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r1285l series 2ch dcdc for oled no.ea-209-090703 1 v 1.4 outline the r1285l 2ch dc/dc converter is designed for oled display power source. it contains a step up dc/dc converter and an inverting dc/dc converter to generat e two required voltages by oled display. step up dc/dc converter generates boosted output voltage to 4.6v ~ 5.0v. inverti ng dc/dc converter generates negative voltage ?2.0v ~ -6.0v independently. each of the r1285 series consists of an oscillator, a pwm control circuit, a voltage reference, error amplifiers, over curr ent protection circuits, shor t protection circuits, an under voltage lockout circuit (uvlo), a complete shutdown switch and an nch driver for boost operation, a pch driver for inverting, and so on. a high efficiency boost and invert ing dc/dc converter can be composed with external inductors, diodes, capacitors and resistor s. start up sequence is internally made. features operating voltage ? ? ? ? ? 2.3v ~ 4.8v step up dc/dc (ch1) internal pch mosfet for complete shutdown (ron=300m typ.) internal nch mosfet driver (ron=300m typ.) output voltage (v outp ) ? ? ? ? ? 4.6v ~ 5.0v (0.2vstep) auto discharge function for positive output internal soft start function (typ. 4.5ms) over current protection maximum duty cycle: 85%(typ.) inverting dc/dc (ch2) internal pch mosfet driver (ron=600m typ.) output voltage (v outn ) ? ? ? ? ? -2v ~ -6v (0.1vstep) [ r1285lxxxa ] adjustable vout up to -6v with external resistors [ r1285l00xb ] auto discharge function for negative output internal soft start function (typ. 4.5ms) over current protection maximum duty cycle: 90%(typ.) control short protection with timer latch function (typ. 50ms) short condition for either or both two outputs makes all output drivers off and latches. if the maximum duty cycle continues for a certain time , these output drivers will be turned off. this function prevents irregular curr ent from overheating the r1285 . ce with start up sequence function ( ch1 ch2 ) uvlo function. operating frequency ? ? ? ? ? 1400khz small package ? ? ? ? ? dfn12 ( 2.7mm x 3.0mm ) application fixed voltage power supply for portable equipment fixed voltage power supply for oled
r1285l 2 block diagram r1285lxxxa r1285l00xb pwm control time r maxdut y discharge control vref3 vref1 vref2 pwm control maxdut y current limit current limit osc sequence control soft start2 soft start1 enable control uvlo short protect pv cc l xn v outn ce l xp 1 l xp 2 pgnd v outp v cc gnd discharge control v fbn v ref pwm control time r maxdut y discharge control vref3 vref1 vref2 pwm control maxdut y current limit current limit osc sequence control soft start2 soft start1 enable control uvlo short protect pv cc l xn v outn ce l xp 1 l xp 2 pgnd v outp v cc gnd discharge control tst1 tst2
r1285l 3 selection guide the mask option for the ics can be selected at the user's request. the selection can be made with designating the part number as shown below. r1285l xx x x code contents a setting inverting output voltage (v outn ) stepwise setting with a step of 0.1v in the range of -2.0v to -6.0v is possible for fixed output version (r1285lxxxa) "00" is for output voltage adjustable version (r1285l00xb) b setting positive output voltage (v outp ) 1: 4.6v 2: 4.8v 3: 5.0v c designation of method of setting v outn a: fixed output version b: adjustable version pin configuration dfn -2730-12 b bottom view 1 2 3 4 5 6 7 8 9 10 11 12 part number a top view 1 2 3 4 5 6 7 8 9 10 11 12 c
r1285l 4 pin descriptions r1285lxxxa r1285l00xb pin no. name function 1 pgnd power gnd pin 2 v outp output voltage feedback pin for step up dc/dc 3 pv cc power input pin 4 v cc analog power source input pin 5 gnd analog gnd pin 6 ce chip enable pin 7 tst2 test pin 8 tst1 test pin 9 v outn output voltage feedback pin for inverting dc/dc 10 l xn switching pin for inverting dc/dc 11 l xp 1 shutdown switch output pin 12 l xp 2 switching pin for step up dc/dc pin no. name function 1 pgnd power gnd pin 2 v outp output voltage feedback pin for step up dc/dc 3 pv cc power input pin 4 v cc analog power source input pin 5 gnd analog gnd pin 6 ce chip enable pin 7 v ref reference voltage output pin for inverting dc/dc 8 v fbn feedback pin for inverting dc/dc 9 v outn output voltage feedback pin for inverting dc/dc 10 l xn switching pin for inverting dc/dc 11 l xp 1 shutdown switch output pin 12 l xp 2 switching pin for step up dc/dc
