Fujitsu MB3788 Manuale utente

DS04-27209-3E

FUJITSU SEMICONDUCTOR

DATA SHEET

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.

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.

Itcanbeusedinhigh-performanceportableequipmentsuchasavideocamcorderornotebookpersonalcomputer

(word processor).

■

■■

■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)

■

■■

■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)

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: 2.50 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

■

■■

■PIN ASSIGNMENT

(TOP VIEW)

VCC(out)

OUT1

VE1

Cb1

Ca1

FB1

-IN1(E)

+IN1(E)

-IN1(C)

-IN(PWN)

VCC

VREF

GND

OUT2

VE2

Cb2

Ca2

FB2

-IN2(E)

+IN2(E)

-IN2(C)

SCP

CTL2

CTL1

(FPT-24P-M03)

MB3788

■

■■

■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

3VE1I

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

1VCC2—Output circuit power pin

10 -IN(PWM) I Master oscillating waveform input

11 VCC1 —Reference power and control circuit power

12 VREF OReference voltage output

24 GND — Ground

MB3788

■

■■

■BLOCK DIAGRAM

Channel 1

-IN1 (E)

FB1

-IN1 (C)

+IN1 (E) 1

Ca1

VCC(out)

OUT1

Cb1

CTL2

VCC

CTL1

VE1

10 12 GND

-IN(PWM)

SCP

VREF

1.9 V

1.3 V

1.5 V

0.6 V

Error amplifier 1

Comparator 1

PWM comparator 1 OFF current setting

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 µA

VREF

MB3788

■

■■

■FUNCTIONAL DESCRIPTION

1. Major Functions

(1) Reference voltage power circuit

Thereference voltagepowersupply produces a referencevoltage(≈2.50V)whichistemperature-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).

(2) Error amplifier

The error amplifier detects the switching regulator output voltage and outputs a PWM control signal. It has a

wide in-phase input voltage range of -0.2 V to VCC - 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 setting 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 amplifier.

(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 mA. (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 µA 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

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.

The latch circuit turns off the output transistor and simultaneously clears the duty cycle to 0 when the output

voltage level of the comparator does not return to the normal voltage level until the capacitor voltage rises to the

base-emitterjunctionvoltage VBE (≈0.65 V) of the transistor. (See

Howto Set Time Constant forTimer & 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 voltage 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.

MB3788

■ABSOLUTE MAXIMUM RATINGS

*: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, etc.) in excess of absolute maximum ratings. Do not exceed these ratings.

■RECOMMENDED OPERATING CONDITIONS

WARNING: The recommended operating conditions are required in order to ensure the normal operation of the

semiconductor device. All of the device’s electrical characteristics are warranted when the device is

operated within these ranges.

Always use semiconductor devices within their recommended operating condition ranges. Operation

outside these ranges may adversely affect reliability and could result in device failure.

No warranty is made with respect to uses, operating conditions, or combinations not represented on

the data sheet. Users considering application outside the listed conditions are advised to contact their

FUJITSU representatives beforehand.

(TA = +25°C)

Parameter Symbol Conditions Ratings Unit

Min Max

Supply voltage VCC ——

20 V

Control input voltage VICTL ——

20 V

Allowable loss PDTa ≤+25°C—500* mW

Operating ambient temperature TOP —-30 +85 °C

Storage temperature Tstg —-55 +125 °C

(TA= +25°C)

Parameter Symbol Conditions Values Unit

Min Typ Max

Supply voltage VCC —3.66.018V

Reference voltage output current IOR —-1—0mA

Error amplifier input voltage VI—-0.2—V

CC - 1.8 V

Error amplifier input voltage VI—-0.2—V

CC V

Control input voltage VICTL —-0.2—18V

Output current IO—3.0—30mA

Operating frequency fosc — 100 300 1000 kHz

Operating ambient temperature Top — -30 25 85 °C

MB3788

■

■■

■ELECTICAL CHARACTERISTICS

(Continued)

(VCC =6V, TA= +25°C)

Parameter Symbol Conditions Value Unit

Min Typ Max

Reference

voltage

Reference voltage VREF IOR = -1 mA 2.475 2.500 2.525 V

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 = -0.1 mA to 1 mA — 3 10 mV

Short-circuit output current IOS VREF = 2 V -20 -8 -3 mA

Low voltage

malfunction

fail-safe

circuit

Threshold voltage VtH ——2.65—V

VtL ——2.45—V

Hysteresis width VHYS —80200—mV

Reset voltage VR—1.51.9—V

Short-circuit

detection

comparator

Input offset voltage VIO — 0.58 0.65 0.72 V

Input bias current IIB VI= 0 V -200 -100 — nA

In-phase input voltage range VICM —-0.2—V

CC-1.8 V

Short-circuit

detector

Threshold voltage VtPC — 0.60 0.65 0.70 V

Input standby voltage VSTB — — 50 100 mV

Input latch voltage VI— — 50 100 mV

Input source current IIbpc — -1.4 -1.0 -0.6 µA

Error

amplifier

Input offset voltage VIO VFB = 1.6 V -10 — 10 mV

Input offset current IIO VFB = 1.6 V -100 — 100 nA

Input bias current IIB VFB = 1.6 V -200 -60 — nA

In-phase input voltage range VICM —-0.2—V

CC-1.8 V

Voltage gain AV—60100—dB

Frequency bandwidth BW AV= 0 dB — 800 — kHz

In-phase signal rejection ratio CMRR — 60 80 — dB

Maximum output voltage width VOM+ —V

REF-0.3 2.4 — V

VOM- — — 0.05 0.5 V

Output sink current IOM+ VFB = 1.6 V — 120 — µA

Output source current IOM- VFB = 1.6 V — -2 — mA

MB3788

(Continued)

Parameter Symbol Conditions Values Unit

Min Typ Max

PWM

comparator

Threshold voltage Vt0 Duty cycle = 0 % 1.05 1.3 — V

Vt100 Duty cycle = 100 % — 1.9 2.25 V

Input sink current IIM+ ——120—µA

Input source current IIM- ——-2—mA

Input bias current IIB VI = 0 V -1.0 -0.5 — µA

Control

Threshold voltage Vth — 0.7 1.4 2.1 V

Input current IIH VCTL = 5 V — 100 200 µA

IIL VCTL = 0 V -10 — 10 µA

Output

Source current IO——-40—mA

Sink current IORB= 50 Ω18 30 42 mA

Output leak current ILO VO= 18 V — — 20 µA

All devices Standby current ICCO ——010µA

Power current at output OFF ICC ——1.92.7mA

MB3788

■STANDARD CHARACTERISTIC CURVES

(Continued)

2.5

2.0

1.5

1.0

0.5

0048121620

Power

current

lCC (mA)

Supply voltage VCC (V)

00 4 8 12 16 20

Reference

voltage

VREF (V)

Supply voltage VCC (V)

CTL1, 2 = 6 V

012345

Reference

voltage

VREF (V)

Supply voltage VCC (V)

VREF

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

VREF (V)

Ambient temperature TA (°C)

Output

current

setting

pin voltage

VE(V)

VCC = 6 V

VCTL1, 2 = 6 V

IOR = -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

VREF (V)

Control voltage VCTL1 (V)

500

400

300

200

100

0048121620

Control

current

lCTL1 (µA)

Control voltage VCTL1 (V)

5. Reference voltage - control voltage characteristic 6. Control current - control voltage characteristic

TA= +25°C

VCC = 6 V

TA= +25°CVCC = 6 V

TA= +25°C

CTL1 = 6 V

TA= +25°C

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