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1 data sheet ud200541 june 9, 2005 v7 synchronous step-down dc/dc converter with built-in ldo regulator plus voltage detector step-down dc/dc converter's output connected in series with ldo regulator high efficiency, low noise regulated output ultra small packages: msop-10, usp-10 small-footprint output current dc/dc:600ma, vr: 200ma ceramic capacitor compatib le (low esr capacitors) general description the xc9508 series consists of a step-down dc/dc converter and a high-speed ldo regulator connected in series with the dc/dc converter's output. a voltage detector is also built-in. a highl y efficient, low noise output is possibl e since the regulator is stepped-down further from the dc/dc output. the dc/dc converter block incorpor ates a p-channel driver transisto r and a synchronous n-channel switching transistor. with an external coil, diode and two capacitors, the xc9508 can deliver output currents up to 600ma at efficiencies over 90%. the xc9508 is designed for use with small ceramic capacitors. a choice of three switching frequencies are available, 300 khz, 600 khz, and 1.2 mhz. output voltage settings for the dc/dc is set-up internally in 100mv steps within the range of 1.6v to 4.0v( 2.0%) and for the vr are set-up internally within the range of 0.9v to 4.0v ( 2.0%). for the vd, the range is of 0.9v to 5.0v ( 2.0%). the soft start time of the series is internally set to 5ms. with the built-in u.v.l.o. (under voltage lock out) function, the internal p-channel drive r transistor is forced off when input voltage becomes 1.4 v or lower. the functions of the mode pin can be selected via the external control pin to switch the dc/dc control mode and the disable pin to shut down the regulator block. a pplications cd-r / rw, dvd hdd pdas, portable communication modem cellular phones palmtop computers cameras, video recorders typical application circuit features input voltage range : 2.4v ~ 6.0v low esr capacitor : ceramic capacitor compatible vd function : n-channel open drain output output voltage range : 1.6v ~ 4.0v (accuracy 2%) output current : 600ma (for msop-10 package) 400ma (for usp-10 package) controls : pwm control pwm, pwm/pfm automatic switching external oscillation frequency : 300khz, 600khz, 1.2mhz output voltage range : 0.9v ~ 4.0v (accuracy 2%) current limit : 300ma dropout voltage : 80mv @ iout=100ma (vout=2.8v) high ripple rejection : 60db @1khz (vout=2.8v) typical performance characteristics x c9508cxxxx v in =3.6v, topr=25 o c l=4.7 h (cdrh4d28c) c in :4.7
2 xc9508 series data shee t ud200541 designator description symbol description control methods and the vd sense pin as chart below : - ? setting voltage & specifications internal standard : setting voltage and specifications of each dc/dc, vr, and vd (based on the internal standard) 3 : 300khz 6 : 600khz dc/dc oscillation frequency c : 1.2mhz a : msop-10, current limiter: 1.1a (typ.) package & dc/dc current limit d : usp-10, current limiter: 0.7a (typ.) r : embossed tape, standard feed device orientation l : embossed tape, reverse feed series dc/dc control methods mode pins (h level) mode pins (l level) a pwm control vr: off vr: on xc9508 c pwm, pfm/pwm manual switch pfm / pwm switch pwm control pin number pin name function 1 pgnd power ground 2 ce chip enable 3 v dd power supply 4 v dout vd output 5 v din vd input 6 agnd analog ground 7 mode mode switch 8 v rout vr output 9 d cout dc/dc output sense 10 lx switch pin configuration pin assignment product classification ordering information xc9508 ????? the input for the voltage regulator block comes from the dc/dc. pgnd 1 ce 2 vdd 3 vdout 4 vdin 5 10 lx 9 dcout 8 vrout 7 mode 6 agnd *please use the circui t without connecting the heat dissipation pad. if the pad needs to be connected to other pins, it should be connected to the agnd p in. usp-10 (bottom view) control methods and mode pin * the xc9508a series' mode pin switches the regulator to the stand-by mode. when the ce mode is off, every func tion except for the vd function enters into the stand-by mode. (the mode pin does not operate independently.) msop-10 (top view)
