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1 ds04-27209-1e fujitsu semiconductor data sheet assp switching regulator controller MB3788 n description the MB3788 is a dual-channel pwm-type switching regulator controller; it in- corporates a reference voltage. the MB3788 has a pwm circuit and an output circuit as well as a reference voltage power supply with a voltage accuracy of 1%. the maximum operating frequency is 1 mhz. it is designed for a voltage-drop output switching regulator suitable for a logic power supply or speed control of a dc motor. the MB3788 is compatible with all master ics producing triangular waves, saw- tooth waves and sine waves with an amplitude of 1.3 to 1.9 v. it can be used in high-performance portable equipment such as a video cam- corder or notebook personal computer (word processor). n features - wide operating power supply voltage range: 3.6 to 18 v - low power dissipation - operating: 1.9 ma (standard) standby: 10 m a max. - high-frequency operation: 100 khz to 1 mhz - on-chip timer and latch-type short-circuit detection circuit - wide error amplifier input voltage range: -0.2 v to v cc - 1.8 v - on-chip high-accuracy reference voltage circuit: 2.50 v 1% - output circuit pnp transistor drive output pin: push-pull type on/off current values set independently - on-chip standby function and output control function - high-density packaging: ssop-24p this device contains circuitry to protect the inputs against damage due to high static voltages or electric fields. however, it is advised that normal precautions be taken to avoid appli- cation of any voltage higher than maximum rated voltages to this high impedance circuit. 24-pin plastic ssop (fpt-24p-m03)
2 MB3788 n pin assignment (top view) v cc (out) out1 ve1 cb1 ca1 fb1 -in1(e) +in1(e) -in1(c) -in(pwn) v cc v ref gnd out2 ve2 cb2 ca2 fb2 -in2(e) +in2(e) -in2(c) scp ctl2 ctl1 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 (fpt-24p-m03)
3 MB3788 n pin description note: the alphabetic characters in parenthesis above indicate the following input pins. (c): comparator (e): error amplifier pin no. pin name i/o descriptions channel 1 2out1o channel 1 push-pull type output 3ve1 i channel 1 output current setting 4ca1 channel 1 output transistor off current setting: output transistor off the current is set by connecting a capacitor between pins ca1 and cb1. 5cb1 6fb1o channel 1 error amplifier output 7-in1(e) i channel 1 error amplifier inversion input 8+in1(e) channel 1 error amplifier non-inversion input 9-in1(c) i channel 1 comparator inversion input channel 2 16 -in2(c) i channel 2 comparator inversion input 17 +in2(e) i channel 2 error amplifier non-inversion input 18 -in2(e) i channel 2 error amplifier inversion input 19 fb2 o channel 2 error amplifier output 20 ca2 channel 2 output transistor off current setting: output transistor off the current is set by connecting a capacitor between pins ca2 and cb2. 21 cb2 22 ve2 i channel 2 output current setting 23 out2 o channel 2 push-pull type output control circuit 13 ctl1 i power and channel 1 control pin h level: power and channel 1 operating l level: standby 14 ctl2 i channel 2 control pin when ctl1 pin = h level, h level: channel 2 operating l level: channel 2 off 15 scp short-circuit protection circuit capacitor connection power circuit 1 v cc 2 output circuit power pin 10 -in(pwm) i master oscillating waveform input 11 v cc1 reference power and control circuit power 12 v ref o reference voltage output 24 gnd ground
4 MB3788 n block diagram 24 channel 1 -in1 (e) fb1 -in1 (c) +in1 (e) 1 2 5 4 ca1 v cc (out) out1 cb1 11 13 14 3 ctl2 v cc ctl1 ve1 10 12 gnd -in(pwm) scp v ref 1.9 v 1.3 v + - + - + - 1.5 v 0.6 v error amplifier 1 comparator 1 pwm comparator 1 off current setting 23 21 20 22 channel 2 -in2 (e) fb2 -in2 (c) +in2 (e) cb2 out2 ca2 ve2 + - + - 1.5 v 0.6 v error amplifier 2 comparator 2 pwm comparator 2 off current setting - - + scp comparator 2.1 v low input voltage protection circuit sr latch circuit reference voltage power (2.5 v) power/channel on/off circuit timer circuit 1 m a v ref + - 15 9 7 6 8 16 18 19 17
