MB3785A_03_技术文档

FUJITSU SEMICONDUCTOR

DATA SHEET

DS04-27208-4E

ASSP

BIPOLAR

Switching Regulator Controller

(4 Channels plus High-Precision, High-Frequency Capabilities)

MB3785A

■ DESCRIPTION

The MB3785A is a PWM-based 4-channel switching regulator controller featuring high-precision, high-frequency

capabilities. All of the four channels of circuits allow their outputs to be set in three modes: step-down, step-up,

and inverted. The third and fourth channels are suited for DC motor speed control.

The triangular-wave oscillation circuit accepts a ceramic resonator, in addition to the standard method of oscillation

using an RC network.

■ FEATURES

• Wide range of operating power supply voltages: 4.5 V to 18 V

• Low current consumption: 6 mA [Typ] when operating10 µA or less during standby

• Built-in high-precision reference voltage generator: 2.50 V±1%

• Oscillation circuit

- Capable of high-frequency oscillation: 100 kHz to 1 MHz

- Also accepts a ceramic resonator.

• Wide input range of error amplifier: –0.2 V to V^CC–1.8 V

• Built-in timer/latch-actuated short-circuiting detection circuit

• Output circuit

- The drive output for PNP transistors is the totem-pole type allowing the on-current and off-current values to

be set independently.

(Continued)

■ PACKAGE

48-pin, Plastic LQFP

(FPT-48P-M05)

MB3785A

(Continued)

• Adjustable dead time over the entire duty ratio range

• Built-in standby and output control functions

• High-density mounting possible: 48-pin LQFP package

■ PIN ASSIGNMENT

(TOP VIEW)

Cb1

OUT1

OUT2

GND

OUT3

OUT4

VE4

VE1

VCC2

VE2

VE3

Cb4

48 47 46 45 44 43 42 41 40 39 38 37

36

Ca1

Cb2

1

2

Ca4

35

34

33

32

31

30

29

28

27

26

25

Cb3

Ca2

3

Ca3

DTC1

4

DTC4

FB4

FB1

5

−IN1 (E)

+IN1 (E)

−IN1 (C)

DTC2

6

−IN4 (E)

+IN4 (E)

−IN4 (C)

DTC3

FB3

7

8

9

FB2

10

11

12

−IN2 (E)

+IN2 (E)

−IN3 (E)

+IN3 (E)

13 14 15 16 17 18 19 20 21 22 23 24

−IN2(C) OSCOUT

OSCIN RT

CT

VREF

CTL2

CTL1 CTL3

SCP

−IN3 (C)

VCC1

(FPT-48P-M05)

Note : The alphabetic characters in parenthesis indicate the following input pins.

(C) : comparator

(E) : error amp

2

MB3785A

■ PIN DESCRIPTION

Pin No.

Symbol

I/O

Description

1

Ca1

—

CH1 output transistor OFF-current setting terminal. Insert a capacitor be-

tween the Ca1 and the Cb1 terminals, then set the output transistor OFF-cur-

rent.

48

Cb1

—

7

6

+IN1(E)

–IN1(E)

FB1

I

CH1 error amp non-inverted input terminal.

CH1 error amp inverted input terminal.

CH1 error amp output terminal.

CH1

5

O

I

8

–IN1(C)

DTC1

VE1

CH1 comparator inverted input terminal.

CH1 dead time control terminal.

4

I

47

46

3

I

CH1 output current setting terminal.

CH1 totem-pole output terminal.

OUT1

Ca2

O

—

CH2 output transistor OFF-current setting terminal. Insert a capacitor be-

tween the Ca2 and the Cb2 terminals, then set the output transistor OFF-cur-

rent.

2

Cb2

—

12

11

10

13

9

+IN2(E)

–IN2(E)

FB2

I

CH2 error amp non-inverted input terminal.

CH2 error amp inverted input terminal.

CH2 error amp output terminal.

CH2

O

I

–IN2(C)

DTC2

VE2

CH2 comparator inverted input terminal.

CH2 dead time control terminal.

I

43

44

34

I

CH2 output current setting terminal.

CH2 totem-pole output terminal.

OUT2

Ca3

O

—

CH3 output transistor OFF-current setting terminal. Insert a capacitor be-

tween the Ca3 and the Cb3 terminals, then set the output transistor OFF-cur-

rent.

35

Cb3

—

25

26

27

24

28

41

40

36

+IN3(E)

–IN3(E)

FB3

I

CH3 error amp non-inverted input terminal.

CH3 error amp inverted input terminal.

CH3 error amp output terminal.

CH3

O

I

–IN3(C)

DTC3

VE3

CH3 comparator inverted input terminal.

CH3 dead time control terminal.

I

CH3 output current setting terminal.

CH3 totem-pole output terminal.

OUT3

Ca4

O

—

CH4 output transistor OFF-current setting terminal. Insert a capacitor be-

tween the Ca4 and the Cb4 terminals, then set the output transistor OFF-cur-

rent.

