.) n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 7 typical operating characteristics (continued) (c in =10f, c out =22f, l=6.8h, c ss =0.1f ,t a =+25c, unless otherwise noted.) output ri pple output ripple n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 8 typical operating characteristics (continued) (c in =10f, c out =22f, l=6.8h, c ss =0.1f ,t a =+25c, unless otherwise noted.) external soft-start external soft-start interna l soft-start (without c ss capacitor) internal soft-start (without c ss capacitor) shut down shut down n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 9 typical operating characteristics (continued) (c in =10f, c out =22f, l=6.8h, c ss =0.1f ,t a =+25c, unless otherwise noted.) load transient response short ci rcuit short circuit recovery n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 10 application information setting the output voltage the ou tput voltage is set using a resistive voltage divider connected from the output voltage to v fb . the voltage divide r divides the output voltage down to the feedback voltage by the ratio: 21 2 out fb rr r vv + = thus th e output voltage is: 2 21 out r rr v8.0v + = r 2 can be as high as 100k , but a typical value is 10k . using the typical value for r 2 , r 1 is determined by: k5.12)v8.0v(r out 1 - = for example, for a 3.3v output voltage, r 2 is 10k and r 1 is 31 .25k . induct or the inductor is required to supply constant current to the load while being driven by the switched input voltage. a larger value inductor will result in less ripple current that will in turn results 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 inductance is to allow the peak-to-peak ripple current 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: ) v v 1( if v l in out ls out - d = where v out is the output voltage, v in is the input voltag e, f s is the switching frequency, and ?i l is th e peak-t o-peak inductor ripple current. choose an inductor that will not saturate under the maximum inductor peak current, calculated by: ) v v 1( lf2 v ii in out s out lo ad lp - += wher e i load is the load current. the ch oice of which style inductor to use mainly depends on the price vs. size requirements and any emi constraints. optional schottky diode during the transition between the high-side switch and low-side switch, the body diode of the low-side power mosfet conducts the inductor current. the forward voltage of this body diode is high. an optional schottky diode may be paralleled between the sw pin and gnd pin to improve overall efficiency. input capacitor the input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the ac current 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 will also suffice. choose x5r or x7r dielectrics when using ceramic capacitors. since the input capacitor (c in ) absorbs the input switch i ng current, it requires an adequate ripple current rating. the rms current in the input capacitor can be estimated by: ) v v 1( v v ii in out in out load cin - = the wo rst-case condition occurs at v in = 2v out , where ic in = i l oad /2. for simplification, use an input capacitor with a rms current rating greater than half of the maximum load current. 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 voltage ripple at input. the input voltage ripple for low esr capacitors can be estimated by: ) v v 1( v v fc i v in ut o in ut o sin oad l in - =d where c in is the input capacitor value. for simplification, choose the input capacitor whose rms current rating greater than half of the maximum load current. output capacitor the output capacitor (c out ) is required to maintain the dc out put 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: where c out is the output capacitance value and r esr is the eq uivalent series resistance (esr) value of the output capacitor. when using ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance which is the main cause for the output voltage ripple. for simplification, the output voltage ripple can be estimated by: ) v v 1( clf8 v v in out out 2 s o u t out - =d ) cf8 1 r() v v 1( lf v v out s esr in out s ou t out +- =d n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 11 when using 