5 MB3788 n functional description 1. major functions (1) reference voltage power circuit the reference voltage power supply produces a reference voltage ( ? 2.50 v) which is temperature-compensated by the voltage supplied from the power pin (pin 11); it is used as the ic internal circuit operating power supply. the reference voltage can also be output externally at 1 ma from v ref pin (pin12). (2) error amplifier the error amplifier detects the switching regulator output voltage and outputs a pwm control signal. it has a wide in-phase in put voltage range of -0.2 v to v cc - 1.8 v to make setting from an external power supply easy. connecting the output pin and inversion input pin of the error amplifier through a feedback resistor and capacitor allows setti ng of any loop gain to provide stable phase compensation. (3) pwm comparator the pwm comparator controls the output pulse on time according to the input voltage. the voltage input to the -in pin (pwm) turns the output transistor on when it is lower than the output voltage of the error amp lifier. (4) output circuit the output circuit is configured in a push-pull form and uses a pnp transistor drive system to drive a transistor of up to 30 m a. (see how to set output current. ) 2. channel control function channels can be set on/off by combining the voltage levels at pin ctl1 (pin 13) and pin ctl2 (pin 14). channel on/off setting conditions *the power current in the standby state is 10 m a max. voltage level at ctl pin channel on/off status ctl1 ctl2 power circuit channel 1 channel l stand by state* hh on on loff
6 MB3788 3. protection functions (1) timer and latch-type short-circuit protection circuit the scp comparator detects the output voltage levels of two comparators to detect an output short circuit. if the output volta ge of one comparator increases to 2.1 v, the transistor of the timer circuit is turned off and the short circuit protection capaci tor connected externally to the scp pin (pin 15) starts charging. the latch circuit turns off the output transistor and simultaneously clears the duty cycle to 0 when the output voltage level o f the comparator does not return to the normal voltage level until the capacitor voltage rises to the base-emitter junction voltage v be ( ? 0.65 v) of the transistor. (see how to set time constant for timer & latch-type short-circuit protection circuit. ) when the protection circuit operates, recycle the power to reset the circuit. (2) low input voltage malfunction fail-safe circuit a transient at power-on, or an instantaneous supply voltage drop can cause a control ic malfunction, which may damage the system. the low input voltage malfunction fail-safe circuit detects the internal reference voltage level based on the supply v oltage level, resets the latch circuit, turns off the output transistor, clears the duty cycle to 0 and holds the scp pin (pin 15) at low level. all circuits are recovered when the supply voltage is greater than the threshold voltage of the fail-safe circuit.
7 MB3788 n absolute maximum ratings * value obtained when mounted on 4 cm 4 cm double-sided epoxy substrate n recommended operating conditions (t a = +25 c) parameter symbol conditions ratings unit supply voltage v cc 20 v control input voltage v ictl 20 v allowable loss p d ta +25 c500* mw operating ambient temperature t op -30 to +85 c storage temprature t stg -55 to +125 c (t a = +25 c) parameter symbol conditions values unit min. typical max. supply voltage v cc 3.66.018v reference voltage output curren i or -10ma error amplifier input voltage v i -0.2v cc - 1.8 v error amplifier input voltage v i -0.2v cc v control input voltage v ictl -0.218v output current i o 3.030ma operating frequency f osc 100 300 1000 khz operating ambient temperature t op -30 25 85 c