r1285l 5 absolute maximum ratings (gnd / pgnd=0v) item symbol rating unit v cc / pv cc pin voltage v cc 6.0 v v outp pin voltage v outp -0.3 ~ 6.0 v ce pin voltage v ce -0.3 ~ v cc +0.3 v l xp 1 pin voltage v lxp 1 -0.3 ~ v cc +0.3 v l xp 2 pin voltage v lxp 2 -0.3 ~ 6.0 v l xn pin voltage v lxn v cc -14 ~ v cc +0.3 v v outn pin voltage v outn v cc -14 ~ v cc +0.3 v tst1/tst2 pin voltage [r1285lxxxa] v tst -0.3 ~ v cc +0.3 v v fbn pin voltage [r1285l00xb] v fbn -0.7 *2 ~ v cc +0.3 v v ref pin voltage [r1285l00xb] v ref -0.7 *2 ~ v cc +0.3 v power dissipation *1 pd 1000 mw operating temperature range ta -40 ~ +85 oc storage temperature range tstg -55 ~ +125 oc ?1 ) for power dissipation, please refer to package information to be described. ?2 )in case the voltage range is from ?0.7v to ?0.3v, permissible current is 10ma or less. absolute maximum ratings absolute maximum ratings are threshold limit values that must not be exceeded ever for an instant under any conditions. moreover, such va lues for any two items must not be reached simultaneously. operation above these absolute maximum ratings may cause degradation or permanent damage to the device. these are stre ss ratings only and do not necessarily imply functional operation these limits.
r1285l 6 electrical characteristics (ta=25oc) symbol item conditions min. typ. max. unit. v cc operating input voltage 2.3 4.8 v i cc1 v cc consumption current ( switchin g) v cc =4.8v 4.0 ma i cc2 v cc consumption current ( at no switchin g) v cc =4.8v 350 ua i stb standby current v cc =4.8v 0.1 3 ua v uvlo 1 uvlo detect voltage falling 1.95 2.05 2.15 v v uvlo 2 uvlo released voltage rising v uvlo1 +0.10 2.28 v f osc oscillator frequency v cc =3.7v 1200 1400 1600 khz t dly delay time for protection v cc =3.7v 50 ms v cel ce ?l? input voltage v cc =2.3v 0.3 v v ceh ce ?h? input voltage v cc =4.8v 1.5 v r ce ce pin pulldown resistance v cc =3.7v 600 k boost dc/dc v outp v outp voltage tolerance v cc =3.7v x0.985 x1.015 v ? v outp / ? t v outp voltage temperature coefficient v cc =3.7v , -40oc < = < = 150 ppm / oc ? v outp / ? vcc v outp voltage line re g ulation 2.9v < = < = 4 mv ? v outp / ? i out v outp voltage load re g ulation v cc =3.7v , 10ma < = < = 10 mv ? v outp_tr v outp voltage line transient response v cc =2.9v ? 3.4v , t r =t f =50us 10 mv maxduty1 ch1 max. duty cycle v cc =3.7v 78 85 % t ss1 ch1 soft-start time v cc =3.7v 4.5 ms r lxp1 l xp 1 on resistance v cc =3.7v 300 m i off lxp1 l xp 1 leakage current v cc =4.8v , v lxp 1=0v 5 ua r lxp2 l xp 2 on resistance v cc =3.7v 300 m i off lxp2 l xp 2 leakage current v cc =4.8v , v lxp 2=5v 5 ua i limlxp2 l xp 2 current limit v cc =3.7v 0.7 1.0 a i voutp v outp discharge current v cc =3.7v , v outp =0.1v 10 ma
r1285l 7 inverting dc/dc [ r1285lxxxa] v outn v outn voltage tolerance v cc =3.7v x0.985 x1.015 ? v outn / ? t v outn voltage temperature coefficient v cc =3.7v , -40oc Q ta Q 85oc 150 ppm / oc ? v outn / ? vcc v outn voltage line re g ulation 2.9v Q v cc Q 3.4 6 mv ? v outn / ? i out v outn voltage load re g ulation v cc =3.7v , 10ma Q i out Q 100ma 15 mv ? v outn_tr v outn voltage line transient response v cc =2.9v ? 3.4v , t r =t f =50us 25 mv maxduty2 ch2 max. duty cycle v cc =3.7v 83 90 % t ss2 ch2 soft-start time v cc =3.7v 4.5 ms r lxn l xn on resistance v cc =3.7v 600 m i off lxn l xn leakage current v cc =4.8v , v lxn =-6v 5 ua i limlxn l xn current limit v cc =3.7v 1.0 1.5 a i voutn v outn discharge current v cc =3.7v , v outn =-0.3v 50 ma inverting dc/dc [ r1285l00xb] v fbn v fbn volta g e tolerance v cc =3.7v -25 0 25 mv i fbn v fbn in p ut current v cc =4.8v , v fbn =0v or 4.8v -0.1 0.1 a v ref v ref voltage tolerance v cc =3.7v 1.172 +v fbn 1.2 +v fbn 1.228 +v fbn v ? v ref / ? t v ref voltage tem p erature coefficient v cc =3.7v -40oc Q Q 150 ppm / oc ? v outn / ? v cc v outn voltage line regulation 2.9v Q v cc Q 3.4 6 mv ? v outn / ? i out v outn voltage load regulation v cc =3.7v , 10ma Q i out Q 100ma 15 mv ? v outn_tr v outn voltage line transient response v cc =2.9v ? 3.4v , t r =t f =50us 25 mv maxduty2 ch2 max. duty cycle v cc = 3.7v 83 90 % t ss2 ch2 soft-start time v cc = 3.7v 4.5 ms r lxn l xn on resistance v cc = 3.7v 600 m i off lxn l xn leakage current v cc =4.8v , v lxn =-6v 5 ua i limlxn l xn current limit v cc =3.7v 1.0 1.5 a i voutn v outn discharge current v cc =3.7v , v outn =-0.3v 50 ma * in terms of tst pin(tst1 , tst2), connect the gnd level or remain it open. recommended operating conditions (electrical characteristics) all of electronic equipment should be designed that the mount ed semiconductor devices operate within the recommended operating conditions. the semiconductor dev ices cannot operate norma lly over the recommended operating conditions, even if when they are used over such conditions by mom entary electronic noise or surge. and the semiconductor devices may receive serious damage when t hey continue to operate ov er the recommended operating conditions.