37

Cb4

—

30

31

32

29

+IN4(E)

–IN4(E)

FB4

I

CH4 error amp non-inverted input terminal.

CH4 error inverted input terminal.

CH4

O

I

CH4 error amp output terminal.

–IN4(C)

CH4 comparator inverted input terminal.

(Continued)

3

MB3785A

(Continued)

Pin No.

33

Symbol

I/O

I

Description

CH4 dead time control terminal.

DTC4

VE4

CH4

38

39

I

CH4 output current setting terminal.

CH4 totem-pole output terminal.

OUT4

O

—

14

15

16

OSC^IN

OSC^OUT

RT

This terminal connects a ceramic resonator.

—

This terminal connects to a resistor for setting the triangular-wave frequency.

This terminal connects to a capacitor for setting the triangular-wave frequen-

cy.

—

17

C^T

18

45

42

19

23

V^CC1

V^CC2

GND

V^REF

—

O

Power supply terminal for the reference power supply control circuit.

Power supply terminal for the output circuit.

GND terminal.

Reference voltage output terminal.

SCP

—

This terminal connects to a capacitor for the short-circuit protection circuit.

Power supply circuit and CH1 control terminal.

When this pin is High, the power supply circuit and first channel are in

20

21

22

CTL1

CTL2

CTL3

I

active state.

When this pin is Low, the power supply circuit and first channel are in

standby state.

CH2 control terminal.

While the CTL1 terminal is High

When this pin is High, the second channel is in active state.

When this pin is Low, the second channel is in the inactive state.

CH3 and CH4 control terminal.

While the CTL1 terminal is High

When this pin is High, the third and fourth channels are in active state.

When this pin is Low, the third and fourth channels are in the inactive

state.

4

MB3785A

■ BLOCK DIAGRAM

Ca1

1

CH 1

Cb1

48

Error Amp 1

PWM comparator 1

VCC2

45

+

+IN1 (E)

7

OFF Current

Setting

−

+

−

+

−IN1 (E)

6

5

FB1

46

OUT1

−

V

REF

V

REF

Comparator 1

+

DTC

2 V

Comparator 1

8

4

−

−IN1 (C)

47

2.5 V

VE1

DTC1

3

2

CH 2

Ca2

Cb2

Error Amp 2

PWM comparator 2

OFF Current

Setting

+

+IN2 (E) 12

−

+

−

+

−IN2 (E) ¹¹

FB2 ¹⁰

⁴⁴OUT2

−

VREF

Comparator 2

V

REF

+

2 V

DTC

13

−IN2 (C)

−

Comparator 2

43

2.5 V

VE2

9

DTC2

34

CH 3

Ca3

Error Amp 3

33

PWM comparator 3

Cb3

+

25

+IN3 (E)

OFF Current

Setting

+

−

−IN3 (E)

26

27

FB3

40

OUT3

Comparator 3

100 Ω

+

0.6 V

CH 4

24

−

−IN3 (C)

41

2.5 V

VE3

Ca4

36

DTC3 ²⁸

Error Amp 4

37

PWM comparator 4

Cb4

+

+IN4 (E) 30

OFF Current

Setting

+

−

−IN4 (E)

31

FB4 ³²

39

OUT4

Comparator 4

100 Ω

+

0.6 V

29

−

−IN4 (C)

38

2.5 V

33

DTC4

VE4

SCP

Comparator

−

21

CTL2

−

+

22

CTL3

2.1 V

−

+

−1.9 V

−1.3 V

DTC

Comparator 3

1 µA

1.2 V

SCP

18

V^CC1

23

V

REF

Under Voltage

Lock-out

Protection Circuit

Ref.

Power Supply

S

R

Triangular-Wave

Oscillator Circuit

20

CTL1

Vol. Circuit & Channel

Circuit

SR Latch

Control

42

2.5 V

14

15

16

17

19

OSC^IN

RT

CT

V

REF

GND

OSCOUT

Ceramic Resonator

5

MB3785A

■ FUNCTIONAL DESCRIPTION

1. Switching Regulator Function

(1) Reference voltage circuit

The reference voltage circuit generates a temperature-compensated reference voltage ( =: 2.50 V) using the

voltage supplied from the power supply terminal (pin 18). This voltage is used as the operating power supply for

the internal circuits of the IC. The reference voltage can also be supplied to an external device from the V^REF

terminal (pin 19).

(2) Triangular-wave oscillator circuit

By connecting a timing capacitor and a resistor to the CT (pin 17) and the RT (pin 16) terminals, it is possible to

generate any desired triangular oscillation waveform. The oscillation can also be obtained by using a ceramic

resonator connected to pins 14 and 15.

This waveform has an amplitude of 1.3 V to 1.9 V and is input to the internal PWM comparator of the IC. At the

same time, it can also be supplied to an external device from the C^Tterminal (pin 17).

(3) Error amplifier

This amplifier detects the output voltage of the switching regulator and outputs a PWM control signal accordingly.

It has a wide common-mode input voltage range from –0.2 V to V^CC–1.8 V and allows easy setting from an

external power supply, making the system suitable for DC motor speed control.

