Instruction/ maintenance manual of the product MB3788 Fujitsu
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DS04-27209-3E FUJITSU SEMICONDUCT OR DA T A S H E E T ASSP SWITCHING REGULA T OR CONTR OLLER MB3788 ■ ■ ■ ■ DESCRIPTION The MB3788 is a dual-channel PWM-type s witching regulator controller ; it incor por ates a ref erence voltage .
MB3788 2 (Continued) • High-frequency operation: 100 kHz to 1 MHz • On-chip timer and latch-type shor t-circuit detection circuit • Wide error amplifier input v oltage range: -0.2 V to V CC - 1.8 V • On-chip high-accuracy ref erence v oltage circuit: 2.
MB3788 3 ■ ■ ■ ■ PIN DESCRIPTION Note: The alphabetic characters in parenthesis abo ve indicate the f ollowing input pins. (C): Comparator (E): Error amplifier Pin No.
MB3788 4 ■ ■ ■ ■ BLOCK DIA GRAM 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.
MB3788 5 ■ ■ ■ ■ FUNCTIONAL DESCRIPTION 1. Major Functions (1) Reference v oltage power cir cuit The ref erence voltage po wer supply produces a ref e rence v oltage ( ≈ 2.50 V) which is temperature-compensated by the v oltage supplied from the pow er pin (pin 11); it is used as the IC intern al circuit operating po wer supply .
MB3788 6 3. Pr otection Functions (1) Timer and latch-type short-circuit pr otection circuit The SCP comparator detects the output v oltage lev els of two comparators to detect an output short circuit. If the output v oltage of one comparator increases to 2.
MB3788 7 ■ ABSOLUTE MAXIMUM RA TINGS * : V alue obtained when mounted on 4 cm × 4 cm doub le-sided epo xy substrate W ARNING: Semiconductor de vices can be per manently damaged by application of stress (v oltage, current, temperature , etc.) in e xcess of absolute maximum ratings.
MB3788 8 ■ ■ ■ ■ ELECTICAL CHARA CTERISTICS (Continued) (V CC =6V, T A = +25 ° C) P arameter Symbol Conditions Va l u e Unit Min T yp Max Reference voltage Ref erence voltage V REF I OR = -1 mA 2.475 2.500 2.525 V Output v oltage temperature var i a t i o n ∆ V REF / V REF T A = -30 ° to +85 ° C- 2 ± 0.
MB3788 9 (Continued) P arameter Symbol Conditions Va l u e s Unit Min T yp 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+ —— 1 2 0 — µ A Input source current I IM- —— - 2 — m A Input bias current I IB V I = 0 V -1.
MB3788 10 ■ ST AND ARD CHARA CTERISTIC CUR VES (Continued) 2.5 2.0 1.5 1.0 0.5 0 04 8 1 2 1 6 2 0 Po w e r current l CC (mA) Supply vo ltage V CC (V) 5 4 3 2 1 0 0 4 8 12 16 20 Ref erence voltage V REF ( V) Supply voltage V CC (V) CTL1, 2 = 6 V 5 4 3 2 1 0 012345 Ref e rence vol t a g e V REF (V) Supply vo ltage V CC (V) V E V REF 2.
MB3788 11 (Continued) V CC = 6 V V FB = 1.6 V T A = +25 ° C 100 80 60 40 20 0 0 5K 10K 50K 100K 500K 1M 1.9V 1.3V Duty Dtr (%) Input oscillating frequency (Hz) 40 20 0 -20 -40 1K 10K 100K 1M 5M 10M T.
MB3788 12 ■ ■ ■ ■ HO W T O SET OUTPUT V OL T A GE + - 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).
MB3788 13 ■ ■ ■ ■ HO W T O SET OUTPUT CURRENT The output circuit is configured in a push-pull type as shown in Figure 1. The ON current v alue of the output current wa vef orm shown in Figure 2 is a constant current and the OFF v alue set by RE is set b y a time constant.
MB3788 14 ■ ■ ■ ■ HO W T O SET TIME CONST ANT FOR TIMER & LA TCH-TYPE SHOR T - CIRCUIT PR O TECTION CIRCUIT If the load conditions of the s witching regulator are stable, the outputs of compar ators 1 and 2 do not change, so the SP comparator outputs a High le vel.
MB3788 15 ■ ■ ■ ■ PR OCESSING WITHOUT USING SCP PIN If the timer and latch-type shor t-circuit protection circuit is not used, connect the SCP pin (pin 15) to GND as close as possible . Also , connect the input pin of each channel comparator to the V CC pin (pin 11).
MB3788 16 ■ ■ ■ ■ EQUIV ALENT SERIES RESIST ANCE OF SMOO THING CAP A CIT OR AND ST ABILITY OF DC/DC CONVER TER The equiv alent ser ies resistance (ESR) of the smoothing capacity in a DC/DC conv er ter has a great eff ect on the loop phase characteristics.
MB3788 17 (Reference Data) The phase margin is halv e d by changing the smoothing capacitor from an alumin um electrolytic capacitor (Rc = 1.0 Ω ) to a semiconductor electrolytic capacitor (OS capacitor : Rc = 0.2 Ω ) with a low ESR (Figures 11 and 12).
MB3788 18 ■ ■ ■ ■ APPLICA TION CIRCUIT +15 V +24 V DC motor 1 DC motor 2 24 150 Ω 23 20 21 22 1000 pF Channel 1 (dB) <Logic power supply> (b) 22 µ H 3 V 10 µ F Ca2 Cb2 OUT2 VE2 150 .
MB3788 19 ■ ■ ■ ■ NO TES ON USE • T ake account of common impedance when designing the ear th line on a printed wir ing board. • T ake measures against static electricity .
MB3788 20 ■ ■ ■ ■ P A CKA GE DIMENSION 24-pin plastic SSOP (FPT-24P-M03) Note 1 ) *1 : Resin protrusion. ( Each side : + 0.15 ( .006 ) Max ) . Note 2 ) *2 : These dimensions do not include resin protrusion. Note 3 ) Pins width and pins thickness include plating thic kness.
MB3788 FUJITSU LIMITED 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.
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