8 MB3788 n electical characteristics (v cc =6v, t a = +25 c) parameter symbol conditions value unit min. typical max. reference voltage reference voltage v ref i or = -1 ma 2.475 2.500 2.525 v output voltage temperature variation d v ref / v ref t a = -30 to +85 c-2 0.2 2 % input stability line v cc = 3.6 v to 18 v 2 10 mv load stability load i or = -0.1 ma to 1 ma 3 10 mv short-circuit output current i os v ref = 2 v -20 -8 -3 ma low voltage malfunction fail-safe circuit threshold voltage v th 2.65 v v tl 2.45 v hysteresis width v hys 80200mv reset voltage v r 1.51.9v short-circuit detection comparator input offset voltage v io 0.580.650.72v input bias current i ib v i = 0 v -200 -100 na in-phase input voltage range v icm -0.2v cc -1.8 v short-circuit detector threshold voltage v tpc 0.600.650.70v input standby voltage v stb 50100mv input latch voltage v i 50100mv input source current i ibpc -1.4-1.0-0.6 m a error amplifier input offset voltage v io v fb = 1.6 v -10 10 mv input offset current i io v fb = 1.6 v -100 100 na input bias current i ib v fb = 1.6 v -200 -60 na in-phase input voltage range v icm -0.2v cc -1.8 v voltage gain a v 60100db frequency bandwidth bw a v = 0 db 800 khz in-phase signal rejection ratio cmrr 60 80 db maximum output voltage width v om+ v ref -0.3 2.4 v v om- 0.05 0.5 v output sink current i om+ v fb = 1.6 v 120 m a output source current i om- v fb = 1.6 v -2 ma
9 MB3788 parameter symbol conditions values unit min. typical max. pwm comparator threshold voltage v t0 duty cycle = 0 % 1.05 1.3 v v t100 duty cycle = 100 % 1.9 2.25 v input sink current i im+ 120 m a input source current i im- -2ma input bias current i ib v i = 0 v -1.0 -0.5 m a control threshold voltage v th 0.7 1.4 2.1 v input current i ih v ctl = 5 v 100 200 m a i il v ctl = 0 v -10 10 m a output source current i o -40ma sink curren i o r b = 50 w 18 30 42 ma output leak current i lo v o = 18 v 20 m a all devices standby current i cco 010 m a power current at output off i cc 1.92.7ma
10 MB3788 n standard characteristic curves 2.5 2.0 1.5 1.0 0.5 0 048121620 power current l cc (ma) supply voltage v cc (v) 5 4 3 2 1 0 0 4 8 12 16 20 reference voltage v ref ( v) supply voltage v cc (v) ctl1, 2 = 6 v 5 4 3 2 1 0 012345 reference voltage v ref (v) supply voltage v cc (v) v e v ref 2.56 2.54 2.52 2.50 2.48 2.46 2.44 -60 -40 -20 0 20 40 60 80 100 reference voltage v ref (v) ambient temperature t a ( c) 5 4 3 2 1 0 output current setting pin voltage v e (v) v cc = 6 v v ctl1, 2 = 6 v i or = -1 ma 1. power current - supply voltage characteristic 2. reference voltage - supply voltage characteristic 3.reference voltage, output current setting pin voltage - supply voltage characteristic 4. reference voltage - ambient temperature characteristic 3.0 2.8 2.6 2.4 2.2 2.0 012345 reference voltage v ref (v) control voltage vctl1 (v) 500 400 300 200 100 0 048 121620 control current lctl1 ( m a) control voltage v ctl 1 (v) 5. reference voltage - control voltage characteristic 6. control current - control voltage characteristic t a = +25 c t a = +25 c v cc = 6 v t a = +25 c v cc = 6 v t a = +25 c ctl1 = 6 v t a = +25 c
11 MB3788 v cc = 6 v v fb = 1.6 v t a = +25 c 100 80 60 40 20 0 05 k10 k50 k100 k500 k1 m 1.9v 1.3v duty dtr (%) input oscillating frequency (hz) 40 20 0 -20 -40 1 k 10 k100 k1 m5 m10 m t a = +25 c 180 90 0 -90 -180 input waveform gain (db) phase f (deg) 1000 800 600 400 200 0 -20 020 4060 80 100 power dissipation p d (mw) ambient temperature t a ( c) 7. duty - input oscillating frequency characteristic 8.gain - frequency characteristic and phase - frequency characteristic f (hz) 9. power dissipation - ambient temperature characteristic circuit for measuring gain - frequency characteristic and phase - frequency characteristic 2.5 v - + out 2.5 v in + - 10 m f 240 k w 4.7 k w 4.7 k w v cc = 6 v 4.7 k w 4.7 k w error amplifier
12 MB3788 n how to set output voltage + - v ref v out r nf r 1 r 2 r r v out = (r 1 + r 2 ) v ref 2 r 2 note: set the output voltage in the positive range (v out > 0).