3 data sheet ud200541 x c9508 series mark product series 7 xc9508xxxxxx mark dc/dc control mode pin (h level) mode pin (l level) product series a pwm control vr:off vr:on xc9508axxxxx c pwm, pfm/pwm manual switching pfm/pwm a uto switching pwm control xc9508cxxxxx s custom xc9508cxxxxx mark dc/dc vr vd product series 1 5 2.0v 1.5v 1. 9v XC9508X15XXX mark oscillation frequency product series 3 300khz xc9508xxx3xx 6 600khz xc9508xxx6xx c 1.2mhz xc9508xxxcxx marking rule msop-10, usp-10 represents product series represents dc/dc control methods and mode pin represents production lot number 0 to 9, a to z reverse character 0 to 9, a to z repeated (g, i, j, o, q, w excepted) note: no character inversion used. packaging information msop-10 usp-10 * soldering fillet surface is no t formed because the sides o f the pins are not plated. ? represents detect voltage dc/dc,vr and vd. ex) represents oscillation frequency usp-10 (top view) msop-10 (top view) 0.15+0.08 0.53+0.13 3.00+0.10 3.00+0.10 4.90+0.20 0 ~ 6 o 0.20 +0.1 -0.05 (0.5) 0.86+0.15 0~0.15 1 1 1 1 1 1 1
4 xc9508 series data shee t ud200541 parameter symbol ratings unit v dd pin voltage v dd - 0.3 ~ 6.5 v d cout pin voltage d cout - 0.3 ~ v dd + 0.3 v v rout pin voltage v rout - 0.3 ~ v dd + 0.3 v v rout pin current i rout 800 ma v dout pin voltage v dout - 0.3 ~ v dd + 0.3 v v dout pin current i vd 50 ma v din pin voltage v din - 0.3 ~ v dd + 0.3 v lx pin voltage lx - 0.3 ~ v dd + 0.3 v msop-10 1300 lx pin current usp-10 ilx 900 ma ce pin voltage ce - 0.3 ~ vdd + 0.3 v mode pin voltage mode - 0.3 ~ vdd + 0.3 v msop-10 350 (*) power dissipation usp-10 pd 150 mw operating temperature range topr - 40 ~ + 85 storage temperature range tstg - 55 ~ + 125 block diagram a bsolute maximum ratings * diodes shown in the above circuit are p rotective diodes ta = 2 5 (*) when pc board mounted.
5 data sheet ud200541 x c9508 series parameter symbol conditions min. typ. max. units circuit supply current 1 i dd 1 v in =ce=d cout =5.0v - 250 310 a 1 supply current 2 i dd 2 v in =ce=5.0v, d cout =0v - 300 360 a 1 stand-by current (*1) i stb v in =6.5v, ce=0v - 0.5 2.5 a 1 input voltage range v in 2.4 - 6.0 v - ce ?h? level voltage v ceh 0.6 - v dd v 3 ce ?l? level voltage v cel v ss - 0.25 v 3 ce ?h? level current i ceh - 0.1 - 0.1 a 1 ce ?l? level current i cel - 0.1 - 0.1 a 1 mode 'h' level voltage *xc9508a vmh 0.6 - v dd v 2 mode 'h' level voltage *xc9508c vmh 0.6 - v dd v 3 mode 'l' level voltage *xc9508a vml v ss - 0.25 v 2 mode 'l' level voltage *xc9508c vml v ss - 0.25 v 3 mode 'h' level current imh - 0.1 - 0.1 a 1 mode 'l' level current iml - 0.1 - 0.1 a 1 parameter symbol conditions min. typ. max. units circuit supply current 1 *xc9508a i dd _dc1 v in =ce=d cout =5.0v - 200 280 a 1 supply current 2 *xc9508a i dd _dc2 vi n =ce=5.0v, d cout =0v 250 330 a 1 pfm supply current 1 * 9508c i dd _pfm1 v in =ce=d cout =5.0v 250 310 a 1 pfm supply current 2 * 9508c i dd _pfm2 v in =ce=5.0v, d cout =0v 300 360 a 1 output voltage dc out (e) connected to the external components, i dout =30ma 2.156 2.200 2.244 v 3 oscillation frequency f osc connected to the external components, i dout =10ma 1.02 1.20 1.38 mhz 3 maximum duty ratio maxduty d cout =0v 100 - - % 4 minimum duty ratio minduty d cout =v in - - 0 % 4 pfm duty ratio pfmduty connected to the external components, no load 21 30 38 % 3 u.v.l.o. voltage (*2) vuvlo connected to the external components 1.00 1.40 1.78 v 3 lx sw ?high? on resistance (*3) rlxh d cout =0v, lx=v in -0.05v - 0.5 0.9 5 lx sw ?low? on resistance rlxl connected to the external components, v in =5.0v - 0.5 0.9 3 lx sw ?high? leak current (*12) ileakh v in =lx=6.0v, ce=0v - 0.05 1.00 a 11 lx sw ?low? leak current (*12) ileakl v in =6.0v, lx=ce=0v - 0.05 1.00 a 11 maximum output current imax1 connected to the external components 600 - - ma 3 current limit (*9) ilim1 1.0 1.1 - a 6 efficiency (*4) effi connected to the external components, i dout =100ma - 90 - % 3 output voltage i dout =30ma temperature characteristics u dc out ( u topr ? d cout ) -40 Q topr Q 85 - 100 - ppm/ 3 soft-start time tss connected to the external components, ce=0v t v in , i dout =1ma 2 5 10 ms 3 latch time (*5, 10) tlat connected to the external components, v in =ce=5.0v, short d cout by 1 resistor - 8 25 ms 10 electrical characteristics xc9508xxxcax common characteristics topr=25 dc/dc converter (2.2v product) topr=25