By connecting a feedback resistor and capacitor from the error amplifier output pin to the inverted input pin, you

can form any desired loop gain, for stable phase compensation.

(4) PWM comparator

• CH1 & CH2

The PWM comparators in these channels are a voltage comparator with two inverted input and one non-inverted

input, that is, a voltage-pulse width converter to control the output pulse on-time according to the input voltage.

It turns on the output transistor when the triangular wave from the oscillator is higher than both the error amplifier

output and the DTC-pin voltages.

• CH3 & CH4

The PWM comparators in these channels are a voltage comparator with one inverted input and two non-inverted

inputs, that is, a voltage-pulse width converter to control the output pulse on-time according to the input voltage.

It turns on the output transistor when the triangular wave from the oscillator is lower than both the error amplifier

output and the DTC-pin voltages.

These four channels can be provided with a soft start function by using the DTC pin.

(5) Output circuit

The output circuit is comprised of a totem-pole configuration and can drive a PNP transistor (30 mA Max)

6

MB3785A

2. Channel Control Function

The MB3785A allows the four channels of power supply circuits to be controlled independently. Set the voltage

levels on the CTL1 (pin 20), CTL2 (pin 21), and CTL3 (pin 22) terminals to turn the circuit of each channel “ON”

or “OFF”, as listed below.

Table 1 Channel by Channel On/Off Setting Conditions.

CTL pin voltage level

On/Off state of channel

Power supply

circuit

CTL1

CTL2

CTL3

CH1

CH2

CH3 and CH4

H

L

ON

OFF

ON

H

ON

H

L

ON

H

L

OFF

X

Standby state*

*: The power supply current value during standby is 10 µA or less.

3. Protective Functions

(1) Timer/latch-actuated short-circuiting protection circuit

The SCP comparator checks the output voltage of each comparator which is used to detect the short-circuiting

of output. When any of these comparators have an output voltage greater than or equal to 2.1 V, the timer circuit

is activated and a protection enable capacitor externally fitted to the SCP terminal (pin 23) begins to charge.

If the comparator’s output voltage is not restored to normal voltage level by the time the capacitor voltage has

risen to the base-emitter junction voltage of the transistor, i.e., V^BE(=: 0.65 V), the latch circuit is activated to turn

off the output transistor while at the same time setting the duty (OFF) = 100 %.

When actuated, this protection circuit can be reset by turning on the power supply again.

(2) Under voltage lockout protection circuit

A transient state at power-on or a momentary drop of the power supply voltage causes the control IC to mal-

function, resulting in system breakdown or deterioration. By detecting the internal reference voltage with respect

to the power supply voltage, this protection circuit resets the latch circuit to turn off the output transistor and set

the duty (OFF) = 100 %, while at the same time holding the SCP terminal (pin 23) at the “L”. The reset is cleared

when the power supply voltage becomes greater than or equal to the threshold voltage level of this protection

circuit.

7

MB3785A

■ ABSOLUTE MAXIMUM RAGINGS (See WARNING)

(Ta = +25°C)

Rating

Parameter

Symbol

Conditions

Unit

Min

—

Max

20

Power supply voltage

Control input voltage

Power dissipation

V^CC

V^ICTL

PD

—

V

—

20

Ta ≤ +25°C

—

550*

85

mW

°C

Operating ambient temperature

Storage temperature

T^OP

—

–30

–55

Tstg

125

*: The packages are mounted on the epoxy board (4 cm × 4 cm).

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

(Ta = +25°C)

Value

Typ

6.0

—

Parameter

Symbol

Conditions

Unit

Min

4.5

Max

18

Power supply voltage*

Error amp. input voltage

Comparator input voltage

Control input voltage

Output current

V^CC

VI

—

V

–0.2

3.0

VCC –0.8

VCC

V^I

—

V

VICTL

I^O

—

18

V

—

30

mA

pF

kΩ

kHz

Timing capacitance

Timing resistance

CT

68

—

1500

100

RT

5.1

—

Oscillation frequency

f^OSC

100

500

1000

Operating ambient tem-

perature

TOP

—

–30

25

85

°C

*: The minimum value of the recommended supply voltage is 3.6 V except when the device operates with constant

output sink current.

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.

8

MB3785A

■ ELECTRICAL CHARACTERISTICS

(VCC = +6 V, Ta = +25°C)

Value

Unit

Parameter

Symbol

Conditions

IOR = –1 mA

Ta = –30°C to +85°C

Min

Typ

Max

Reference voltage

V^REF

2.475 2.500 2.525

V

Rate of changed in output

voltage vs. Temperature

∆V^REF

/VREF

–2

±0.2

2

%

Input stability

Line VCC = 3.6 V to 18 V

–10

–25

—

–2

–3

10

–3

—

mV

mA

V

Load stability

Load I^OR= –0.1 mA to –1 mA

Sort-circuit output current

I^OS

V^tH

VREF = 2 V

–8

—

2.72

2.60

120

Threshold voltage

Hysteresis width

V^tL

—

V

VHYS

80

mV

Reset voltage (V^CC)

