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DS04-27209-3E

FUJITSU SEMICONDUCTOR

DATA SHEET

ASSP

SWITCHING REGULATOR

CONTROLLER

MB3788

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DESCRIPTION

The MB3788 is a dual-channel PWM-type switching regulator controller; it incorporates 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 V to 1.9 V.

It can be used in high-performance portable equipment such as a video camcorder or notebook personal computer

(word processor).

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FEATURES

• Wide operating power supply voltage range: 3.6 V to 18 V

• Low power dissipation

• Operating: 1.9 mA (standard)

Standby: 10 µA Max

(Continued)

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PACKAGE

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 application of any voltage higher than maximum rated voltages to this high

impedance circuit.

24-pin Plastic SSOP

(FPT-24P-M03)

Summary of content (21 pages)

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FUJITSU SEMICONDUCTOR DATA SHEET DS04-27209-3E ASSP SWITCHING REGULATOR CONTROLLER MB3788 ■ DESCRIPTION The MB3788 is a dual-channel PWM-type switching regulator controller; it incorporates 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.
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MB3788 (Continued) • 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 VCC - 1.8 V • On-chip high-accuracy reference voltage circuit: 2.
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MB3788 ■ PIN DESCRIPTION Pin No. Channel 1 Channel 2 Control circuit Power circuit Pin name I/O Descriptions 2 OUT1 O Channel 1 push-pull type output 3 VE1 I Channel 1 output current setting 4 Ca1 — 5 Cb1 — Channel 1 output transistor OFF current setting: Output transistor OFF The current is set by connecting a capacitor between pins Ca1 and Cb1.
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MB3788 ■ BLOCK DIAGRAM Cb1 Channel 1 4 5 Ca1 +IN1 (E) + 8 -IN1 (E) 7 FB1 6 OFF current setting + - Comparator 1 VCC(out) 2 OUT1 3 0.6 V - 9 1 PWM comparator 1 - + -IN1 (C) Error amplifier 1 VE1 1.5 V Ca2 Channel 2 20 21 Cb2 +IN2 (E) 17 -IN2 (E) 18 FB2 19 + OFF current setting + - PWM comparator 2 - + 0.6 V -IN2 (C) Error amplifier 2 16 Timer circuit 23 Comparator 2 OUT2 22 VE2 1.5 V - SCP comparator + 14 CTL2 11 VCC 13 CTL1 1.9 V 1.3 V 2.
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MB3788 ■ 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 VREF pin (pin12).
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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 voltage of one comparator increases to 2.1 V, the transistor of the timer circuit is turned off and the short circuit protection capacitor connected externally to the SCP pin (pin 15) starts charging.
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MB3788 ■ ABSOLUTE MAXIMUM RATINGS (TA = +25°C) Parameter Symbol Conditions Supply voltage VCC Control input voltage Ratings Unit Min Max — — 20 V VICTL — — 20 V Allowable loss PD Ta ≤ +25°C — 500* mW Operating ambient temperature TOP — -30 +85 °C Storage temperature Tstg — -55 +125 °C *: Value obtained when mounted on 4 cm × 4 cm double-sided epoxy substrate WARNING: Semiconductor devices can be permanently damaged by application of stress (voltage, current, temperature,
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MB3788 ■ ELECTICAL CHARACTERISTICS (VCC =6V, TA = +25°C) Parameter Reference voltage Low voltage malfunction fail-safe circuit Short-circuit detection comparator Short-circuit detector Error amplifier Symbol Conditions Value Unit Min Typ Max 2.475 2.500 2.525 V Reference voltage VREF IOR = -1 mA Output voltage temperature variation ∆VREF/ VREF TA = -30° to +85°C -2 ±0.2 2 % Input stability Line VCC = 3.6 V to 18 V — 2 10 mV Load stability Load IOR = -0.
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MB3788 (Continued) Parameter Symbol Conditions Vt0 Duty cycle = 0 % Vt100 Duty cycle = 100 % Values Unit Min Typ Max 1.05 1.3 — V — 1.9 2.25 V Threshold voltage PWM comparator Input sink current IIM+ — — 120 — µA Input source current IIM- — — -2 — mA Input bias current IIB -1.0 -0.5 — µA Threshold voltage Vth 0.7 1.4 2.
