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semiconductors description the zxsc410 is voltage mode boost converter in sot23-6 package. its excellent load and line regulation means that for the full supply range from lithium ion cells, the output voltage will typically change by less than 1%. using high efficiency zetex switching transistors allow output voltages of tens of volts depending on the selected transistor. the zxsc420 includes a battery low indicator. this operates by indicating when the converter is no longer able to maintain the regulated output voltage rather than setting a preset threshold, thereby making it suitable for various battery options and load currents. features ? 1.65v to 8v supply range ? typical output regulation of 1% ? over 85% typical efficiency ? output currents up to 300ma ? 4.5 a typical shutdown current zxsc410 ? end of regulation output zxsc420 applications ? system power for battery portable products ? lcd bias ? local voltage conversion device marking ? c410 zxsc410 ? c420 zxsc420 zxsc410 zxsc420 issue 2 - may 2003 1 voltage mode boost converter device reel size tape width quantity per reel zxsc410e6ta 7? 8mm 3000 units zxsc420e6ta 7? 8mm 3000 units ordering information s o t 2 3 - 6 v cc gnd sense drive stdn v fb u1 zxsc410 q1 fmmt617 c2 d1 zhcs1000 l1 c1 r2 r3 r1 v in v out typical applications diagram
absolute maximum ratings v cc -0.3v to +10v drive -0.3v to v cc + 0.3v eor -0.3v to v cc + 0.3v * (zxsc420 only) stdn -0.3v to the lower of (+5.0v) or (v cc + 0.3v) * (zxsc410 only) v fb , sense -0.3v to the lower of (+5.0v) or (v cc + 0.3v) operating temp. -40 c to +85 c storage temp. -55 c to +125 c power dissipation 450mw zxsc410 zxsc420 semiconductors issue 2 - may 2003 2 symbol parameter conditions limits units min typ max supply parameters v cc v cc range 1.8 8 v iq 1 quiescent current v cc = 8v 220 a i stdn shutdown current 4.5 a eff 2 efficiency 50ma > i out > 300ma 85 % acc ref reference tolerance 1.8v < v cc < 8v -3.0 3.0 % tco ref reference temp co 0.005 %/ c t drv discharge pulse width 1.8v < v cc < 8v 1.7 s f osc operating frequency 200 khz input parameters v sense sense voltage 22 28 34 mv i sense sense input current v fb =0v;v sense =0v -1 -7 -15 a v fb feedback voltage t a =25 c 291 300 309 mv i fb 2 feedback input current v fb =0v;v sense =0v -1.2 -4.5 a v ih shutdown high voltage 1.5 1 v cc v v il shutdown low voltage 0 0.55 v dv ln line voltage regulation 0.5 %/v output parameters i out 3 output current v in >2v,v out =v in 300 ma i drive transistor drive current v drive = 0.7v 2 3.4 5 ma v drive transistor voltage drive 1.8v < v cc <8v 0 v cc -0.4 v c drive mosfet gate drive cpbty 300 pf voh eor eor flag output high i eor = -300na 2.5 v cc v vol eor eor flag output low i eor = 1ma 0 1.15 v t eor eor delay time t a =25 c 70 195 250 s di ld load current regulation 0.01 %ma electrical characteristics test conditions v cc = 3v, t= -40 c to 85 c unless otherwise stated. note 1 excluding gate/base drive current. 2 i fb is typically half of these values at 3v 3 system not device spec, including recommended transistors.
typical characteristics zxsc410 zxsc420 semiconductors issue 2 - may 2003 3
device description bandgap reference all threshold voltages and internal currents are derived from a temperature compensated bandgap reference circuit with a reference voltage of 1.22v nominal. dynamic drive output depending on the input signal, the output is either ? low ? or ? high ? . in the high state a 2.5ma current source (max drive voltage = vcc-0.4v) drives the base or gate of the external transistor. in order to operate the external switching transistor at optimum efficiency, both output states are initiated with a short transient current in order to quickly discharge the base or the gate of the switching transistor. switching circuit the switching circuit consists of two comparators, comp1 and comp2, a gate u1, a monostable and the drive output. normally the drive output is ? high ? ; the external switching transistor is turned on. current ramps up in the inductor, the switching transistor and external current sensing resistor. this voltage is sensed by comparator, comp2, at input i sense . once the current sense voltage across the sensing resistor exceeds 20mv, comparator comp2 through gate u1 triggers a re-triggerable monostable and turns off the output drive stage for 2s. the inductor discharges to the load of the application. after 2s a new charge cycle begins, thus ramping the output voltage. when the output voltage reaches the nominal value and v fb gets an input voltage of more than 300mv, the monostable is forced ? on ? from comp1 through gate u1, until the feedback voltage falls below 300mv. the above action continues to maintain regulation. eor, end of regulation detector the eor circuit is a retriggerable 120s monostable, which is re-triggered by every down regulating action of comparator comp1. as long as regulation takes place, output eor is ? high ? (high impedance, 100k to v cc ). short dips of the output voltage of less than 120s are ignored. if the output voltage falls below the nominal value for more than 120s, output eor goes ? low ? . the reason for this to happen is usually a slowly progressing drop of input voltage from the discharging battery. therefore the output voltage will also start to drop slowly. with the eor detector, batteries can be used to the ultimate end of discharge, with enough time left for a safe shutdown. block diagrams zxsc410 zxsc420 semiconductors issue 2 - may 2003 4 + _ + _ r2 r3 r1 stdn vcc drive sense gnd v fb shutdown bandgap reference bias generator comp 1 comp 2 u1 dynamic drive monostable 2s fig. 1 zxsc410 fig. 1 zxsc420