VR

—

1.5

1.9

—

V

Input threshold voltage

Input bias current

V^th

2.45

2.50

2.55

—

V

IIB

VI = 0 V

–200

–100

nA

Input voltage range

VI

—

–0.2

—

VCC

V

Input offset voltage

Input bias current

V^IO

I^IB

0.58

0.65

0.72

—

V

–200

–100

nA

Common mode input voltage

range

V^ICM

—

–0.2

—

VCC–0.8

V

Threshold voltage

Input standby voltage

Input latch voltage

V^tPC

VSTB

VI

—

0.60

—

0.65

50

0.70

100

V

mV

—

50

Input source current

I^lbpc

—

–1.4

–1.0

–0.6

µA

Oscillation frequency

f^OSC

CT = 300 pF, RT = 6.2 kΩ 450

500

±1

550

—

kHz

%

Frequency stability (VCC)

∆f/fdv VCC = 3.6 V to 18 V

—

Frequency stability (Ta)

∆f/f^dTTa = –30°C to +85°C

–4

—

4

%

(Continued)

9

MB3785A

(Continued)

(VCC = +6 V, Ta = +25°C)

Value

Unit

Parameter

Symbol

Conditions

VFB = 1.6 V

Min

–10

Typ

Max

Input offset voltage

Input bias current

V^IO

—

10

mV

nA

IIB

VFB = 1.6 V

–200

–100

—

Common mode input voltage

range

V^ICM

—

–0.2

—

VCC–0.8

V

Voltage gain

A^V

BW

V^t0

60

—

100

800

1.9

—

dB

kHz

V

Frequency bandwidth

AV = 0 dB

Duty cycle = 0 %

Duty cycle = 100 %

Vdt = 2.3 V

—

2.25

—

Input threshold voltage

V^t100

IIbdt

IIdt

1.05

—

1.3

V

Input bias current

0.1

0.5

–80

—

µA

V

Latch mode source current

Latch input voltage

Vdt = 1.5 V

—

–500

2.4

Idt = –40 µA

Duty cycle = 0 %

Duty cycle = 100 %

Vdt = 2.3 V

VREF–0.3

1.05

—

V^Idt

V^t0

1.3

—

V

Input threshold voltage

V^t100

IIbdt

IIdt

1.9

2.25

0.5

—

V

Input bias current

—

0.1

µA

V

Latch mode source current

Latch input voltage

Threshold voltage

Vdt = 1.5 V

80

500

0.2

V^Idt

V^th

Idt = +40 µA

—

0.3

2.1

200

0.7

—

1.4

V

I^IH

VCTL = 5 V

100

µA

Input current

I^IL

VCTL = 0 V

–10

—

10

µA

Source current

Sink current

I^O

—

–40

30

—

mA

RE = 82 Ω

18

42

Output leakage current

Standby current

ILO

VO = 18 V

—

0

20

10

µA

I^CC0

Supply current when output

off

I^CC

—

6

8.6

mA

10

MB3785A

■ TYPICAL CHARACTERISTIC CURVES

1. Supply current vs. Supply voltage

2. Reference voltage vs. Supply voltage

Ta = +25°C

Ta=+25°C

10

8

5

4

3

2

1

0

CTL1 = 6 V

6

CTL1, 2

=

6 V, CTL1, 2, 3

=

6 V

4

2

0

4

8

12

16

20

0

4

8

12

Supply voltage V^CC(V)

4. Reference voltage vs. Ambient temperature

16

20

Supply voltage VCC (V)

3. Reference voltage and Output current setting

pin voltage vs. Supply voltage

2.56

2.54

2.52

2.50

2.48

2.46

2.44

5

4

3

2

1

V

CC = 6 V

Ta = +25°C

V

CTL1, 2, 3 = 6 V

I

OR = −1 mA

4

V

REF

3

2

1

0

VE

0

1

2

3

4

5

−60 −40 −20

0

20

40

60

80

100

Supply voltage VCC (V)

Ambient temperature Ta (°C)

5. Reference voltage vs. Control voltage

6. Control current vs. Control voltage

V

CC = 6V

3.0

2.8

2.6

2.4

2.2

2.0

500

400

300

200

100

0

V

CC = 6 V

Ta = +25°C

0

1

2

3

4

5

0

4

8

12

16

20

Control voltage VCTL1 (V)

(Continued)

11

MB3785A

(Continued)

8. Triangular wave frequency

vs. Timing resistance

7. Triangular wave maximum amplitude voltage

vs. Timing capacitance

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

5 M

V

CC = 6 V

V

R

CC = 6 V

= 10 kΩ

Ta= +25°

Ta = +25°

C

T

C

1 M

500 k

100 k

50 k

CT = 68 pF

C

T

= 150 pF

= 300 pF

10 k

5 k

C

50 10²5 × 10²10³5 × 10³10⁴5 × 10⁴10⁵

Timing capacitance C (pF)

CT = 1500 pF

T

CT= 15000 pF

1 k

5 k 10k

50 k 100 k

500 k 1 M

Timing resistance R

T

(Ω)