13 MB3788 n how to set output current the output circuit is configured in a push-pull type as shown in figure 1. the on current value of the output current waveform shown in figure 2 is a constant current and the off value set by re is set by a time constant. each output current can be calculated from the following expression: on current = 1.5/r e (a) (output current setting pin voltage: v e ? 1.5 v) the off current time constant is proportional to the value of c b . off current setting part r e c b drive tr off current on current output current 0 on current off current t 22 m h (5 v) 3 150 w 1000 pf 4 5 1 v cc i out 1000 pf 10 m f -in1 (e) 8.2 k -in1 (c) MB3788 2 fig.1 output circuit diagram fig.2 output current waveform fig.3 output pin voltage and current waveforms (channel 1) fig.4 measurement circuit diagram v e 2.7 k v out
14 MB3788 n how to set time constant for timer & latch-type short-circuit protection circuit if the load conditions of the switching regulator are stable, the outputs of comparators 1 and 2 do not change, so the sp compa rator outputs a high level. at this time, the scp pin (pin 15) is held at about 50 mv. if the load conditions change suddenly due to a load short-circuit, for example, the output voltage of the comparator of the ch annel becomes a high-level signal (more than 2.1 v). then, the svp comparator outputs a low level and transistor q1 is turned off. the short- circuit protection capacitor c pe externally connected to the scp pin starts to charge. v pe = 50 mv + t pe 10 -6 /c pe 0.65 = 50 mv + t pe 10 -6 /c pe c pe = t pe /0.6 (s) once the capacitor c pe is charged to about 0.65 v, the sr latch is set and the output drive transistor is turned off. at this time, the duty cycle is made low and the output voltage of the scp pin (pin 15) is held at low level. this closes the sr latch input to discharge c pe . fig. 5 latch-type short-circuit protection circuit 2.1 v low input voltage protection circuit sr latch-type circuit 1 m a c pe - - + out 2.5 v 15 q 2 q 1 comparator 1 comparator 2 s r pwm comparator
15 MB3788 n processing without using scp pin if the timer and latch-type short-circuit protection circuit is not used, connect the scp pin (pin 15) to gnd as close as possi ble. also, connect the input pin of each channel comparator to the v cc pin (pin 11). fig. 6 processing without using scp pin 24 9 -in1 (c) v cc 16 -in2 (c) 15 gnd scp 11
16 MB3788 n equivalent series resistance of smoothing capacitor and stability of dc/dc converter the equivalent series resistance (esr) of the smoothing capacity in a dc/dc converter has a great effect on the loop phase char acteristics. the esr causes a small delay at the capacitor with a series resistance of 0 (figures 8 and 9), thus improving system stability. on the other hand, using a smoothing capacitor with a low esr reduces system stability. therefore, attention should be paid to using semico nductor electrolytic capacitors (such as os capacitors) or tantalum capacitors with a low esp. (phase margin reduction by using an os capacitor is e xplained on the next page.) l tr r c r l v in d c 20 0 -20 -40 -60 101001 k 10 k100 k 0 -90 -180 101001 k 10 k100 k (2) (1) (1): r c = 0 w (2): r c = 31 m w (2) (1) gain (db) frequency f (hz) frequency f (hz) phase (deg) (1): r c = 0 w (2): r c = 31 m w fig. 7 basic voltage-drop type dc/dc converter circuit fig.8 gain - frequency characteristic fig.9 phase - frequency charecteristic
17 MB3788 (reference data) the phase margin is halved by changing the smoothing capacitor from an aluminum electrolytic capacitor (rc = 1.0 w ) to a semiconductor electrolytic capacitor (os capacitor: rc = 0.2 w ) with a low esr (figures 11 and 12). fig. 10 dc/dc converter a v - f characteristic meas urement diagram fig. 11 gain - frequency characteristic fig.12 phase - frequency characteristic curves + - a v - f characteristic between v out and v in error amplifier v out c nf fb v in r 2 r 1 v o + - in +in v ref/2 62 a v jt 101001 k 10 k 100 k 60 40 20 0 -20 -40 180 90 0 -90 -180 v cc = 10 v rl = 25 w cp = 0.1 m f gain (db) frequency f (hz) aluminum electrolytic capacitor gain - frequency and phase - frequency characteristics (dc/dc converter +5 v output) aluminum electrolytic capacitor 220 m f (16 v) rc ? 1.0 w : f osc = 1 khz v o + + - phase (deg) gnd a v jt 101001 k 10 k 100 k 60 40 20 0 -20 -40 180 90 0 -90 -180 27 v cc = 10 v rl = 25 w cp = 0.1 m f gain (db) frequency f (hz) os capacitor gain - frequency and phase - frequency characteristics (dc/dc converter +5 v output) os capacitor 22 m f (16 v) rc ? 1.2 w : f osc = 1 khz v o + + - gnd phase (deg)
18 MB3788 n application circuit +15 v +24 v dc motor 1 dc motor 2 24 150 w 23 20 21 22 1000 pf channel 1 (db) (b) 22 m h 3 v 10 m f ca2 cb2 out2 ve2 150 w 1000 pf + (a) 22 m h 5 v 10 m f ca1 v cc (out) out1 ve1 2 3 5 1 4 cb1 (15 ma) channel 2 (deg) 10 m h + - 33 m f + - 33 m f v cc 11 6 9 7 8 -in1 (e) fb1 -in1 (c) +in1 (e) v cc 14 ctl2 13 ctl1 (a) 4.7 k w 4.7 k w 8.2 k w 2.7 k w 100 k w 19 16 18 17 -in2 (e) fb2 -in2 (c) +in2 (e) (b) 4.7 k w 4.7 k w 3.8 k w 2.7 k w 100 k w 15 10 12 gnd -in(pwm) scp v ref y triangular wave signal 1.9 v 1.3 v c t - + - 0.1 m f 0.22 m f 0.22 m f
19 MB3788 n precautions 1. do not apply any voltage greater than the maximum rating, or the lsi may be damaged. 2. use the MB3788 under the recommended operating conditions. if a voltage greater than the maximum voltage is applied, the electrical characteristics are not guaranteed; if a voltage small er than the minimum voltage is applied, the lsi operation will become unstable. 3. to ground the pc board, use the thickest cable possible because high frequencies are used which can easily produce high-frequ ency noise. 4. connecting unused channel pin for unused channels, the output voltage of the comparator for detecting a short-circuit must be fixed at the low level. 5. take measures against static electricity. carry semiconductors in a conductive container or anti-static case. carry the pc board in a conductive bag or container if it is stored or transported after packaging. ground the workbench, and all tools and measuring instruments. workers should be grounded through a resistance of 250 k w to 1 m w .
