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1/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. large current external fet contro ller type switching regulators single/dual-output high-frequency step-down switching regulator(controller type) bd9845fv overview bd9845fv is an ic containing a circuit of switching regulator controller by pulse width modulation system. this circuit can be used for step-down dc/dc converter operation. in addition, the package is designed compact, and is optimum for compact power supply for many kinds of equipment. feature 1) high voltage resistance input (vcc=35v) 2) fet driver circuit is contained (step-down circuit 1 output). 3) error amplifier reference voltage (1.0v ? 1%) and reg output circuit (2.5v) are contained. 4) overcurrent detection circuit is contained. 5) soft start and pause period can be adjusted. 6) three modes of standby, master, and slave can be switched. (iccs = 0 ua typ in standby mode.) 7) on/off control is enabled independently for each channel. (dt terminal) application lcd, pdp, pc, av, printer, dvd, projector tv, fax, copy machine, measuring instrument, etc. absolute maximum rating item symbol rating unit supply voltage vcc 36 v permissible loss pd 500 1 mw out terminal voltage resistance out vcc-7v to vcc v c5v terminal voltage resistance c5v vcc-7v to vcc v operation temperature range topr -40 to +85 c storage temperature range tstg -55 to +150 c joint temperature tjmax 150 c *1 when glass epoxy board 70.0 mm ? 70.0 mm ? 1.6 mm is installed onboard. r educed by 4.0 mw/c above ta=25 ? c. operating condition (ta=25 ?c) item symbol range unit supply voltage vcc 3.6 to 35 v output terminal voltage out c5v ? vcc v timing capacity cct 47 to 3000 pf oscillation frequency fosc 100 to 1500 khz stb input voltage vstb 0 to vcc v sel input voltage vseltb 0 to vcc v no.11028edt08
bd9845fv technical note 2/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. electric characteristics (ta=25 ? c, vcc=6v unless otherwise specified) item symbol standard value unit condition min. typ. max. [vref output unit] output voltage v ref 2.450 2.500 2.550 v i o =0.1 ma input stability line reg. 1 10 mv vcc=3.6 v 35 v load stability load reg. 2 10 mv i o =0.1 ma 2 ma current capacity i omax 2 13 ma v ref =(typ.) 0.95 [triangular wave oscillator] oscillation frequency f osc 95 106 117 khz c cp =1800 pf frequency fluctuation f dv 0 1 % vcc=3.6 v 35 v [soft start unit] ss source current i ssso 1.4 2 2.6 a ss=0.5 v ss sink current i sssi 5 12 ma ss=0.5 v [pause period adjusting circuit] dt input bias current i dt 0.1 1 a dt=1.75 v dt sink current i dtsi 1 3.3 ma dt=1.75 v, (ocp+)-(ocp-)=0.5 v [low input malfunction preventing circuit] threshold voltage v uth 3.0 3.2 3.4 v vcc start detection hysteresis v uhys 0.15 0.25 v [error amplifier] non-inverting input reference voltage v inv 0.99 1 1.01 v inv=fb reference voltage supply fluctuation dvinv 1 6 mv vcc=3.6 v 35 v inv input bias current i ib 0 1 a inv=1 v open gain av 65 85 db max output voltage v fbh 2.30 vref v min output voltage v fbl 0.6 1.3 v output sink current i fbsi 0.5 1.5 ma fb=1.25 v, inv=1.5 v output source current i fbso 50 105 a fb=1.25 v, inv=0.5 v [pwm comparator] input threshold vo ltage(fosc=100khz) vt 0 1.4 1.5 1.6 v on duty 0% vt 100 1.9 2 2.1 v on duty 100% [output unit] output on resistance h r onh 4.0 10 ? r onh =(v cc -out)/ iout, iout=0.1 a output on resistance l r onl 3.3 10 ? r onl =(out-c5 v)/ iout, iout=0.1 a c5v clamp voltage v clmp 4.5 5 5.5 v v clmp = v cc -c5v , v cc 7 v [overcurrent protection circuit] overcurrent detection threshold voltage v ocpth 0.04 0.05 0.06 v voltage between(ocp+) and (ocp-) ocp-input bias current i ocp - 0.1 10 a ocp+= v cc, ocp-= v cc -0.5 v overcurrent detection delay time tdocpth 200 400 ns ocp-= v cc v cc -0.2 v overcurrent detection minimum retention time tdocpre 0.8 1.6 ms ocp-= v cc -0.2 v v cc [standby changeover unit] stb flow-in current i stb - 55 100 a stb=6v standby mode setting range v stbl 0 - 0.5 v active (master) mode setting range v stbh 3.0 - v cc v sel flow-in current i sel - 15 30 a sel=2.5v master mode setting range v sell 0 - 0.5 v slave mode setting range v selh 2.0 - v cc v [device overall] standby current i ccs 0 1 a stb=0 v average power consumption i cca 1 2.4 4 ma inv=0 v, fb=h, dt=1.75 v * radiation resistance de sign is not applied.