6 xc9508 series data shee t ud200541 parameter symbol conditions min. typ. max. units circuit output voltage vr out (e) ir out =30ma 1.764 1.800 1.836 v 2 maximum output current imax2 200 - - ma 2 load regulation u vr out 1ma Q ir out Q 100ma - 15 50 mv 2 dropout voltage 1 (*6) vdif 1 ir out =30ma - 30 200 mv 2 dropout voltage 2 vdif 2 ir out =100ma - 100 200 mv 2 line regulation u vrout u v in ? vr out ir out =30ma vr out (t)+1v Q v in Q 6v - 0.05 0.25 %/v 2 current limit ilim2 vr out =vr out (e) x 0.9 240 300 - ma 7 short-circuit current ishort vr out =vss - 30 - ma 7 ripple rejection rate psrr v in ={v out (t)+1.0} v dc +0.5vp-pac, ir out =30ma, f=1khz - 60 - db 12 output voltage temperature characteristics u vr out u to p r ? vr out ir out =30ma -40 Q topr Q 85 - 100 - ppm/ 2 parameter symbol conditions min. typ. max. units circuit detect voltage v df (e) ce=0v 2.646 2.700 2.754 v 8 hysteresis range v hys v hys =[v dr (e) (*11) - v df (e)] / v df (e) x 100 2 5 8 % 8 vd output current i vd vd out =0.5v, ce=0v 1 - - ma 9 output voltage temperature characteristics u v df u to p r ? vdf -40 Q topr Q 85 - 100 - ppm/ 8 xc9508xxxcax (continued) regulator (1.8v product) topr=25 detector (2.7v product) test conditions: unless otherwise stated: dc/dc : v in =3.6v [@ dc out :2.2v] vr: v in = 2.8v (v in =vr out (t) + 1.0v) vd: v in =5.0v common conditions for all test items: ce=v in , mode=0v * vr out (t) : setting output voltage note: *1 : including vd supply current (vd operates when in stand-by mode.) *2 : including hysteresis operating voltage range. *3 : on resistance ( )= 0.05 (v) / ilx (a) *4 : effi = { ( output voltage x output current ) / ( input voltage x input current) } x 100 *5 : time until it short-circuits dc out with gnd through 1 of resistance from a state of operation and is set to dc out =0v from current limit pulse generating. *6 : vdif = (v in 1 ( * 7) - vr out 1 ( * 8) ) *7 : v in 1 = the input voltage when vr out 1 appears as input voltage is gradually decreased. *8 : vr out 1 = a voltage equal to 98% of the output voltage whenever an amply stabilized i out {vr out (t) + 1.0v} is input. *9 : current limit = when v in is low, limit current may not be reached because of voltage falls caused by on resistance or serial resistance of coils. *10: integral latch circuit=latch time may bec ome longer and latch operation may not work when v in is 3.0v or more. *11: v dr (e) = vd release voltage *12: when temperature is high, a current of approximately 5.0 a (maximum) may leak. electrical characteristics (continued)
7 data sheet ud200541 x c9508 series test circuits output voltage (dc/dc) oscillation frequency, uvlo voltage, soft-start time, ce voltage, maximum output current, efficiency, (pfm duty cycle), (mode voltage) circuit 3 minimum duty cycle, maximum duty cycle circuit 4 circuit 1 supply current, stand-by current, ce current, mode current circuit 2 output voltage (vr), load regulation, dropout voltage, maximum output current, (mode voltage) circuit 5 lx on resistance circuit 6 current limit 1 (dc/dc)
8 xc9508 series data shee t ud200541 test circuits ( continued ) circuit 7 current limit 2 (vr), short circuit current (vr) circuit 8 detect voltage, release voltage (hysteresis range) circuit 9 vd output current circuit 10 latch time circuit 12 ripple rejection rate circuit 11 off-leak
9 data sheet ud200541 x c9508 series fosc l 1.2mhz 4.7 h (cdrh4d28c, sumida) 600khz 10 h (cdrh5d28, sumida) 300khz 22 h (cdrh6d28, sumida) cin cl1 cl2 (*2) vr out Q 2.0v 4.7 f (ceramic, taiyo yuden) vdif 1.0v 1.0 f (ceramic, taiyo yuden) 4.7 f (ceramic, taiyo yuden) 10 f (ceramic, taiyo yuden) vr out 2.0v vdif Q 1.0v 4.7 f (ceramic, taiyo yuden) typical application circuit msop-10 (top view) *1 the dc/dc converter of the xc9508 series automatically switches between synchronous / non-synchronous. the schottky diode is not normally needed. however, in cases where high ef ficiency is required when using the dc/dc converter during in the light load while in non-synchronous operati on, please connect a scho ttky diode externally. *2 please be noted that the recommend value above of t he cl2 may be changed depending on the input voltage value and setting voltage value. operational explanation the xc9508 series consists of a synchronous step-down dc/ dc converter, a high speed ldo voltage regulator, and a voltage detector. since the ldo voltage regulator is steppe d-down