20 MB3788 n package dimension 24-pin plastic ssop (fpt-24p-m03) dimensions in mm (inches). c 1994 fujitsu limited f24018s-2c-2 0.50?.20 (.020?008) 0.10?.10(.004?004) (stand off) 0 10 details of "a" part 7.75?.10(.305?004) 0.65?.12(.0256?0047) 7.15(.281)ref 6.60(.260) 5.60?.10 nom 7.60?.20 (.220?004) (.299?008) "a" .006 ?001 +.002 ?.02 +0.05 0.15 .049 ?004 +.008 ?.10 +0.20 1.25 .009 ?002 +.004 ?.05 +0.10 0.22 0.10(.004) index * * (mounting height)
MB3788 fujitsu limited f o r fur t her inf o r m ation please contact: japan fujitsu media devices limited marketing and technical support dept. sun hamada bldg 2f 1-19-20, shin-yokohama kouhoku-ku yokohama-shi kanagawa 222-0033, japan tel: 81(45) 471-0061 fax: 81(45) 471-0076 north and south america fujitsu microelectronics, inc. semiconductor division 3545 north first street san jose, ca 95134-1804, usa tel: (408) 922-9000 fax: (408) 922-9179 customer response center mon. - f r i.: 7 am - 5 pm (pst) tel: (800) 866-8608 fax: (408) 922-9179 http://www . fujitsumicro . com/ europe fujitsu mikroelektronik gmbh am siebenstein 6-10 d-63303 dreieich-buchschlag germany tel: (06103) 690-0 fax: (06103) 690-122 http://www . fujitsu-ede .com/ asia pacific fujitsu microelectronics asia pte ltd #05-08, 151 lorong chuan new tech park singapore 556741 tel: (65) 281-0770 fax: (65) 281-0220 http://www . fmap .com.sg/ f9902 ? fujitsu limited printed in japan all rights reserved. the contents of this document are subject to change without notice. customers are advised to consult with fujitsu sales representatives before ordering. the information and circuit diagrams in this document are presented as examples of semiconductor device applications, and are not intended to be incorporated in devices for actual use. also, fujitsu is unable to assume responsibility for infringement of any patent rights or other rights of third parties arising from the use of this information or circuit diagrams. fujitsu semiconductor devices are intended for use in standard applications (computers, office automation and other office equipment, industrial, communications, and measurement equipment, personal or household devices, etc.). caution: customers considering the use of our products in special applications where failure or abnormal operation may directly affect human lives or cause physical injury or property damage, or where extremely high levels of reliability are demanded (such as aerospace systems, atomic energy controls, sea floor repeaters, vehicle operating controls, medical devices for life support, etc.) are requested to consult with fujitsu sales representatives before such use. the company will not be responsible for damages arising from such use without prior approval. any semiconductor devices have an inherent chance of failure. you must protect against injury, damage or loss from such failures by incorporating safety design measures into your facility and equipment such as redundancy, fire protection, and prevention of over-current levels and other abnormal operating conditions. if any products described in this document represent goods or technologies subject to certain restrictions on export under the foreign exchange and foreign trade law of japan, the prior authorization by japanese government will be required for export of those products from japan.

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