bd9845fv technical note 3/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. 2.480 2.485 2.490 2.495 2.500 2.505 2.510 2.515 2.520 0 5 10 15 20 25 30 35 40 supply voltage: vcc(v) reference voltage: vref(v) ta=25c 0 1 2 3 4 5 6 7 8 9 10 -50 -25 0 25 50 75 100 125 ambient temperature: ta(c) standby current: iccs(ua) vcc=6v 0 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 35 40 supply voltage: vcc(v) circuit current: icca(ma) ta=25c 0 1 2 3 4 5 6 7 8 -50 -25 0 25 50 75 100 125 ambient temperature: ta(c) circuit current: icca(ma) vcc=6v 2.480 2.485 2.490 2.495 2.500 2.505 2.510 2.515 2.520 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 reference output current: iref(ma) reference voltage: vref(v) ta=25c vcc=6v 2.480 2.485 2.490 2.495 2.500 2.505 2.510 2.515 2.520 -50 -25 0 25 50 75 100 125 ambient temperature: ta(c) reference output voltage: vref (v) vcc=6v 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 -50 -25 0 25 50 75 100 125 ambient temperature: ta(c) uvlo threshold: vuth(v) 0.99 0.992 0.994 0.996 0.998 1 1.002 1.004 1.006 1.008 1.01 -50 -25 0 25 50 75 100 125 ambient temperature: ta(c) erramp reference voltage: vinv(v) vcc=6v 0 20 40 60 80 100 120 140 0 1 2 3 4 erramp output voltage: vfb(v) fb source current: ifbso(a) ta=85c ta=25c ta=-40c vcc=6.0v -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 0.5 1 1.5 2 erramp output voltage: vfb(v) fb sinkt current: ifbsi(ma) vcc=6.0v ta=85c ta=25c ta=-40c reference data 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 erramp input voltage: vinv(v) erramp input current: iib(a) fig.1 standby current temperature characteristics fig.2 circuit current in operation fig.3 circuit current temperature characteristics in operation fig.4 vref supply voltage characteristics fig.5 vref current capability fig.6 vref temperature characteristics fig.7 uvlo threshold temperature characteristics fig.8 error amplifier i/o characteristics fig.11 fb output source current fig.12 fb output sink current fig.10 error amplifier reference voltage temperature characteristics fig.9 error amplifier input current ta=25 phase gain -20 0 20 40 60 80 100 frequency [hz] loop gain :closed [ db ] -270 -225 -180 -135 -90 -45 0 phase shift [ deg ] 100 1k 10k 100k 1m 10m vcc=6v phase gain
bd9845fv technical note 4/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 ss voltage: vss(v) ss source current: issso(a) vcc=6.0v 0 5 10 15 20 25 30 35 0 0.5 1 1.5 2 ss voltage: vss(v) ss sink current: isssi(ma) vcc=6.0v ta=85c ta=25c ta=-40c 80 90 100 110 120 -50 -25 0 25 50 75 100 125 ambient temperature: ta(c) frequency: fosc(khz) vcc=6v ccp=1800pf 0 1 2 3 4 5 6 7 0 0.5 1 1.5 2 2.5 dt input voltage: vdt(v) dt input current: idt(a) vcc=6.0v ta=25c 0 1 2 3 4 5 6 7 0 0.5 1 1.5 2 2.5 dt input voltage: vdt(v) dt sink current: idt(ma) ta=85c ta=25c ta=-40c vcc=6.0v 0 10 20 30 40 50 60 70 80 90 100 1.4 1.6 1.8 2 2.2 dt input voltage: vdt(v) output duty cycle: duty(%) vcc=6.0v ta=25c 0 10 20 30 40 50 60 70 80 90 100 1.4 1.6 1.8 2 2.2 dt input voltage: vdt(v) output duty cycle:duty(%) vcc=6.0v ta=25c 0 5 10 15 20 25 30 35 40 vcc -0.05 -0.10 -0.15 -0.20 vout(v) ids(ma) ta=85c ta=25c ta=-40c vcc=6.0v vcc vcc vcc vcc ta=25c 0 5 10 15 20 25 30 35 40 c5v -0.05 -0.10 -0.15 -0.20 vout(v) ids(ma) ta=85c ta=25c ta=-40c vcc=6.0v c5v c5v c5v c5v 30 35 40 45 50 55 60 65 70 -50 -25 0 25 50 75 100 125 ambient temperature: ta(c) ocp threshold: vocpth(mv) vcc=6v reference data fig.14 ss sink current fig.13 ss source current fig.16 oscillation frequency temperature characteristics fig.17 dt bias current fig.18 dt sink current fig.19 output duty-vdt characteristics (100khz) fig.23 stb flow-in current fig.24 overcurrent detection voltage temperature characteristics fig.21 output on resistance h (ronh) fig.22 output on resistance l (ronh) fig.20 output duty-vdt characteristics (1.5mhz) 0 1 2 3 4 5 -50-25 0 25 50 75100125 ambient temperature: ta(c) ss source current: issso(ua) vcc=6.0v fig.15 ss source current temperature characteristics 0 50 100 150 200 250 300 350 400 450 500 0 5 10 15 20 25 30 35 40 vstb(v) istb(ua) ta=85 ta=25 ta=-40 vcc=35 v