from the dc/dc's output, high efficiency and low noise is possible even at lower output voltages. dc/dc converter the series consists of a reference voltage source, ramp wave circuit, error amplifier, pwm comparator, phase compensation circuit, output voltage adjustment resistors, dr iver transistor, synchronous switch, current limiter circuit, u.v.l.o. circuit and others. the series ics compare, using the error amplifier, the volt age of the internal voltage reference source with the feedback voltage from the v out pin through split resistors. phase compensation is performed on the resulting error amplifier output, to input a signal to the pwm comparator to determine the turn-on time during pwm operation. the pwm comparator compares, in te rms of voltage level, the signal from the error amplifie r with the ramp wave from the ramp wave circuit, and delivers t he resulting output to the buffer driver circuit to cause the lx pin to output a switching duty cycle. this process is continuously performed to ensure stable output voltage. the current feedback circuit monitors the p-channel mos driv er transistor current for each switching operation, and modulates the error amplifier output signal to provide mult iple feedback signals. this enables a stable feedback loop even when a low esr capacitor, such as a ceramic capacitor, is used, ensuring stable output voltage. the reference voltage source provides the reference voltag e to ensure stable output vo ltage of the dc/dc converter. the ramp wave circuit determines switching frequency. the frequency is fixed internally and can be selected from 300khz, 600 khz and 1.2 mhz. clock pulses generated in th is circuit are used to produce ramp waveforms needed for pwm operation, and to synchronize all the internal circuits. the error amplifier is designed to monitor output voltage. the amplifier compares the reference voltage with the feedback voltage divided by the internal split resistors. when a voltage lower than the reference voltage is fed back, the output voltage of the erro r amplifier increases. the gain and frequency c haracteristics of the error amplifier output are fixed internally to deliver an optimized signal to the mixer. sd *1 : xb0asb03a1br (torex)
10 xc9508 series data shee t ud200541 dc/dc converter (continued) the xc9508a series is pwm control, while the xc9508c se ries can be automatically switched between pwm control and pwm/pfm control. the pwm of the xc 9508a series is controlled on a specif ied frequency from light loads through the heavy loads. since the frequency is specified, the composition of a noise filter etc. bec omes easy. however, the efficiency at the time of the light load may become low. the xc9508c series can switch in any timing between pw m control and pwm/pfm automatic switching control. the series cannot control only pfm mode. if needed, the operation can be set on a specified frequency; therefore, the control of the noise etc. is possible and the high efficiency at the time of the light load during pfm control mode is possible. with the automatic pwm/pf m switching control function, the seri es ics are automatically switched from pwm control to pfm control mode under light load conditio ns. if during light load conditions the coil current becomes discontinuous and on-time rate falls lowe r than 30%, the pfm circuit operates to output a pulse with 30% of a fixed on-time rate from the lx pin. during pfm operation with this fixed on-time rate, pulses are generated at differen t frequencies according to conditions of the moment. this c auses a reduction in the number of switching operations pe r unit of time, resulting in efficiency improvement under light load conditions. however, since pulse output frequency is not constant, consideration should be given if a noise filter or the like is needed. necessary conditions for switching to pfm operation depend on input voltage, load current, coil value and other factors. the xc9508 series automatically switches between synchrono us / non-synchronous accordi ng to the state of the dc/dc converter. highly efficient operations are achievable us ing the synchronous mode while the coil current is in a continuous state. the series enter s non-synchronous operation when the built-in n-ch switching transistor fo r synchronous operation is shutdown, which happens when t he load current becomes low and the operation changes to a discontinuous state. the ic can operate without an extern al schottky diode because the parasitic diode in the n-ch switching transistor provides the circuit's step-down operation. however, since vf of the parasitic diode is a high 0.6v, the efficiency level during non-synchronous operation shows a slight decrease. please use an external schottky diode if high efficiency is required during light load current. continuous mode: synchronous discontinuous mode: non-synchronous operational explanation ( continued )