applications information switching transistor selection the choice of switching transistor has a major impact on the converter efficiency. for optimum performance, a bipolar transistor with low v ce(sat) and high gain is required. the v ceo of the switching transistor is also an important parameter as this sees the full output voltage when the transistor is switched off. zetex supersot ? transistors are an ideal choice for this application. schottky diode selection as with the switching transistor, the schottky rectifier diode has a major impact on the converter efficiency. a schottky diode with a low forward voltage and fast recovery time should be used for this application. the diode should be selected so that the maximum forward current rating is greater or equal to the maximum peak current in the inductor, and the maximum reverse voltage is greater or equal to the output voltage. the zetex zhcs series meet these needs. combination devices to minimise the external component count zetex recommends the zx3cdbs1m832 combination of npn transistor and schottky diode in a 3mm x 2mm mlp package. this device is recommended for use in space critical applications. the ic is also capable of driving mosfets. zetex recommends the zxmns3bm832 combination of low threshold voltage n-channel mosfet and schottky diode in a 3mm x 2mm mlp package. this device is recommended for use in space critical applications. inductor selection the inductor value must be chosen to satisfy performance, cost and size requirements of the overall solution. inductor selection has a significant impact on the converter performance. for applications where efficiency is critical, an inductor with a series resistance of 500m or less should be used. a list of recommended inductors is listed in the table below: peak current definition in general, the i pk value must be chosen to ensure that the switching transistor, q1, is in full saturation with maximum output power conditions, assuming worse-case input voltage and transistor gain under all operating temperature extremes. once i pk is decided the value of r sense can be determined by: r sense v sense i pk = zxsc410 zxsc420 semiconductors issue 2 - may 2003 5 pin no. name description 1v cc supply voltage, 1.8v to 8v. 2 gnd ground 3 stdn/eor shutdown zxsc410 / end of regulation zxsc420 4 sense inductor current sense input. internal threshold voltage set to 28mv. connect external sense resistor. 5v fb reference voltage. internal threshold set to 300mv. connect external resistor network to set output voltage. 6 drive drive output for external switching transistor. connect to base or gate of external switching transistor. part no. manufacture l i pk (a) r dc ( ) cmd4d11-100mc sumida 10h 0.5 0.457 cmd4d11-220mc sumida 22h 0.4 0.676 lpo2506ob-103 coilcraft 10h 1.0 0.24 st2006103 standex electronics inc 10h 0.6 0.1 pin descriptions
sense resistor a low value sense resistor is required to set the peak current. power in this resistor is negligible due to the low sense voltage threshold, v sense . below is a table of recommended sense resistors: output power calculation by making the above assumptions for inductance and peak current the output power can be determined by: p out = i av x v in x = (watts) where i i 2 x (t t (t t av pk on dis on off = + + ) ) and t ixl v on pk in = and t ixl v-v dis pk out in = and t off ? 1.7s (internally set by zxsc410) and = efficiency i.e. 100% = 1 operating frequency can be derived by: f 1 tt on off = + output capacitors output capacitors are a critical choice in the overall performance of the solution. they are required to filter the output and supply load transient currents. there are three parameters which are paramount in the selection of the output capacitors, capacitance, i ripple and esr. the capacitance value is selected to meet the load transient requirements. the capacitors i ripple rating must meet or exceed the current ripple of the solution. the esr of the output capacitor can also affect loop stability and transient performance. the capacitors selected for the solutions, and indicated in the reference designs, are optimised to provide the best overall performance. input capacitors the input capacitor is chosen for its voltage and rms current rating. the use of low esr electrolitic or tantalum capacitors is recommended. capacitor values for optimum performance are suggested in the reference design section also note that the esr of the input capcitor is effectively in series with the input and hence contributes to efficiency losses in the order of i rms 2 . esr. zxsc410 zxsc420 semiconductors issue 2 - may 2003 6 manufacture series r dc ( ) range size tolerance url cyntec rl1220 0.022 - 10 0805 5% http://www.cyntec.com irc lr1206 0.010 - 1.0 1206 5% http://www.ictt.com