bd9845fv technical note 5/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 50 100 150 200 250 ic5v(ma) vc5v(v) vcc=5.0v ta=25c 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 0 5 10 15 20 25 30 35 40 ic5v(ma) vcc-vc5v(v) vcc=6.0v ta = 2 5 c reference data fig.26 c5v load regulation fig.27 c5v line regulation fig.25 c5v saturation voltage 0 1 2 3 4 5 6 7 8 9 10 0 5 10 15 20 25 30 35 40 supply voltage: vcc(v) vcc-vc5v(v) ta=25c
bd9845fv technical note 6/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. block diagram/pin layout terminal number terminal name function 1 vref reference voltage (2.5v) output terminal 2 ct timing capacity external terminal 3 gnd ground 4 stb standby mode setting terminal 5 c5v output l side voltage (vcc-5v) 6 out output 7 vcc power terminal 8 ocp output overcurrent detector + input terminal 9 ocp output overcurrent detector - input terminal 10 sel master/slave mode setting terminal 11 fb output error amplifier output terminal 12 inv output error amplifier - input terminal 13 ss output soft start time setting terminal 14 dt output dead time setting terminal fig.28 block diagram fig.29 pin layout + + - err + + - pwm ls drv vref 2a vcc c5v ocp c5v vcc ocp + - vref vcc c5v reg (2.5v) vref dt fb ss inv ct vcc vcc ocp+ ocp- gnd out c5v 1v10mv 50mv10mv reg (vcc-5v) dtoff ssoff tsd tsd 2v 1.5v + - master /slave + - - 200a 200a 1.5v 2.0v master /slave osc hold time (1.6msec) ocp dtlow ssoff dtoff uvlo tsd hold time (0.2msec) protection logic uvlo uvlo vcc vref c5v 3.2v 2.2v 3v + - dtlow 1.25v dt stb stb sel dt ss inv fb sel ocp- vref ct gnd stb c5v out ocp+ vcc ssop-b14
bd9845fv technical note 7/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. 10 100 1000 10000 10 100 1000 10000 ct timing capacity (pf) oscillation frequency (khz) ta=25 vo r 1 r 2 12 11 inv fb erramp rf cf 1v operation description of each block and function 1) reg (reference voltage unit) as for reg (2.5v), reference voltage (2.5v) stabilized better t han supply voltage input to vcc terminal is supplied as an operation voltage of ic internal circuit, as well as output outside through vref terminal. insert a capacitor of 1uf to vref terminal. as for reg (vcc-5v), voltage of vcc-5v is supplied as powe r supply (ldo) of driver circuit (drv) of out terminal, as well as output outside through c5v te rminal. insert a capacitor of 1uf to vcc terminal of c5v terminal. 2) err amp (error amplifier) in step-down application, inverting input inv of error amplifier detects output voltage by sending back feedback current from final output stage (on load side) of switching regulator. r1 and r2 connected to this input terminal are resistor for setting output voltage. non-inverting input of amplifier is a reference input of error amplifier itself by adding reference voltage (1.0v) inside ic. rf and cf connected betw een fb, which is output from error amplifier, and inv are for feedback of error amplifier, and allows setting of loop gain. fb is connected to pwm comp and supplied as non-inverting input. setting of output voltage (vo) is as follows: vo = ? 1.0v 3) osc (triangular wave oscillating unit) generates triangular wave for inputting to pwm comp. first, timing capacitor c ct connected between ct terminal and gnd is ch arged by constant current (200 ua) generated inside ic. when ct voltage reaches 2.0 v ty p, the comparator is switched, and then c ct is discharged by constant current (200 a). then, when ct voltage reaches 1.5v, the comparator is switched again, and c ct is charged again. this repetition generates triangular wave. oscillation frequency is determined by externally mounted c ct through theoretical formula below: fosc P ict/(2 ?c ct ? vosc) ict : ct sink/source current 200 ua typ vosc : triangular wave amplifying voltage (vt0-vt100) 0.50 v typ. here, error from theoretical formula is caused by delay of internal circuit at a high frequency. see the graph in fig 31 for setting. this triangular wave can be taken out through ct terminal. it is also possible to input the oscillator externally by switching to slave mode described later. waveform input here in principle must be triangular wave of vpeak = (1.5v ? 2.0v) equivalent to internal oscillation circuit. external input voltage range v ct : 1.4 v < v ct < 2.3 v standard external c ct range c ct : min.47 pf ? max.3000 pf r2 r1 + r2 fig.30 fig.31