11 data sheet ud200541 x c9508 series dc/dc converter (continued) the current limiter circuit of the xc9508 series monitors the current flow ing through the p-channel mos driver transisto r connected to the lx pin, and features a combination of t he constant-current type current limit mode and the operation suspension mode. when the driver current is greater than a specific level, the c onstant-current type current limit function operates to turn off the pulses from the lx pin at any given timing. when the driver transistor is turned off, the limiter circui t is then released from the current limit detection state. at the next pulse, the driver transistor is turned on. howe ver, the transistor is immediately turned off in the case o f an over current state. when the over current state is eliminat ed, the ic resumes its normal operation. the ic waits for the over current state to end by repeating the steps through . if an over current state continues for 8msec* and the above three steps are repeatedl y performed, the ic performs the function of latching the off state of the driver transistor, and goes into operation suspension mode. once the ic is in suspension mode, operations can be resumed by eit her turning the ic off via the ce/mode pin, or by restoring power to the v in pin. the suspension mode does not mean a complete sh utdown, but a state in which pulse output is suspended; therefore, the internal circuitry remain s in operation. the constant-current type current limit of the xc9508 series can be set at 1.1a for msop-10 package and 0.7a for usp-10 package when the v in pin voltage becomes 1.4 v or lower, the p-channel out put driver transistor is forced off to prevent false pulse output caused by unstable operation of the internal circuitry. when the v in pin voltage becomes 1.8 v or higher, switching operation takes place. by re leasing the u.v.l.o. function, the ic performs the soft start function to initiate output startup operation. the soft st art function operates even when the v in pin voltage falls momentarily below the u.v.l.o. operating voltage. the u.v.l.o. circuit does not cause a complete sh utdown of the ic, but causes pulse output to be suspended; ther efore, the internal circuitry remains in operation. high speed ldo voltage regulator the voltage regulator block of the xc9508 series consists of a reference voltage source, error amplifier, and current limiter circuit. the voltage divided by split resistors is compared with the internal reference voltage by the erro r amplifier. the p-channel mosfet, which is connected to the vr out pin, is then driven by the subsequent output signal. the output voltage at the vrou t pin is controlled and stabilized by a system of negative feedback. a stable output voltage is achievable even if used with low esr ca pacitors as a phase compensation circuit is built-in. the reference voltage source provides the reference volt age to ensure stable output voltage of the regulator. the error amplifier compares the reference voltage with the signal from vr out , and the amplifier controls the output o f the pch driver transistor. the voltage regulator block includes a co mbination of a constant cu rrent limiter circuit and a foldback circuit. when the load current reaches the current limit le vel, the current limiter circuit operates and the output voltage of the voltage regulator block drops. as a result of this drop in output voltage, the fold back circuit operates, output voltage drops further and the load current decreases. when the vr out and gnd pin are shor ted, the load current of about 30ma flows. operational explanation ( continued )