9. Triangular wave cycle vs. Timing capacitance

100

50

V

R

CC = 6 V

= 10 kΩ

Ta = +25°C

10. Duty vs. Triangular wave frequency

T

100

80

60

40

20

0

V

CC = 6 V

DT = 1.6 V

CH 1

10

5

Ta = +25°C

1

0.5

0.2

10

5 k

10k

50 k 100 k

500 k 1 M

10²

5 × 10²10³

5 × 10³10⁴

(pF)

5 × 10⁴

Triangular wave frequency (Hz)

Timing capacitance C

T

12. Rate of change in triangular wave frequency vs.

Ambient temperature

11. Rate of change in triangular wave frequency vs.

Ambient temperature

(Using ceramic resonator)

(Not using ceramic resonator)

10

5

10

5

V

CC

=

6 V

V

f

CC = 6 V

OSC = 460 kHz

(R = 6.8 kΩ, C = 280 pF)

f

OSC

450 kHz

8.5 kΩ, CT = 250 pF)

(R

T

=

T

0

−5

−10

−5

−10

−40 −20

0

20

40

60

80

100

−40 −20

0

20

40

60

80

100

Ambient temperature Ta (°C)

(Continued)

12

MB3785A

(Continued)

13. Gain vs. Frequency and Phase vs. Frequency

14. Error amp maximum output voltage vs. Frequency

3.0

Ta = +25°C

180

90

40

20

VCC = 6V

CH 1

Ta = +25°C

A^V

2.0

1.0

0

φ

−90

−−80

−20

−40

100

500 1 k

5 k 10 k

50 k 100 k

500 k 1 M

1 k

10 k

100 k

Frequency f (Hz)

1 M

10 M

Triangular wave frequency fOSC (Hz)

[Measuring Circuit]

2.5 V 2.5 V

240 kΩ

4.7 kΩ

–

+

OUT

10 µF

+

–

IN

Error amp

4.7 kΩ

15. Power dissipation vs. Ambient temperature

1000

800

600

550

LQFP

400

200

0

–30 –20

0

20

40

60

80

100

Ambient temperature Ta (°C)

13

MB3785A

■ METHODS OF SETTING THE OUTPUT VOLTAGE

1. Method of Connecting CH1 and CH2: When Output Voltage (V^O) is Positive

VREF

+

VOUT

V^REF

+

R

R1

V^O

=

–

(R1 + R2)

2 × R2

+

–

R2

RNF

2. Method of Connecting CH1 and CH2: When Output Voltage (V^O) is Negative

V^REF

2 × R1

–

VO = –

(R1 + R2) + VREF

R

R1

+

–

R2

RNF

–

VOUT

14

MB3785A

3. Method of Connecting CH3 and CH4: When Output Voltage (V^O) is Positive

VREF

VOUT

V^REF

+

R

R1

VO

=

(R1 + R2)

2 × R2

+

–

R2

RNF

4. Method of Connecting CH3 and CH4: When Output Voltage (V^O) is Negative

VREF

–

V^O= –

(R1 + R2) + VREF

2 × R1

R

R1

+

–

R2

RNF

–

VOUT

15

MB3785A

■ METHOD OF SETTING THE OUTPUT CURRENT

The output circuit is comprised of a totem-pole configuration. Its output current waveform is such that the ON-

current value is set by constant current and the OFF-current value is set by a time constant as shown in Figure

2. These output currents are set using the equations below.

• ON-current = 2.5/RE [A]

(Voltage on output current-setting pin V^E=: 2.5 V)

• OFF-current time constant=: proportional to the value of CB

Figure 1. CH1 to CH4 Output Circuit

Figure 2. Output Current Waveform

Drive transistor

CB

ON-current

OFF-current

setting block

0

OFF-current

ON-current

t

R^E

VE

Figure 3. Voltage and Current Waveforms

on Output Pin (CH1)

Figure 4. Measuring Circuit Diagram

VCC = 10 V

200 ns

5 V

V^O[ V ] 10

1000 pF

V^CC

8 pin

1

48

0

22 µH

(5 V)

45

I^O[mA ] 40

8.2

k

10 µF

I^O

VO

20

0

MB3785A

2.7

k

⁴⁶570 pF

47

−20

7 pin

82 Ω

10 mV

−40

0

0.4

0.8

1.2

t [ µs ]

1.6

2.0

16

MB3785A

■ METHOD OF SETTING TIME CONSTANT

FOR TIMER/LATCH-ACTUATED SHORT-CIRCUTING PROTECTION CIRCUIT

Figure 5 schematically shows the protection latch circuit.

The outputs from the output-shorting detection comparators 1 to 4 are respectively connected to the inverted

inputs of the SCP comparator. These inputs are always compared with the reference voltage of approximately

2.1 V which is fed to the non-inverted input of the SCP comparator.

While the switching regulator load conditions are stable, there are no changes in the outputs of the comparators

1 to 4 so that short-circuit protection control keeps equilibrium state. At this time, the voltage on the SCP terminal

(pin 23) is held at approximately 50 mV.