bd9845fv technical note 8/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. 4) soft start (soft start function) it is possible to provide ss terminal (13pin) with soft start function by connecting c ss as shown on the right. soft start time tss is shown by the formula below: tss = css ? (ex) when css = 0.01 uf tss = = 5 [msec] in order to function soft start, time must be set longer enough than start time of power supply and stb. it is also possible to provide function of soft start by connecting the resistor (r1/r2) and capacitor (c dt ) to dt terminal (14pin) as shown on the right. 5) pwm comp - dead time (pause period adjusting circuit - dead time) dead time can be set by applying voltage dividing resistance between vref and gnd to dt terminal. pwm comp compares the input dead time voltage (dt terminal voltage) and error voltage from err amp (fb terminal voltage) with triangular wave, and turns off and on the output. when dead time voltage < error voltage, duty of output is determined by dead time voltage. (when dead time setting is not used, pull up dt terminal to vref terminal with resistor approx 10 k ohms.) dead time voltage vdt in fig 32 is shown by the formula below: vdt vref ? relation between vdt and duty [see the graph on the right.] duty 100% duty 0% min typ max min typ max when f = 100khz 1.9 2. 0 2.1 1.4 1.5 1.6 when f = 1.5mhz 1.95 2. 1 2.25 1.35 1.5 1.65 be careful when oscillation frequency is high, upper/lower limit of triangular wave (vt100/vt0) is shifted by delay time of comparator to directions expanding amplitude. 6) ocp comp (overcurre nt detection circuit) this function provides protection by forcibly turning off the output when abnormal overcurrent flows due to shorting of output, etc. when voltage between terminal ocp+(8pin)/ocp-(9pin) monitoring the current with sense resistor exceeds overcurrent de tection voltage (50 mv typ), it is determined as overcurrent condition, and switching operation is stopped immediately by setting out to "h" and dt,ss (and fb) to "l". it is automatically recovered when voltage between terminal ocp+/ocp- is below overcurrent detection voltage. in addition, although hysteresis, etc. are not set here, minimum detection retention time (1.6ms typ) is set fo r suppressing the heatin g of fet, etc. (see the timing chart.) when the overcurrent detection circui t is not used, short-circuit both terminal ocp+/ocp- to vcc pin. r1 r2 r2 issso vinv css : ss terminal connection capacity vinv : error amplifier reference voltage (1v typ) issso : ss source current (2ua typ) 2 10 -6 0.0110 -6 1 fig.32 fig.33 [unit : v] 1 1.2 1.4 1.6 1.8 2 2.2 2.4 100 1000 10000 fosc[khz] vdt[v] vt100 vt0 fig.34 fig.35 direction of current sense resisto r vref dt r 1 r 2 c dt 1 14 vref inv ss erramp 2ua css 1vtyp. 13 12 vin ocp+ ocp- ocp comp 50mvtyp. 8 9
bd9845fv technical note 9/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. 7) stb /sel(standby/master/slave function) standby mode and normal mode can be switched by stb terminal (4pin). 1. when stb<0.5v, standby mode is set. out put stop (out=h) and reg also stops. cir cuit current is also isc = 0 ua here. 2. when stb>3.0v, normal operation mode is set. all circuits operate. use the cont roller normally in this range. master mode and slave mode can be switched by sel terminal (10pin). 1. when sel<0.5v, master mode is set. all circuits operate. 2. when sel>0.5v, slave mode is set. operation status is set , but osc block alone is stopped, ct terminal is high-z here, and triangular wave is not output.(pwm circuit and protection circuit perform the same oper ation as usual.) therefore, if the controller is used in this more without using master ic, triangular wave is no t emitted, operation is unstabl e, and normal output cannot be obtained. be careful. 