12 xc9508 series data shee t ud200541 dc/dc waveform (3.3v, 1.2mhz) < external components> l:4.7 h(cdrh4d28c,sumida) cin:4.7 f(ceramic) cl:10 f(ceramic) < external components> l:4.7 h(cdrh4d28c,sumida) cin:4.7 f(ceramic) cl:10 f(ceramic) voltage detector the detector block of the xc9508 seri es detects output voltage from the vd out pin to the signal, which enters from vd in . (n-channel open drain type) the operation of the xc9508 series' dc/ dc converter block and voltage regulator block will enter into the shut down mode when a low level signal is input to the ce pin. during the shut down mode, the current consumption occurs only in the detector and is 0.6 a (typ.), with a state of hi gh impedance at the lx pin and dc out pin. the ic starts its operation by inputting a high level signal to the ce pin. the input to the ce pin is a cmos input and the sink current is 0 a (typ.). the operation of the xc9508a series' voltage detector block will enter into stand-by mode when a high level signal is input to the mode pin. when a low level signal is input, the voltage regulator block will enter into stand-by mode. however, if the ic enters into stand-by mode via the ce pin, the voltage regulator block also shuts down. with the xc9508c series control can be pwm control when the mode pin is 'h' level and pwm/pfm automatic switching control when the mode pin is 'l' level. application information 1. the xc9508 series is designed for use with ceramic out put capacitors. if, however, the potential difference between dropout voltage or output curr ent is too large, a ceramic capacitor may fail to absorb the resulting high switching energy and oscillation could occur on the output. if the input-output potential difference is large, connect an electrolytic capacitor in parallel to compensate for insufficient capacitance. 2. spike noise and ripple voltage arise in a switch ing regulator as with a dc/dc converter. these are greatl y influenced by external component selection, such as the coil inductance, capacitance values, and board layout o f external components. once the design has been completed, verification with actual components should be done. 3. when the difference between v in and v out is large in pwm control, very narrow pulses will be outputted, and there is the possibility that some c ycles may be skipped completely. 4. when the difference between v in and v out is small, and the load current is heav y, very wide pulses will be outputted and there is the possibility that some cycles may be skipped completely: in this case, the lx pin may not go low at all. notes on use operational explanation ( continued )
13 data sheet ud200541 x c9508 series dc/dc waveform (1.8v, 600khz) @ vin=6.0v < external components> l:10 h(cdrh5d28c,sumida) cin:4.7 f(ceramic) cl:10 f(ceramic) step down ratio:1.8v / 6.0v=30% application information (continued) 5. the ic's dc/dc converter operates in synchronous m ode when the coil current is in a continuous state and non-synchronous mode when the coil current is in a discontin uous state. in order to maintain the load current value when synchronous switches to non-synchronous and vi se versa, a ripple voltage may increase because of the repetition of switching between synchr onous and non-synchronous. when this state continues, the increase in the ripple voltage stops. to reduce the ripple voltage, pl ease increase the load capacitance value or use a schottk y diode externally. when the current used becomes close to the value of the load current when synchronous switches to non- synchronous and vise versa, the swit ching current value can be changed by changing the coil inductance value. in case changes to coil inductance are to values other than the recommended coil inductance values, verification with actual components should be done. ics = (v in - dc out ) x onduty / (l x fosc) ics: switching current from synchronous rectification to non-sync hronous rectification onduty: onduty ratio of p-ch driver transistor ( . =.step down ratio : dc out / v in ) l: coil inductance value fosc: oscillation frequency id out : the dc/dc load current (the sum of the dc/dc's and t he regulator's load if the regulator has load.) 6. when the xc9508c series operates in pwm/pfm auto matic switching control mode, the reverse current may become quite high around the load current value when sync hronous switches to non-synchronous and vise versa (also refer to no. 5 above). under this condition, sw itching synchronous rectific ation and non-synchronous rectification may be repeated because of the reverse current, and the ripple voltage may be increased to 100mv o r more. the reverse current is the current that flows in the pgnd direction through the n-ch driver transistor from the coil. the conditions, which caus e this operation, are as follows. pfm duty step down ratio = dc out / v in 100 (%) pfm duty: 30% (typ.) please switch to pwm control via the mode function in cases where the lo ad current value of the dc/dc converte r is close to synchronous . notes on use ( continued )