r1285l 8 pv cc l xn v outn ce l xp 1 l xp 2 pgnd v outp v cc gnd v outp v outn en control c1 4.7uf c2 10uf c3 10uf l1 l2 d1 d2 tst1 tst2 typical application and technical notes r1285lxxxa r1285l00xb set a ceramic 4.7 f or more capacitor between vcc and gnd as c1. set a ceramic10 f or more capacitor between v outp and gnd, and between v outn and gnd for each as c2 and c3. start up sequence when ce level turns from ?l? to ?h? level, the softstart of ch1 starts the operation. after detecting output voltage of ch1(v outp )as the nominal level, the soft st art of ch2 starts the operation. r1 r2 r3 c5 c4 pv cc l xn v outn ce l xp 1 l xp 2 pgnd v outp v cc gnd v outp v outn en control c1 4.7uf c2 10uf c3 10uf l1 l2 d1 d2 v fbn v ref ce 0v ch1 (v outp ) ch2 (v outn ) soft start ch1 soft start ch2
r1285l 9 auto discharge function when ce level turns from ?h? to ?l? level, the r 1285 goes into standby mode and sw itching of the outputs of l xp2 and l xn will stop. then dischage switsh between v outn and pv cc and switch between v outp and gnd turn on and discharge the negative output voltage and positive output voltage. when the negative output voltage is discharged to 0v, the switsh between v outn and pv cc turns off and the negative output will be hi-z. positive output voltage is discharged to 0v in standby mode. if vcc voltage became lower than uvlo detect voltage , discharge switches also turn on and discharge output voltage(v outn and v outp ) . in case of timer latch protecti on,discharge switches will keep off . short protection circuit timer in case that the voltage of v outp drops, the error amplifier of ch1 out puts "h". in case that the voltage of v outn rises, the error amplifier of ch2 outputs "l". the built-in short protection circuit makes the internal timer operate with detecting the output of the error amplifier of ch1 as "h", or the output of the error amplifier of ch2 as "l". after the se tting time will pass, the switching of l xp2 and l xn will stop and shutdown switch will turn off and both of discharge switches will keep off . to release the latch operation, make the vcc set equal or less than uvlo level and restart or set the ce pin as "l" and make it "h" again. during the softstart operation of ch1and ch2, the ti mer operates independently fr om the outputs of the error amplifiers. therefore, even if the softstart cannot finish correct ly because of the short circuit, the protection timer function will be able to work correctly. during a timer function, current is restricted by current limit protection or maxduty function until shutdown . normal state short state latch state timer function (typ. 50ms) shutdown a mp output for boost a mp output for invertin g after shutdown drivers and shutdown switch turn off ce v outn 0v discharge hi-z (v outn ) 0v (v outp ) v outp
r1285l 10 inverting dc/dc converter output voltage setting [ r1285l00xb ] the output voltage v outn of the inverting dc/dc converter is controlled with maintaining the v fbn as 0v. v outn can be set with adjusting the values of r1 and r2 as in the next formula. v outn = v fbn - (v ref -v fbn ) x r2 / r1 dc/dc converter?s phase may lose 180 degree by external components of l and c and load current. because of this, the phase margin of the system will be less and the atability will be worse. therefore, the pahse must be gaind. a pole will be formed by external components, l and c. f pole ~ 1 / {2 x x (l2xc2)} zero will be formed with r2 and c4. f zero ~ 1 / (2 x x r2 x c4) set the cutt-off frequency of the zero close to the cutt-off frequency of the pole by l and c. if the noise of the system is large, the output noise affects the feedback and the operation may be unstable. in that case, another resistor r3 will be se t. the appropriate value range is from 1k to 5k . set a ceramic 1 f to 2.2 f capacitor between v ref and gnd as c5. [ r1285l00xb ] operation of step-up dc/dc converter and output current discontinuous mode ilxmax ilxmin ton toff t=1/fosc tf il t ilxmax il ilxmin ton toff t=1/fosc t continuous mode inductor diode cl lx tr v in v out i out il1 il2