8) out (output: external fet gate drive) out terminal (6pin) is capable of directly driving the gate of external (pchmos) fet. amplit ude of output is restricted between vcc and c5v (vcc-5v), and is not restricted by voltage resistance of gate by input voltage, which allows broad selection of fet. however, for precaution when selecting fet, there is a restriction that input capacity of gate is determined by current capability of c5v and permissible loss of ic, therefore refer to the permissi ble range in the graph on the right when determining fet. 9) protection (other protection functions) this ic is equipped with low input malfunction prevention circuit (uvlo) and abnormal temperature protection circuit (tsd) in addition to overcurrent detection circuit (ocp). low input malfunction prevention circuit is for prev enting unstable output when input voltage is low. three positions of vcc (3.2v), vref(2.35v), and c5v(vcc-3v ) are monitored, and output is made only when all are canceled. (see the timing chart.) abnormal temperature protection circuit is for protecting ic chip from destruction for preventing runaway when abnormal heating is caused on ic exceeding rated tem perature. (it does not operate normally.) apply a design with full margin allowed for heating in consideration of permissible loss. fig.35 out ?S? 1.e-10 1.e-09 1.e-08 1.e-07 100 1000 10000 switching f requency [khz] out terminal permissible capacity [f] cout_max cout_max (vcc=10v) cout_max (vcc=20v) cout_max ( vcc=30v ) permissible range area below each line under each condition fig.36
bd9845fv technical note 10/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. timing chart item min typ max threshold voltage (vcc) 3.0 3.2 3.4 hysteresis - 0.15 0.25 threshold voltage (vref) 2.0 2.2 2.4 threshold voltage (c5v) - 3.0 3.4 overcurrent detection (when output is shorted: overcurrent detection and cancel ar e repeated at a specified time interval.) starting characteristics (uvlo cancel) and standby operation stb vref 1v ss dt fb ct vcc vcc-5v out c5v c5v dtuvlog?? fbuvlog?? :uvlogvref???? out vref2.2vuvlo(vref) uvlo(tsd)?rg(0.2msec) uvlo(vcc,vref)??? (vcc-5v)reg c5vvcc-3vuvlo(c5v) 1.8vtyp. 0.9vtyp. ct uvloo?B vcc vcc3.2vuvlo(vcc) vref?R vref???R uvlo? vccvrefc5v????B?????rg? vccvrefc5v?uvlo??????? ss???O? ??`???rgS???? gH??????LrgO? uvlo voltage [unit: v] (1) uvlo (vcc) is canceled when vcc>3.2v. (2) uvlo (vref) is canceled when vref>2.2v. ? uvlo (tsd) minimum retention time (0.2 ms) set ss by external capacity. a lthough ss is notated by the same time axis in the figure for showing the image, actually set sufficiently longer time in comparison with the cycle of triangular wave. ? uvlo uvlo ct: pull-up to vref during uvlo period dt: pull-down during uvlo fb: pull-down during uvlo when uvlo (vcc , and vref) is canceled, (vcc - 5v) reg is started. (3) uvlo (c5v) is canceled when c5v bd9845fv technical note 11/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. example of application circuit fig.37 1) setting of output unit coil (l) and capacitor (co) set the coil and capacitor as follows in step-down application: when load current gets heavy, the current flowing through the co il gets continuous, and the relation below is established: l = ? normally set delta il below 30% of the maximum output current (iomax). when l-value is made greater, ripple current (delta il) becomes smaller. in general, the greater the l-value is, the smaller the permissible current of coil gets, and when the current exceeds permissible current, the coil is saturated and l-value changes. contact the coil manufacturer and check permissible current. select an output capacitor co by esr (equivalent serial resistance) property of capacitor. output ripple voltage (delta vo) is almo st esr of output capacitor, therefore, ? vo P ? il esr esr: equivalent serial resi stance of output capacitor co the relation above is established. ripple component by output capacitor is small enough to be neglected in comparison with ripple component by esr in many cases. as for co value, it is re commended to use a sufficiently large capaci tor with a capacity that satisfies esr condition. determine a switching element by peak current. peak current isw flowing through the switching element is equal to peak current flowing through the coil, t herefore the equation below is established. isw (peak) = io + ? il/2 select a switching element of permissible current having a suffic ient margin over peak current calculated by the equation. osc + - + pwm drv vcc vcc-5v + - + err vref uvlo tsd ocp2 vcc-5v vcc ocp - + vref vcc vcc-5v vref vref ct inv ss fb dt vcc vcc stb ocp+ ocp- gnd out c5v vin vo (step-down) 5vreg ? il ts w vin (vin-vo)vo vin: input voltage tsw: 1/(switching frequency) delta il: ripple current of coil
