MB3788 - Fujitsu Limited - Datasheet.Live

DS04-27209-1E

FUJITSU SEMICONDUCTOR

DATA SHEET

ASSP

SWITCHING REGULATOR

CONTROLLER

MB3788

■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

v oltage pow er supply with a v oltage accuracy of ±1%. The maximum oper ating

frequency is 1 MHz. It is designed f or a v oltage-drop output s witching regulator

suitable for a logic power supply or speed control of a DC motor.

The MB3788 is compatible with all master ICs producing triangular wa v es, sa w-

tooth waves and sine waves with an amplitude of 1.3 to 1.9 V.

It can be used in high-perfor mance por table equipment such as a video cam-

corder or notebook personal computer (word processor).

■FEATURES

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

- Low power dissipation

- Operating: 1.9 mA (standard)

Standby: 10 µA 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 VCC - 1.8 V

- On-chip high-accuracy reference voltage circuit: 2.50 V ±1%

- Output circuit

PNP transistor driv e output pin: Push-pull type

ON/OFF current va lues 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. Ho wever ,

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)

MB3788

■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

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

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

The ref erence v oltage po wer supply produces a ref e rence v oltage (≈ 2.50 V) which is temperature-compensated b y the v oltage

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 s witching 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 powe r supply easy.

Connecting the output pin and inversion input pin of the error amplifier through a f eedback 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 v oltage of the error amplifier.

(4) Output circuit

The output circuit is configured in a push-pull f orm and uses a PNP transistor drive system to driv e 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 v oltage le v els 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 tur ned off and the shor t circuit protection capacitor

connected externally to the SCP pin (pin 15) starts charging.

The latch circuit turns off the output transistor and sim ultaneously clears the duty cycle to 0 when the output v oltage le v el o f the

comparator does not return to the normal voltage le v el until the capacitor v oltage rises to the base-emitter junction v oltage VBE

(≈ 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

le vel, resets the latch circuit, turns off the output transistor , clears the duty cycle to 0 and holds the SCP pin (pin 15) at Low le v el.

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

■RECOMMENDED OPERATING CONDITIONS

(TA = +25°C)

Parameter Symbol Conditions Ratings Unit

Supply voltage VCC —20 V

Control input voltage VICTL —20 V

Allowable loss PDTa ≤ +25°C500* mW

Operating ambient temperature TOP —-30 to +85 °C

Storage temprature Tstg —-55 to +125 °C

(TA = +25°C)

Parameter Symbol Conditions Values Unit

Min. Typical Max.

Supply voltage VCC —3.66.018V

Reference voltage output curren 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

(VCC =6V, TA = +25°C)

Parameter Symbol Conditions Value Unit

Min. Typical 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 — 0.580.650.72V

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 — 0.600.650.70V

Input standby voltage VSTB ——50100mV

Input latch voltage VI——50100mV

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

Parameter Symbol Conditions Values Unit

Min. Typical 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 curren IORB = 50 Ω18 30 42 mA

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

All devices Standby current ICCO ——010

µA

Power current at output OFF ICC ——1.92.7mA

MB3788

■STANDARD CHARACTERISTIC CURVES

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.Ref erence voltage, output current setting pin v oltage

- 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

0048 121620

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

MB3788

VCC = 6 V

VFB = 1.6 V

TA = +25°C

100

005 K10 K50 K100 K500 K1 M

1.9V

1.3V

Duty

Dtr (%)

Input oscillating frequency (Hz)

-20

-40

1 K 10 K100 K1 M5 M10 M

TA = +25°C180

-90

-180

Input waveform

Gain

(dB) Phase

φ (deg)

1000

800

600

400

200

0-20 020 406080 100

Power

dissipation

PD (mW)

Ambient temperature TA (°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 µF

240 kΩ

4.7 kΩ

VCC = 6 V

4.7 kΩ

Error amplifier

MB3788

■HOW TO SET OUTPUT VOLTAGE

VREF VOUT

RNF

VOUT = (R1 + R2)

VREF

2 × R2

Note: Set the output voltage in the positive range (VOUT > 0).

MB3788

■HOW TO 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 w a v eform 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.

OFF current

setting part

Drive Tr

OFF

current

ON current

Output

current 0

ON current

OFF current

22 µH(5 V)

3150 Ω

1000 pF

4 5 1

VCC

Iout

1000 pF

10 µF

-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

2.7 k

Vout

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-le v el signal (more than 2.1 V). Then, the SVP compar ator outputs a Lo w le vel and transistor Q1 is turned off. The short-circuit protection

capacitor CPE externally connected to the SCP pin starts to charge.

VPE = 50 mV + tPE × 10-6/CPE

0.65 = 50 mV + tPE × 10-6/CPE

CPE = tPE /0.6 (s)

Once the capacitor CPE 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 CPE.

Fig. 5 Latch-Type Short-Circuit Protection Circuit

2.1 V

Low

input

voltage

protection

circuit

SR latch-type

circuit

1 µA

CPE

OUT

2.5 V

Comparator 1

Comparator 2

PWM

comparator

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).