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MB3788 ■ STANDARD CHARACTERISTIC CURVES 1. Power current - supply voltage characteristic 2. Reference voltage - supply voltage characteristic TA = +25°C CTL1 = 6 V 2.5 TA = +25°C 5 2.0 4 CTL1, 2 = 6 V Power 1.5 current lCC (mA) 1.0 Reference 3 voltage VREF (V) 2 0.5 1 0 0 4 8 12 16 0 0 20 4 8 3.Reference voltage, output current setting pin voltage - supply voltage characteristic TA = +25°C 5 4 Reference voltage 3 VREF (V) VE 2 3 4 VCC = 6 V VCTL1, 2 = 6 V IOR = -1 mA Reference 2.
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MB3788 (Continued) 8.Gain - frequency characteristic and phase - frequency characteristic 7. Duty - input oscillating frequency characteristic 100 Input waveform Duty Dtr (%) VCC = 6 V VFB = 1.6 V TA = +25°C 1.9V 1.3V 80 TA = +25°C 40 90 20 Gain (dB) 0 60 40 180 Phase 0 φ (deg) 20 -90 -20 0 0 5K 10K 50K 100K 500K 1M Input oscillating frequency (Hz) -180 -40 1K 10K 100K 1M 5M 10M f (Hz) 9.
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MB3788 ■ HOW TO SET OUTPUT VOLTAGE VREF VOUT VOUT = R R1 + - R R2 RNF Note: Set the output voltage in the positive range (VOUT > 0).
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MB3788 ■ 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/RE (A) (Output current setting pin voltage: VE ≈ 1.5 V) • The OFF current time constant is proportional to the value of CB.
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MB3788 ■ 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 comparator 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 channel becomes a High-level signal (more than 2.1 V).
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MB3788 ■ 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 possible. Also, connect the input pin of each channel comparator to the VCC pin (pin 11). 11 VCC 9 -IN1 (C) 16 -IN2 (C) SCP 15 GND 24 Fig.
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MB3788 ■ 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 characteristics. 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.
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MB3788 (Reference Data) The phase margin is halved by changing the smoothing capacitor from an aluminum 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). VOUT VO+ CNF AV - φ characteristic between VOUT and VIN + - FB R2 -IN VIN +IN R1 VREF/2 Error amplifier Fig.
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MB3788 ■ APPLICATION CIRCUIT 10 µH VCC 13 + - + - 33 µF 11 14 VCC CTL1 CTL2 4.7 kΩ 8 Cb1 +IN1 (E) Ca1 5 VCC(out) 1 OUT1 2 8.2 kΩ 7 2.7 kΩ 0.22 µF 4 1000 pF 4.7 kΩ (a) Channel 1 (dB) -IN1 (E) 100 kΩ 9 -IN1 (C) 17 +IN2 (E) VE1 5V + - 150 Ω 3 (15 mA) (b) 4.7 kΩ Ca2 20 Cb2 21 OUT2 23 1000 pF 3.8 kΩ 18 -IN2 (E) Channel 2 (deg) 100 kΩ 19 FB2 16 -IN2 (C) VREF 12 22 µH 3V + - 150 Ω VE2 SCP -IN(PWM) GND 10 24 15 0.
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MB3788 ■ NOTES ON USE • Take account of common impedance when designing the earth line on a printed wiring board. • Take measures against static electricity. - For semiconductors, use antistatic or conductive containers. - When storing or carrying a printed circuit board after chip mounting, put it in a conductive bag or container. - The work table, tools and measuring instruments must be grounded. - The worker must put on a grounding device containing 250 kΩ to 1 MΩ resistors in series.
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MB3788 ■ PACKAGE DIMENSION Note 1) Note 2) Note 3) Note 4) 24-pin plastic SSOP (FPT-24P-M03) *1 : Resin protrusion. (Each side : +0.15 (.006) Max) . *2 : These dimensions do not include resin protrusion. Pins width and pins thickness include plating thickness. Pins width do not include tie bar cutting remainder. 0.17±0.03 (.007±.001) *17.75±0.10(.305±.004) 24 13 *2 5.60±0.10 7.60±0.20 (.220±.004) (.299±.008) INDEX Details of "A" part +0.20 1.25 –0.10 +.008 .049 –.004 (Mounting height) 0.25(.
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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.