bd9845fv technical note 12/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. d t ss dtcomp to out for each ch each ch control signal digital transistor, etc. 14 13 1.25vtyp. vref fig 41. example of master/slave 2) example of overcurrent protection circuit insert a sense resistor between the source and vin of output pch-fet for detecting overcurrent as shown in the figure. refer to the formula below for determining a sense resistor and select permissible loss ensuring a margin. rsense iocp is a peak current isw (peak) here, and the amperage for output load is an overcurrent setting amperage minus ripple current component (delta i l /2), etc. (see the formula on p10.) there is a time delay approx 200ns from detection until stop of output is made (pulse of approx 100 ns causes delay time but detection is made), and an error may be caused from the value above. in addition, input to overcurrent detection unit is such a sensitive circuit, and wrong detection by noise may be possible. when wrong detection occurs, try to eliminate noise by the resistor r1 and r2 or capacitance c1, c2, c3, and c4 shown above. 3) example of output on/off control circuit when stopping the whole circuit, set stb terminal to "low (stb<0.5v) to stop switching and reduce power consumption of ic to 0 microa (typ). also when switching on and off for each channel, control is fixed to off by setting dt terminal of desired channel to "low (dt<1.25v)". this control is independent for each channel, and when dt="l", ss terminal and fb terminal are also discharged, and soft start is enabled in restarting. 4) example of master/slave (syn c multi-ch output) operation circuit this ic is set to slave mode by setti ng the input of stb terminal at 2.5v ? 0.1v, and multi-channel output is enabled with frequency synchronized. (fig.40) however, ct terminal has high impedance in slave mode status, and triangular wave is generated by ct waveform of master mode ic. therefore t he example of master slave circuit below is recommended when starting and stopping in order to avoid malfunction by star t/stop timing of master ic and slave ic. as for output, it is recommended to control on/off reliably with dt terminal. also, oscillation frequency is determined by capacitor (c ct ) connected to ct. when the slave ic is large in number as well as oscillation frequency is high, parasitic capacity by board wiring in contact with ct cannot be ignored, and preset frequency may be drifted. be careful. example of master/slave circuit configuration is shown below. if any other configuration is to be applied, inform our personnel in charge. vin r1 ocp+ ocp- out c1 r2 c2 c3 ??? ocp comp vocpth=50mv 8 9 6 c4 iocp vocpth vocpth : overcurrent detection voltage (50 mv typ) iocp : overcurrent detection setting current fig.38 sense resisto r fig.39 fig.40 ??? high?R2.5v?? stb ?ic ic n ct ct ? stb ? stb? master stb master ic common slave ic input a signal of high voltage 2.5v synchronized with master. sel stb ct vref dt master ic sel stb ct vref dt slave ic ch on/off control dtc114y c ct 0.1uf 10k 0.1uf 10k ch on/off control dtc114y stand-by on/off