When load conditions change rapidly due to a short-circuiting of load, for example, the output voltage of the

comparator for the relevant channel goes “H” (2.1 V or more). Consequently, the SCP comparator outputs a “L”,

causing the transistor Q¹to turn off, and the short-circuit protection capacitor CPE (externally fitted to the SCP

terminal) begins to charge.

V^PE= 50 mV + tPE × 10^–6/CPE

0.65 = 50 mV + tPE × 10^–6/CPE

CPE = tPE/0.6 (s)

When the external capacitor C^PEis charged to approximately 0.65 V, the SR latch is set and the output drive

transistor is turned off. Simultaneously, the dead time is extended to 100% and the output voltage on the SCP

terminal (pin 23) is held “L”. As a result, the S-R latch input is closed and CPE is discharged.

Figure 5. Protection Latch Circuit

2.5 V

1 µA

23

S

R

–

+

Comparator 1

Comparator 2

Comparator 3

Comparator 4

OUT

PWM

comparator

Q2

Latch

U.V.L.O

Q¹

CPE

2.1 V

17

MB3785A

■ TREATMENT WHEN NOT USING SCP

When you do not use the timer/latch-actuated short-circuiting protection circuit, connect the SCP terminal (pin

23) to GND with the shortest distance possible. Also, connect the comparator’s input terminal for each channel

to the VCC1 terminal (pin 18).

Figure 6. Treatment When Not Using SCP

18

VCC1

–IN1 (C)

8

13 –IN2 (C)

–IN3 (C)

24

29 –IN4 (C)

23

■ OSCILLATOR FREQUENCY SETTING

The oscillator frequency can be set by connecting a timing capacitor (CT) to the CT terminal (pin 17) and a timing

resistor (RT) to the RT terminal (pin 16).

Oscillator frequency: fosc

930000

fosc (kHz)

RT(kΩ)

CT(pF)

18

MB3785A

■ METHOD OF SETTING THE TRIANGULAR-WAVE OSCILLATOR CIRCUIT

1. When Not Using Ceramic Resonator

Connect the OSCIN terminal (pin 14) to GND and leave the OSCOUT terminal (pin 15) open. This makes it possible

to set the oscillation frequency with only CT and RT.

Figure 7. When Not Using Ceramic Resonator

OSC^IN

14

OSCOUT

RT

CT

15

16

17

CT

RT

Open

2. When Using Ceramic Resonator

By connecting a ceramic resonator between OSCIN and OSCOUT as shown below, you can set the oscillation

frequency. In this case, too, CT and RT are required. Determine the values of CT and RT so that the oscillation

frequency of this RC network is about 5% to 10% lower than that of the ceramic resonator.

Figure 8. When Using Ceramic Resonator

OSC^INOSCOUT

RT

CT

14

15

16

17

Ceramic resonator

CT

RT

C1

C2

19

MB3785A

When the oscillation rise time at power switch-on is compared between a ceramic and a crystal resonator, it is

known that the crystal resonator is about 10 to 100 times slower to rise than the ceramic resonator. Therefore,

when a crystal resonator is used, system operation as a switching regulator at power switch-on becomes

unstable. To avoid this problem, it is recommended that you use a ceramic oscillator because it has a short rise

time and, hence, ensures stable operation.

• Crystal Resonator Turn-on Characteristic

2.0

1.5

1.0

0

1

2

3

4

5

t (ms)

• Ceramic Resonator Turn-on Characteristic

2.0

1.5

1.0

0

1

2

3

4

5

t (ms)

20

MB3785A

■ METHOD OF SETTING THE DEAD TIME

When the device is set for step-up inverted output based on the flyback method, the output transistor is fixed to

a full-on state (ON-duty = 100 %) at power switch-on. To prevent this problem, you may determine the voltages

on the DTC terminals (pins 4, 9, 28, and 33) from the VREF voltage so you can easily set the output transistor’s

dead time (maximum ON-duty) independently for each channel as shown below.

(1) CH1 and CH2 Channels

When the voltage on the DTC terminals (pins 4 and 9) is higher than the triangular-wave output voltage from

the oscillator, the output transistor turns off. The dead time calculation formula assuming that triangular-wave

amplitude =: 0.6 V and triangular-wave minimum voltage=: 1.3 V is given below.

Vdt – 1.3

0.6

R2

=:

Duty (OFF)

× 100 [%], V^dt=

× VREF

R1 + R2

When you do not use these DTC terminals, connect them to GND.

Figure 9. When Using DTC to Set Dead Time

Figure 10. When Not Using DTC

19

VREF

R1

R2

DTC1

(DTC2)

DTC1

(DTC2)

Vdt

(2) CH3 and CH4 Channels

When the voltage on the DTC terminals (pins 28 and 33) is lower than the triangular-wave output voltage from

the oscillator, the output transistor turns off. The dead time calculation formula assuming that triangular-wave

amplitude=: 0.6 V and triangular-wave maximum voltage=: 1.9 V is given below.