14 xc9508 series data shee t ud200541 application information (continued) 7. with the dc/dc converter of the ic, the peak current of the coil is controlled by the current limit circuit. since the peak current increases when dropout voltag e or load current is high, current limit starts operating, and this can lead to instability. when peak current becomes high, please ad just the coil inductance value and fully check the circuit operation. in addition, please calculate the peak current according to the following formula: peak current: ipk = (vin - dc out ) onduty / (2 l fosc) + id out 8. when the peak current, which exceeds limit current flows within the specified time, the built-in driver transistor is turned off (the integral latch circuit). during the time until it detects limit current and befo re the built-in transistor can be turned off, the current for limit current flows; therefore, care must be tak en when selecting the rating for the coil o r the schottky diode. 9. when v in is low, limit current may not be reached because of voltage falls caused by on resistance or serial resistance of the coil. 10. in the integral latch circuit, latch time may become longer and latch operation may not work when vin is 3.0v o r more. 11. use of the ic at voltages below the recommended voltage range may lead to instability. 12. this ic and the external components should be used with in the stated absolute maximum ratings in order to prevent damage to the device. 13. since the dc/dc converter and the regulator of the xc9508 series are connected in series, the sum of the output current (id out ) of the dc/dc and the output current (ir out ) of the vr makes the current flows inside the dc/dc converter. please be careful of the power dissipation when in use. please calculate power dissipation by using the following formula. pd=pddc/dc + pdvr dc/dc power dissipation (when in synchronous operation) : pddc/dc = id out 2 ron vr power dissipation: pdvr=(dc out ? vr out ) ir out ron: on resistance of the built-in driver transistor to the dc/dc (= 0.5 ) ron=rpon p-chonduty / 100 + rnon (1 ? p-chonduty / 100) 14. the voltage detector circuit built-in the xc9508 series internally monitor the v dd pin voltage, the dc/dc output pin voltage and vr output pin voltage. pleas e determine the detect voltage value (v df ) by the following equation. vdf Q (setting voltage on both the dc out voltage and the vr out voltage) 85%* * an assumed value of tolerance among the dc out voltage, the vr out voltage, and the vd release voltage (the vd detect voltage and hysteresis range). notes on use ( continued )
15 data sheet ud200541 x c9508 series instructions on pattern layout 1. in order to stabilize v in' s voltage level, we recommend that a by-pass capacitor (c in ) be connected as close as possible to the v dd & agnd pins. this ic is the composite ic of the dc/dc converter and regulator. fluctuation of the v in 's voltage level causes mutual interference. 2. please mount each external component as close to the ic as possible. 3. wire external components as close to the ic as possi ble and use thick, short connecting traces to reduce the circuit impedance. 4. make sure that the pcb gnd traces are as thick as possible, as variati ons in ground potential caused by high ground currents at the time of switching may result in instability of the dc/dc converte r and have adverse influence on the regulator output. 5. if using a schottky diode, please connect the anode side to the agnd pin through c in . characteristic degradation caused by the noise may occur depending on the arrangement of the schottky diode. + + + ic l sd vin pgnd lx agnd vrout dcout ce mode vdin vdout ( through hole to sd ) cin cl2 cl1 notes on use ( continued )