bd9845fv technical note 13/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. 5) about board layout in order to make full use of ic performance, fully invest igate the items below in addition to general precautions. ? each output of ocp+/ocp- is such a sensitive circuit. when wiring is routed around, it is easily subjected to noise. try to make the wiring as short as possible. ? switching of large current is likely to generate noise. try to make the large current route (vin, rsense, fet, l, di, and cout) as thick and short as possible, and try to a pply one-point grounding for gnd. out terminal is also a switching line, and it must be wired along a distance as short as possible. (when multi-layer board is used, shielding by intermediate layer also seems to be effective.) ? c ct and c vref are reference of all, and must be wired along the shortest distance to gnd of ic stabilized to be protected against external influence. ? also be careful not to allow common impedance to sense family gnd. 6) pin processing of channel unused when only one channel is used, process unused channels as shown above. i/o equivalent circuit diagram 2pin(ct) 14pin (dt) 13pin (ss) 12pin (inv) 11pin (fb) 9pin (ocp-) 5pin (c5v) 6pin (out) 8pin (ocp+) 4pin (stb) 10pin (sel) 1pin (vref) 3pin (gnd) , 7pin (vcc) dt vref vref ss vref vref vref vcc ct vref vref vref vref vref inv vref vref fb vref vref ocp- vcc c5v c5v vcc ocp+ vcc c5v vcc c5v fig.43 vref vcc vcc vref vref dt ss inv fb ocp- ocp+ vcc out 1 14 13 12 11 9 8 7 6 c5v vcc vcc vcc vcc out vcc vcc c5v c5v vcc gnd vref vcc vcc sel vcc stb vcc
bd9845fv technical note 14/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. notes for use 1) about maximum absolute rating when the maximum absolute rating of application voltage or operation voltage range is exceeded, it may lead to deterioration or rupture. it is impossible to forecast rupt ure in short mode or open mode. when a special mode is expected exceeding the maximum absolute ra ting, try to take a physical safety measure such as a fuse. 2) gnd potential ensure that the potential of gnd terminal is the minimum in any operation conditi on. also ensure that no terminal except gnd terminal has a voltage below gnd volt age including actual transient phenomenon. 3) thermal design allow a sufficient margin in thermal design in consideration of permissible loss (pd) in actual use condition. 4) shorting between terminals and wrong attachment when attaching an ic to a set board, pay fu ll attention to the direction of ic and dislocation. wrong attachment may cause rupture of ic. in addition, when shorting is caused by foreign substance placed between outputs or between output and power supply-gnd, rupture is also possible. 5) operation in intense magnetic field use in intense magnetic field may re sult in malfunction. be careful. 6) inspection on set board in inspection on set board, when a capacitor is connected to a terminal with low impedance, stress may be applied to ic, therefore be sure to discharge electricity in each process. apply grounding to assembling process for a measure against static electricity, and take enough care in transport and stor age. when connecting a jig in inspection process, be sure to turn off power before detaching ic. 7) about ic terminal input this ic is a monolithic ic, and contains p + isolation and p board for separating elements between each element. this p-layer and n-layer of each element form p-n junction, and many kinds of parasitic elements are constituted. (see fig 43.) for example, when resistor and transistor are connected with a terminal as shown below. p-n junction operates as a parasitic diode when gnd>(terminal a) for resistor, and when gn d>(terminal b) for transistor (npn). in addition, when gnd>(terminal b) for transistor (npn), parasitic npn transistor is operated by n-layer of some other elements in the vicinity of parasitic diode mentioned above. parasitic element is inevitably generated by potential because of ic structure. operation of parasitic element causes interference with circuit operation, and may lead to malfunc tion, and also may cause rupture. therefore when applying a voltage lower than gnd (p board) to i/o terminal, pay full attent ion to usage so that parasi tic elements do not operate. fig.44 ??? npn) ?? ? b b a) ?? ? e c gnd gnd p p p gnd gnd gnd resistor (terminal a) (terminal b) (terminal b) (terminal a) p board p board parasitic element parasitic element parasitic element transistor (npn) parasitic element a nother element in the vicinity