1.9 –Vdt

0.6

R2

=:

Duty (OFF)

× 100 [%], Vdt =

× VREF

R1 + R2

When you do not use these DTC terminals, connect them to V^REF.

21

MB3785A

Figure 11. When Using DTC to Set Dead

Time

Figure 12. When Not Using DTC

19

VREF

19

VREF

R1

R2

DTC3

(DTC4)

DTC3

(DTC4)

Vdt

When you use a ceramic resonator, pay attention when setting the dead time because the triangular-wave

amplitude is determined by the values of C^Tand RT.

22

MB3785A

■ METHODS OF SETTING THE SOFT START TIME

To prevent surge currents when the IC is turned on, you can set a soft start using the DTC terminal (pin 4, 9, 28

and 33).

When power is switched on, channels 1 and 2 begin discharging the capacitor (Cdt) connected the DTC1 (DTC2)

terminal, channels 3 and 4 begin charging the capacitor (Cdt) connected the DTC3 (DTC4) terminal. The soft

start process operates by comparing the soft start setting voltage, which is proportional to the DTC terminal

voltage, with the triangular waveform, and varying the ON-duty of the OUT terminal (pin 46, 44, 40 and 39).

The soft start time until the ON duty reaches 50 % is determined by the following equation:

For figure 13

Soft start time (time until output ON duty = 50%)

1.6

2.5

)

0.446 × Cdt (F) × Rdt (Ω)

ts (s) = − Cdt (F) × Rdt (Ω) × ln (

For figure 14

Soft start time (time until output ON duty = 50%)

1.6

2.5

)

1.022 × Cdt (F) × Rdt (Ω)

ts (s) = − Cdt (F) × Rdt (Ω) × ln (1 −

Figure 13. Setting Soft Start for CH1 and

CH2

Figure 14. Setting Soft Start for CH3 and

CH4

V^REF

19

VREF

Rdt

Cdt

Rdt

DTC3

(DTC4)

DTC1

(DTC2)

23

MB3785A

It is also possible to set soft start simultaneously with the dead time by configuring the DTC terminals as shown

below.

For figure 15

Soft start time (time until output ON duty = 50%)

Cdt (F) × R1 (Ω) × R2 (Ω)

R1 (Ω) + R2 (Ω)

0.36R2 (Ω)

R1 (Ω)

)

× ln (0.64 −

ts (s) = −

For figure 16

Soft start time (time until output ON duty = 50%)

Cdt (F) × R1 (Ω) × R2 (Ω)

R1 (Ω) + R2 (Ω)

1.6 (R1 (Ω) + R2 (Ω))

2.5R2 (Ω)

× ln (1 −

)

ts (s) = −

Figure 15. Setting Dead Time and Soft Start

for CH1 and CH2

Figure 16. Setting Dead Time and Soft Start

for CH3 and CH4

19

VREF

19

R1

R2

Cdt

R1

R2

DTC3

(DTC4)

DTC1

(DTC2)

Cdt

24

MB3785A

■ APPLICATION

1. Equivalent series resistor and stability of smoothing capacitor

The equivalent series resistor (ESR) of the smoothing capacitor in the DC/DC converter greatly affects the loop

phase characteristic.

The stability of the system is improved so that the phase characteristic may advance the phase to the ideal

capacitor by ESR in the high frequency region (see “Gain vs. Frequency” and “Phase vs. Frequency”).

A smoothing capacitor with a low ESR reduces system stability. Use care when using low ESR electrolytic

capacitors (OS-CON^TM) and tantalum capacitors.

Note: OS-CON is the trademark of Sanyo Electnic Co., Ltd.

DC/DC Converter Basic Circuit

L

Tr

RC

VIN

D

RL

C

Gain vs. Frequency

Phase vs. Frequency

0

20

0

(2)

(1)

−90

−20

−40

−60

(2)

(1) : RC = 0 Ω

(2) : RC = 31 mΩ

(1) : RC = 0 Ω

(2) : RC = 31 mΩ

(1)

−180

10

100

1 k

Frequency f (Hz)

10 k

100 k

10

100

1 k

Frequency f (Hz)

10 k

100 k

25

MB3785A

Reference data

If an aluminum electrolytic smoothing capacitor (RC=: 1.0 Ω) is replaced with a low ESR electrolytic capacitor

(OS-CON^TM: RC=: 0.2 Ω), the phase margin is reduced by half (see Fig. 17 and 18).

DC/DC Converter A^Vvs. φ characteristic Test Circuit

VOUT

+

VO

CNF

AV vs. φ characteristic

Between these points

−IN

+IN

−

+

VIN

FB

R2

R1

VREF/2

Error Amp.