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( lf v v - =d th e ch aracteristics of the output capacitor also affect the stability of the regulation system. the eup3476 can be optimized for a wide range of capacitance and esr values. compensation components eup3476 employs current mode control for easy compensation and fast transient response. the system stability and transient response are controlled through the comp pin. comp is the output of the internal transconductance error amplifier. a series capacitor-resistor combination sets a pole-zero combination to govern 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 agra = where v fb is the feedback voltage (0.8v), a vea is the error amplifier voltage gain, g cs is the current sense transco nductance and r load is the load resistor value. the syst em has two poles of importance. one is due to the compensation capacitor (c c ) and the output resistor of the error amplifier, and the other is due to the output capacitor and the load resistor. these poles are located at: vea c ea 1p ac2 g f p = load out 2p rc2 1 f p = where g ea is the error amplifier transconductance. the syst em has one zero of importance, due to the compensation capacitor (c c ) and the compensation resistor (r c ). this zero is located at: cc 1z rc2 1 f p = the syst em 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 out esr rc2 1 f p = in thi s case, a third pole set by the compensation capacitor (c 2 ) and the compensation resistor (r c ) is used to com pensate the effect of the esr zero on the loop gain. this pole is located at: 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 instability. a good standard is to set the crossover frequency below one-tenth of the switching frequency. to optimize the compensation components, the following procedure can be used: 1. choose the compensation resistor (r c ) to set the desire d crossover frequency. determine r c by the follo w ing equation: where f c is the desired crossover frequency, which is typica lly below one tenth of the switching frequency. 2. choose the compensation capacitor (c c ) to achieve the de sired phase margin. for applications with typical inductor values, setting the compensation zero (f z1 ) below one-forth of the crossover frequency provid es sufficient phase margin. determine c c by the fo llowing equation: cc c fr2 4 c p > where r c is the compensation resistor. 3. det ermine if the second compensation capacitor (c 2 ) is requ ired. 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 rc2 1 s esr out < p i f t hi s is the case, then add the second compensation capacitor (c 2 ) to set the pole f p3 at the location of the esr ze ro. determine c 2 by the equation: c esr out 2 r rc c = table 1. recommended component selection 4.5v v in < 15v v out (v) r 1 (k ) r 2 (k ) r c (k ) c c (nf) c out ( f) l( h) 1.2 5 10 5 2.2 22 3 1.5 8.75 10 5 2.2 22 3 1.8 12.5 10 8 2.2 22 4.7 2.5 21.25 10 10 2.2 22 4.7 3.3 31.25 10 10 2.2 22 6.8 5 52.5 10 15 2.2 22 6.8 8 90 10 20 2.2 22 6.8 10 115 10 20 2.2 22 6.8 fb out cs ea s out fb out cs ea c out c v v gg f1.0c 2 v v gg fc2 r p < p = c2 3p rc2 1 f p = n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 12 table 2. recommended component selection 15 v in 28v v out (v) r 1 (k ) r 2 (k ) r c (k ) c c (nf) c 2 (pf) c out ( f) l( h) 1.2 5 10 5 2.2 20 22 3 1.5 8.75 10 5 2.2 20 22 3 1.8 12.5 10 8 2.2 20 22 4.7 2.5 21.25 10 10 2.2 20 22 4.7 3.3 31.25 10 10 2.2 20 22 6.8 5 52.5 10 15 2.2 20 22 6.8 8 90 10 20 2.2 20 22 6.8 10 115 10 20 2.2 20 22 6.8 n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com
eup3476 ds3476 ver 1.6 may 2012 13 packaging information sop-8 (ep) remark: exposed pad outline drawing is for reference only. millimeters inches symbols min. normal max. min. normal max. a 1.35 - 1.75 0.053 - 0.069 a1 0.00 - 0.25 0.000 - 0.010 d 4.80 4.90 5.00 0.189 0.193 0.197 e1 3.70 3.90 4.00 0.146 0.154 0.157 d1 1.65 2.00 2.35 0.065 0.079 0.093 e2 1.65 2.00 2.35 0.065 0.079 0.093 e 5.80 6.00 6.20 0.228 0.236 0.244 l 0.40 - 1.27 0.016 - 0.050 b 0.31 - 0.51 0.012 - 0.020 e 1.27 0.050 n~n?t?m?w3^v?mw`r?y?b?g ?pqls? tel: 0755-8398 3377 / 135 9011 2223 http://www.gofotech.com v?mw`r?y?b? www.gofotech.com

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