output voltage adjustment the zxsc410/420 are adjustable output converters allowing the end user the maximum flexibilty. for adjustable operation a potential divider network is connected as follows: the output voltage is determined by the equation: vv1 ra rb out fb =+ ? ? ? ? ? ? where v fb =300mv the resistor values, ra and rb, should be maximised to improve efficiency and decrease battery drain. optimisation can be achieved by providing a minimum current of i fb(max) =200na to the v fb pin. output is adjustable from v fb to the (br)vceo of the switching transistor, q1. note: for the reference designs, ra is assigned the label r2 and rb the label r3. layout issues layout is critical for the circuit to function in the most efficient manner in terms of electrical efficiency, thermal considerations and noise. for ? step-up converters ? there are four main current loops, the input loop, power-switch loop, rectifier loop and output loop. the supply charging the input capacitor forms the input loop. the power-switch loop is defined when q1 is ? on ? , current flows from the input through the inductor, q1, r sense and to ground. when q1 is ? off ? , the energy stored in the inductor is transferred to the output capacitor and load via d1, forming the rectifier loop. the output loop is formed by the output capacitor supplying the load when q1 is switched back off. to optimise for best performance each of these loops kept separate from each other and interconnected with short, thick traces thus minimising parasitic inductance, capacitance and resistance. also the r sense resistor should be connected, with minimum trace length, between emitter lead of q1 and ground, again minimising stray parasitics. zxsc410 zxsc420 semiconductors issue 2 - may 2003 7 r b v fb gnd v out r a stdn gnd v cc drive sense v fb eor gnd v cc drive sense v fb zxsc410 sot23-6 zxsc420 sot23-6 connection diagrams
zxsc410 zxsc420 semiconductors issue 2 - may 2003 8 ref value part number manufacture comments u1 zxsc410e6 zetex dc-dc converter ic u2 zx3cdbs1m832 zetex low sat npn + 1a schottky l1 22h cmd4d11-220 sumida 1mm height profile r1 100m ? lr1206 / rl1220 irc / cyntec 1206 / 0805 size r2 16k ? generic generic 0603 size r3 1k ? generic generic 0603 size c1 22f/6v3 grm series murata 1206 size c2 22f/6v3 grm series murata 1206 size c3 1nf generic generic 0603 size reference designs zxsc410 dc-dc controller v in =2.5v to 4.2v v out =5v; i load =100ma bill of materials
zxsc410 zxsc420 semiconductors issue 2 - may 2003 9 v=1v/div; t=10s/div switching waveform v=50mv/div; t=10s/div output ripple performance graphs
zxsc410 zxsc420 semiconductors issue 2 - may 2003 10 a vdd =9v/180ma v on =18v/10ma v off =9v/10ma a vdd =9v/180ma v on =27v/10ma v off =9v/10ma zxsc410 as triple output tft bias zxsc410 as triple output tft bias
zxsc410 zxsc420 semiconductors issue 2 - may 2003 11 sequencing a vdd and v on by adding the circuit below to the lcd bias output (v on )of the converter a 10ms delay can be achieved between a vdd power up and v on power up. the circuit operates by a delay in turning the pmos transistor on, which transfers to a 10ms delay between input and output of the circuit. the delay is set by the rc time constant of r1 and c1. the diode, d1, discharges the gate of the pmos when the main system supply is turned off, guaranteeing a delay every turn on cycle.
zxsc410 zxsc420 semiconductors 12 issue 2 - may 2003 europe zetex plc fields new road chadderton oldham, ol9 8np united kingdom telephone (44) 161 622 4444 fax: (44) 161 622 4446 hq@zetex.com zetex gmbh streitfeldstra ? e19 d-81673 m nchen germany telefon: (49) 89 45 49 49 0 fax: (49) 89 45 49 49 49 europe.sales@zetex.com americas zetex inc 700 veterans memorial hwy hauppauge, ny 11788 usa telephone: (1) 631 360 2222 fax: (1) 631 360 8222 usa.sales@zetex.com asia pacific zetex (asia) ltd 3701-04 metroplaza tower 1 hing fong road kwai fong hong kong telephone: (852) 26100 611 fax: (852) 24250 494 asia.sales@zetex.com these offices are supported by agents and distributors in major countries world-wide. this publication is issued to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. the company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. for the latest product information, log on to www.zetex.com ? zetex plc 2003 dim millimetres inches dim millimetres inches min max min max min max min max a 0.90 1.45 0.35 0.057 e 2.60 3.00 0.102 0.118 a1 0.00 0.15 0 0.006 e1 1.50 1.75 0.059 0.069 a2 0.90 1.30 0.035 0.051 l 0.10 0.60 0.004 0.002 b 0.35 0.50 0.014 0.019 e 0.95 ref 0.037 ref c 0.09 0.20 0.0035 0.008 e1 1.90 ref 0.074 ref d 2.80 3.00 0.110 0.118 l 0 10 0 10 package dimensions controlling dimensions in millimetres approx conversions inches. a1 2 l datum a a c e aa2 e1 d b e e1 package outline pad layout details

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