Fig. 6 Processing without using SCP Pin

9-IN1 (C)

VCC

16 -IN2 (C)

15 GND

SCP

MB3788

■EQUIVALENT SERIES RESISTANCE OF SMOOTHING CAPACIT OR 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 ser ies 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 semiconductor electrolytic

capacitors (such as OS capacitors) or tantalum capacitors with a low ESP. (Phase margin reduction by using an OS capacitor is explained on

the next page.)

VIN D

-20

-40

-60

101001 k10 k100 k

-90

-180

101001 k10 k100 k

(2)

(1)

(1): RC = 0 Ω

(2): RC = 31 mΩ

(2)

(1)

Gain

(dB)

Frequency f (Hz) Frequency f (Hz)

Phase

(deg)

(1): RC = 0 Ω

(2): RC = 31 mΩ

Fig. 7 Basic Voltage-Drop Type DC/DC Converter Circuit

Fig.8 Gain - Frequency Characteristic Fig.9 Phase - Frequency Charecteristic

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).

Fig. 10 DC/DC Converter AV - φ Characteristic Measurement Diagram

Fig. 11 Gain - Frequency Characteristic

Fig.12 Phase - Frequency Characteristic Curves

AV - φ characteristic between VOUT and VIN

Error amplifier

VOUT

CNF

FB VIN

VO+

-IN

+IN

VREF/2

62°

AVϕ⇒

101001 k10 k100 k

-20

-40

180

-90

-180

VCC = 10 V

RL = 25 Ω

CP = 0.1 µF

Gain

(dB)

Frequency f (Hz)

Aluminum electrolytic capacitor gain - frequency and phase - frequency characteristics (DC/DC converter +5 V output)

Aluminum electrolytic capacitor

220 µF (16 V)

Rc ≈ 1.0 Ω: fOSC = 1 kHz

VO+

Phase

(deg)

GND

ϕ⇒

101001 k10 k100 k

-20

-40

180

-90

-180

27°

VCC = 10 V

RL = 25 Ω

CP = 0.1 µF

Gain

(dB)

Frequency f (Hz)

OS capacitor gain - frequency and phase - frequency characteristics (DC/DC converter +5 V output)

OS capacitor

22 µF (16 V)

Rc ≈ 1.2 Ω: fOSC = 1 kHz

VO+

GND

Phase

(deg)

MB3788

■APPLICATION CIRCUIT

+15 V

+24 V

DC motor 1

DC motor 2

150Ω

1000 pF

Channel 1

(dB)

(b)

22 µH3 V

10 µF

Ca2

Cb2

OUT2

VE2

150 Ω

1000 pF <Logic power supply>

(a)

22 µH5 V

10 µF

Ca1

VCC(out)

OUT1

VE1

Cb1

(15 mA)

Channel 2

(deg)

10 µH

-33 µF

VCC

-IN1 (E)

FB1

-IN1 (C)

+IN1 (E)

VCC

CTL2

CTL1

(a) 4.7 kΩ

4.7 kΩ

8.2 kΩ

2.7 kΩ100 kΩ

-IN2 (E)

FB2

-IN2 (C)

+IN2 (E)

(b) 4.7 kΩ

4.7 kΩ

3.8 kΩ

2.7 kΩ100 kΩ

15 10

12 GND-IN(PWM)SCPVREF

⇑

Triangular wave signal

1.9 V

1.3 V

<MB3785A-used DC/DC converter>

0.1 µF

0.22 µF

MB3788

■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 smaller than the

minimum voltage is applied, the LSI operation will become unstable.

3. To ground the PC board, use the thic kest cab le possib le because high frequencies are used which can easily produce high-frequency 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 kΩ to 1 MΩ.

MB3788

■PACKAGE DIMENSION

24-pin plastic SSOP

(FPT-24P-M03)

Dimensions in mm (inches).

1994 FUJITSU LIMITED F24018S-2C-2

0.50±0.20

(.020±.008)

0.10±0.10(.004±.004)

(STAND OFF)

0 10°

Details of "A" part

7.75±0.10(.305±.004)

0.65±0.12(.0256±.0047)

7.15(.281)REF

6.60(.260)5.60±0.10 NOM

7.60±0.20

(.220±.004) (.299±.008)

"A"

.006 –.001

+.002

–0.02

+0.05

0.15

.049 –.004

+.008

–0.10

+0.20

1.25

.009 –.002

+.004

–0.05

+0.10

0.22

0.10(.004)

INDEX

(Mounting height)

MB3788

FUJITSU LIMITED

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.

The products described in this document are designed, developed

and manufactured as contemplated for general use, including

without limitation, ordinary industrial use, general office use,

personal use, and household use, but are not designed, developed

and manufactured as contemplated (1) for use accompanying fatal

risks or dangers that, unless extremely high safety is secured, could

have a serious effect to the public, and could lead directly to death,

personal injury, severe physical damage or other loss (i.e., nuclear

reaction control in nuclear facility, aircraft flight control, air traffic

control, mass transport control, medical life support system, missile

launch control in weapon system), or (2) for use requiring

extremely high reliability (i.e., submersible repeater and artificial

satellite).

Please note that Fujitsu will not be liable against you and/or any

third party for any claims or damages arising in connection with

above-mentioned uses of the products.

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.

F9902

 FUJITSU LIMITED Printed in Japan