bd9845fv technical note 15/15 www.rohm.com 2011.08 - rev.d ? 2011 rohm co., ltd. all rights reserved. ordering part number b d 9 8 4 5 f v - e 2 part no. part no. 9845 package fv : ssop-b14 packaging and forming specification e2: embossed tape and reel (ssop-b14) ? order quantity needs to be multiple of the minimum quantity. embossed carrier tape tape quantity direction of feed the direction is the 1pin of product is at the upper left when you hold reel on the left hand and you pull out the tape on the right hand 2500pcs e2 () direction of feed reel 1pin (unit : mm) ssop-b14 8 7 14 1 0.10 6.4 0.3 4.4 0.2 5.0 0.2 0.22 0.1 1.15 0.1 0.65 0.15 0.1 0.3min. 0.1
r1120 a www.rohm.com ? 2011 rohm co., ltd. all rights reserved. notice rohm customer support system http://www.rohm.com/contact/ thank you for your accessing to rohm product informations. more detail product informations and catalogs are available, please contact us. notes no copying or reproduction of this document, in part or in whole, is permitted without the consent of rohm co.,ltd. the content specied herein is subject to change for improvement without notice. the content specied herein is for the purpose of introducing rohm's products (hereinafter "products"). if you wish to use any such product, please be sure to refer to the specications, which can be obtained from rohm upon request. examples of application circuits, circuit constants and any other information contained herein illustrate the standard usage and operations of the products. the peripheral conditions must be taken into account when designing circuits for mass production. great care was taken in ensuring the accuracy of the information specied in this document. however, should you incur any damage arising from any inaccuracy or misprint of such information, rohm shall bear no responsibility for such damage. the technical information specied herein is intended only to show the typical functions of and examples of application circuits for the produc ts. rohm does not grant you, explicitly or implicitly, any license to use or exercise intellectual property or other rights held by rohm and other parties. rohm shall bear no responsibility whatsoever for any dispute arising from the use of such technical information. the products specied in this document are intended to be used with general-use electronic equipment or devices (such as audio visual equipment, ofce-automation equipment, commu- nication devices, electronic appliances and amusement devices). the products specied in this document are not designed to be radiation tolerant. while rohm always makes efforts to enhance the quality and reliability of its products, a product may fail or malfunction for a variety of reasons. please be sure to implement in your equipment using the products safety measures to guard against the possibility of physical injury, re or any other damage caused in the event of the failure of any product, such as derating, redundancy, re control and fail-safe designs. rohm shall bear no responsibility whatsoever for your use of any product outside of the prescribed scope or not in accordance with the instruction manual. the products are not designed or manufactured to be used with any equipment, device or system which requires an extremely high level of reliability the failure or malfunction of which may result in a direct threat to human life or create a risk of human injury (such as a medical instrument, transportation equipment, aerospace machinery, nuclear-reactor controller, fuel- controller or other safety device). rohm shall bear no responsibility in any way for use of any of the products for the above special purposes. if a product is intended to be used for any such special purpose, please contact a rohm sales representative before purchasing. if you intend to export or ship overseas any product or technology specied herein that may be controlled under the foreign exchange and the foreign trade law, you will be required to obtain a license or permit under the law.

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