16 xc9508 series data shee t ud200541 typical performance characteristics (a) dc/dc converter (1) efficiency vs. output current
17 data sheet ud200541 x c9508 series (2) output voltage vs. output current typical performance characteristics (continued) (a) dc/dc converter (continued)
18 xc9508 series data shee t ud200541 (3) output voltage vs. ripple voltage typical performance characteristics (continued) (a) dc/dc converter (continued)
19 data sheet ud200541 x c9508 series (4) output voltage vs. ambient temperature (5) soft start time vs. ambient temperature typical performance characteristics (continued) (a) dc/dc converter (continued)
20 xc9508 series data shee t ud200541 (6) dc/dc supply current vs. ambient temperature (vr: shutdown)* typical performance characteristics (continued) (a) dc/dc converter (continued)
21 data sheet ud200541 x c9508 series (7) lx pch/nch on resistance vs. input voltage (8) oscillation frequency vs. ambient temperature (9) u.v.l.o. voltage vs. ambient temperature typical performance characteristics (continued) (a) dc/dc converter (continued)
22 xc9508 series data shee t ud200541 (10-1) dc/dc load transient respo nse (dcout:1.8v, fosc:1.2mhz) (a)pwm control (10-1) dc/dc load transient response (dcout: 1.8v, fosc: 1.2mhz) (a) pwm control ( b ) pwm/pfm automatic switchin g control* ( *xc9508c series onl y) typical performance characteristics (continued) (a) dc/dc converter (continued)
23 data sheet ud200541 x c9508 series (10-2) dc/dc load transient response (*dcout: 3.3v, fosc: 1.2mhz) (a) pwm control (b) pwm/pfm automatic switching control* (*xc9508c series only) typical performance characteristics (continued) (a) dc/dc converter (continued)
24 xc9508 series data shee t ud200541 (10-3) dc/dc load transient response (*dcout: 1.8v, fosc: 600khz) (a) pwm control (b) pwm/pfm automatic switching control* (*xc9508c series only) typical performance characteristics (continued) (a) dc/dc converter (continued)
25 data sheet ud200541 x c9508 series (b)pwm/pfm automatic switching control* (*xc9508c series only) (10-4) dc/dc load transient response (*dcout: 3.3v, fosc: 600khz) (a) pwm control typical performance characteristics (continued) (a) dc/dc converter (continued)
26 xc9508 series data shee t ud200541 (1) output voltage vs . input voltage (b) voltagre regulator typical performance characteristics (continued)
27 data sheet ud200541 x c9508 series (2) output voltage vs . output current (current limit) typical performance characteristics (continued) (b) voltagre regulator (continued)
28 xc9508 series data shee t ud200541 (3) dropout voltage vs . output current typical performance characteristics (continued) (b) voltagre regulator (continued)
29 data sheet ud200541 x c9508 series (4) output voltage vs . output current typical performance characteristics (continued) (b) voltagre regulator (continued)
30 xc9508 series data shee t ud200541 (5) output voltage vs . ambient temperature typic a l performance characteristics (continued) (b) voltagre regulator (continued)
31 data sheet ud200541 x c9508 series (6) ripple rejection ratio vs . ripple frequency typical performance characteristics (continued) (b) voltagre regulator (continued)
32 xc9508 series data shee t ud200541 (7) vr load transient response typical performance characteristics (continued) (b) voltagre regulator (continued)
33 data sheet ud200541 x c9508 series (c) voltage detector (1) output current vs. input voltage (2) detect voltage vs. input voltage typical performance char a cteristics (continued)
34 xc9508 series data shee t ud200541 (3) detect voltage, release voltage vs. ambient temperature typical performance characteristics (continued) (c) voltage detector (continued)
35 data sheet ud200541 x c9508 series (d) common (1) supply current vs. ambient temperature (dc/dc & vr & vd) (2) shutdown current vs. input voltage (3) shutdown current vs. ambient temperature typical performance characteristics (continued)
36 xc9508 series data shee t ud200541 (4) ce pin threshold voltage vs. ambient temperature (5) mode pin threshold voltage vs. ambient temperature typical performance characteristics (continued) (d) common (continued) a mbient temperature : ta ( ) a mbient temperature : ta ( )

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