r1285l 11 there are two operation modes for the pwm control step- up switching regulator, that is the continuous mode and the discontinuous mode. when the lx tr. is on, the voltage for the inductor l will be vin. the inductor current (il1) will be; il1 = v in x t on / l ............................................................................................................... formula1 when the lx transistor turns off, power will supply continuously. the inducto r current at off (il2) will be; il2 = (v out -v in ) x tf / l .....................................................................................................fo rmula2 in terms of the pwm control, when the tf=toff, the inductor current will be continuous, the operation of the switching regulator will be continuous mode. in the continuous mode, the current vari ation of il1 and il2 are same, therefore v in x t on / l = (v out -v in ) x t off / l ....................................................................................form ula3 in the continuous mode, the duty cycle will be duty = t on / (t on +t off ) = (v out -v in ) / v out ........................................................................form ula4 if the input power equals to output power, i out = v in 2 x t on / (2 x l x v out ) ....................................................................................... formula5 when i out becomes more then formula5, it will be continuous mode. in this moment, the peak current, ilxmax flow ing through the inductor is described as follows: ilxmax = i out x v out / v in + v in x t on /(2 x l) ..................................................................formula6 ilxmax = i out x v out / v in + v in x tx (v out -v in ) /(2 x l x v out ) ....................................... formula7 therefore, peak current is more than i out . considering the value of ilxmax, the condition of input and output, and external components should be selected. the explanation above is based on the ideal calculati on, and the loss caused by lx switch and external components is not included. the actual maximum output current is between 50% and 80% of the calculation. especially, when the il is large, or vin is low, the loss of vin is generated with on resistance of the switch. as for v out , v f (as much as 0.3v)of the diode should be considered. operation of inverting dc/dc converter and output current < basic circuit> inductor diode cl lx tr v in v out i out il1 il2
r1285l 12 there are also two operation modes for the pwm control inverting switching regulator , that is the continuous mode and the discontinuous mode. when the lx tr. is on, the voltage for the inductor l will be vin. the inductor current (il1) will be; il1 = v in x t on / l...................................................................................................................fo rmula8 inverting circuit saves energy during on time of lx tr, and supplies the energy to output during off time, output voltage opposed to input voltage is obtained. the inductor current at off (il2) will be; il2 = v out x tf / l .................................................................................................................fo rmul a9 (the above formula and after, the absolute value of the negative output voltage is assumed to be v out . : output voltage= -10v , v out =10 ) in terms of the pwm control, when the t f =t off , the inductor current will be c ontinuous, the operation of the switching regulator will be continuous mode. in the continuous mode, the current vari ation of il1 and il2 are same, therefore v in x t on / l = v out x t off / l ...................................................................................................formula10 in the continuous mode, the duty cycle will be: duty = t on / (t on +t off ) = v out / (v out + v in )........................................................................fo rmula11 if the input power equals to output power, i out = v in 2 x t on / (2 x l x v out ) .............................................................................................fo rmula12 when i out becomes more then formula12 , it will be continuous mode. in this moment ,the peak current, ilxmax flow ing through the inductor is described as follows: il xmax = i out x v out / v in + v in x t on / (2 x l) ...........................................................................form ula13 il xmax = i out x v out / v in + v in x v out x t / { 2 x l x (v out + v in ) } ......................................... formula14 therefore, peak current is more than i out . considering the value of ilxmax, the condition of input and output, and external components should be selected. the explanation above is based on the ideal calculati on, and the loss caused by lx switch and external components is not included. the actual maximum output current is between 50% and 80% of the calculation. especially, when the il is large, or v in is low, the loss of v in is generated with on resistance of the switch. as for v out , v f (as much as 0.3v)of the diode should be considered. discontinuous mode ilxmax ilxmin ton toff t=1/fosc tf il t ilxmax ilxmin ton toff t=1/fosc t il continuous mode < current through l>

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