Figure 17 DC/DC Converter +5 V output Gain vs. Phase

60

40

VCC = 10 V

RL = 25 Ω

CP = 0.1 µF

180

AV

+

VO

φ

20

90

AI Capacitor

220 µF (16 V)

RC 1.0 Ω : fOSC = 1 kHz

+

−

62 °

0

−20

−40

−90

−180

GND

10

100

1 k

10 k

100 k

Figure 18 DC/DC Converter +5 V output Gain vs. Phase

60

40

VCC = 10 V

RL = 25 Ω

CP = 0.1 µF

AV

180

90

+

VO

20

OS-CON^TM

22 µF (16 V)

RC 0.2 Ω : fOSC = 1 kHz

+

−

φ

0

27 °

−20

−40

−90

−180

GND

10

100

1 k

10 k

100 k

Frequency f (Hz)

26

MB3785A

■ EXAMPLE OF APPLICATION CIRCUIT

33 µF

V

CC

10 µH

33 µF

1000 pF

1

B

48

45

22 µH

10 µF

5 V

V

CC

A

+IN

7

8.2 kΩ

4.7 kΩ

–IN

FB

6

5

CH1

2.7 kΩ

OUT

46

47

150 kΩ

4.7 kΩ

RFB

1000 pF

10 mA

B

A

8

4

33 kΩ

DTC

250 Ω

1000 pF

3

2

24 V

27 kΩ

1 µF

C

+IN

12

4.7 kΩ

D _{15 V}

–IN

FB

11

10

CH2

OUT

150 kΩ

4.7 kΩ RFB

44

43

20 kΩ

15

µF

1000 pF

10 mA

1.8 kΩ

D

13

9

C

27 kΩ

DTC

250 Ω

1000 pF

34

35

F

Motor

Control

Signal

33 kΩ

DC motor

1 µF

22 µH

10 µF

+IN

25

8.2 kΩ

2.7 kΩ

E

–IN

FB

26

27

CH3

OUT

150 kΩ

40

41

RFB

1000 pF

10 mA

F

E

24

28

DTC

250 Ω

1000 pF

10 kΩ

H

36

37

Motor

Control

Signal

DC motor

22 µH

10 µF

+IN

30

8.2 kΩ

2.7 kΩ

G

–IN

FB

31

32

OUT

150 kΩ

39

38

CH4

RFB

1000 pF

10 mA

H

G

29

33

DTC

250 Ω

10 kΩ

V

CC

18

42

V

REF

19

23

GND

SCP

14

15

16

20

21

22

17

0.1 µF

CT

6.2 kΩ

300 pF

CTL1 CTL2 CTL3

RT

Ceramic Resonator

Output Control Signals

27

MB3785A

■ 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.

• Do not apply a negative voltage

- Applying a negative voltage of −0.3 V or less to an LSI may generate a parasitic transistor, resulting in

malfunction.

■ ORDERING INFORMATION

Part number

MB3785APFV

Package

Remarks

48-pin plastic LQFP

(FPT-48P-M05)

28

MB3785A

■ PACKAGE DIMENSION

Note 1) * : These dimensions include resin protrusion.

Note 2) Pins width and pins thickness include plating thickness.

Note 3) Pins width do not include tie bar cutting remainder.

48-pin Plastic LQFP

(FPT-48P-M05)

9.00±0.20(.354±.008)SQ

+0.40

–0.10

+.016

)SQ

–.004

*7.00

(.276

0.145±0.055

(.006±.002)

36

25

37

24

Details of "A" part

0.08(.003)

1.50 –⁺0⁰.^.1²0⁰

(Mounting height)

.059 –⁺.^.0⁰0⁰4⁸

INDEX

48

13

0.10±0.10

(.004±.004)

(Stand off)

"A"

0˚~8˚

1

12

LEAD No.

0.50(.020)

0.25(.010)

0.20±0.05

0.50±0.20

(.020±.008)

M

0.08(.003)

(.008±.002)

0.60±0.15

(.024±.006)

C

2002 FUJITSU LIMITED F48013S-c-6-10

Dimensions in mm (inches)

Note : The values in parentheses are reference values.

29

MB3785A

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, such as descriptions of function and application

circuit examples, in this document are presented solely for the

purpose of reference to show examples of operations and uses of

Fujitsu semiconductor device; Fujitsu does not warrant proper

operation of the device with respect to use based on such

information. When you develop equipment incorporating the

device based on such information, you must assume any

responsibility arising out of such use of the information. Fujitsu

assumes no liability for any damages whatsoever arising out of

the use of the information.

Any information in this document, including descriptions of

function and schematic diagrams, shall not be construed as license

of the use or exercise of any intellectual property right, such as

patent right or copyright, or any other right of Fujitsu or any third

party or does Fujitsu warrant non-infringement of any third-party’s

intellectual property right or other right by using such information.

Fujitsu assumes no liability for any infringement of the intellectual

property rights or other rights of third parties which would result

from the use of information contained herein.

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.

F0308

FUJITSU LIMITED Printed in Japan


型号：	MB3785A_03
厂家：	FUJITSU
描述：	Switching Regulator Controller (4 Channels plus High-Precision, High-Frequency Capabilities) 开关稳压器控制器（ 4通道和高精度，高频能力）稳压器开关控制器
文件：	总30页 (文件大小：277K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

MB3785A_03 [FUJITSU]

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