MB3785APFV_技术文档

FUJITSU SEMICONDUCTOR

DATA SHEET

DS04-27208-1E

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

(Continued)

■ PACKAGE

48-pin, Plastic LQFP

(FPT-48P-M05)

MB3785A

(Continued)

• 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.

• 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)

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

Ca1

Cb2

1

2

36

35

Ca4

Cb3

Ca2

34

3

4

Ca3

DTC1

FB1

33

32

DTC4

5

6

FB4

–IN1 (E)

+IN1 (E)

–IN1 (C)

DTC2

31

30

29

28

27

26

25

–IN4 (E)

7

8

9

+IN4 (E)

–IN4 (C)

DTC3

FB2

10

11

12

FB3

–IN2 (E)

+IN2 (E)

–IN3 (E)

+IN3 (E)

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

(FPT-48P-M05)

Each alphabet in parentheses following the pin symbol indicates the input pin of the next circuit.

(C) denotes a comparator.

(E) denotes an error amplifier.

2

MB3785A

■ PIN DESCRIPTION

Pin No.

Symbol

Ca1

I/O

—

I

Description

1

CH1 output transistor OFF-current setting pin. Insert a capacitor between

the Ca1 and the Cb1 pins, then set the output transistor OFF-current.

48

7

Cb1

+IN1(E)

–IN1(E)

FB1

CH1 error amp non-inverted input pin.

CH1 error amp inverted input pin.

CH1 error amp output pin.

6

I

CH1

5

O

I

8

–IN1(C)

DTC1

VE1

CH1 comparator inverted input pin.

CH1 dead time control pin.

4

I

47

46

3

I

CH1 output current setting pin.

CH1 totem-pole output pin.

OUT1

Ca2

O

—

I

CH2 output transistor OFF-current setting pin. Insert a capacitor between

the Ca2 and the Cb2 pins, then set the output transistor OFF-current.

2

Cb2

12

11

10

13

9

+IN2(E)

–IN2(E)

FB2

CH2 error amp non-inverted input pin.

CH2 error amp inverted input pin.

CH2 error amp output pin.

I

CH2

O

I

–IN2(C)

DTC2

VE2

CH2 comparator inverted input pin.

CH2 dead time control pin.

I

43

44

34

35

25

26

27

24

28

41

40

36

37

30

31

32

29

I

CH2 output current setting pin.

CH2 totem-pole output pin.

OUT2

Ca3

O

—

I

CH3 output transistor OFF-current setting pin. Insert a capacitor between

the Ca3 and the Cb3 pins, then set the output transistor OFF-current.

Cb3

+IN3(E)

–IN3(E)

FB3

CH3 error amp non-inverted input pin.

CH3 error amp inverted input pin.

CH3 error amp output pin.

I

CH3

O

I

–IN3(C)

DTC3

VE3

CH3 comparator inverted input pin.

CH3 dead time control pin.

I

CH3 output current setting pin.

CH3 totem-pole output pin.

OUT3

Ca4

O

—

I

CH4 output transistor OFF-current setting pin. Insert a capacitor between

the Ca4 and the Cb4 pins, then set the output transistor OFF-current.

Cb4

+IN4(E)

–IN4(E)

FB4

CH4 error amp non-inverted input pin.

CH4 error inverted input pin.

CH4

I

O

I

CH4 error amp output pin.

–IN4(C)

CH4 comparator inverted input pin.

(Continued)

3

MB3785A

(Continued)

Pin No.

33

Symbol

I/O

I

Description

DTC4

VE4

CH4 dead time control pin.

CH4 output current setting pin.

CH4 totem-pole output pin.

CH4

38

39

14

I

OUT4

OSC^IN

O

—

This pin connects a ceramic resonator.

15

16

17

OSC^OUT

R^T

—

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

This pin connects to a capacitor for setting the triangular-wave frequency.

C^T

18

45

42

19

V^CC1

V^CC2

GND

V^REF

—

O

Power supply pin for the reference power supply control circuit.

Power supply pin for the output circuit.

GND pin.

Reference voltage output pin.

23

20

SCP

—

I

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

Power supply circuit and first-channel control pin.

CTL1

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

active state.

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

standby state.

21

22

CTL2

CTL3

I

Second-channel control pin.

While the CTL1 pin 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.

Third and fourth-channel control pin.

While the CTL1 pin 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

46

47

+

–

+IN1 (E)

7

OFF Current

Setting

–

+

–

–IN1 (E)

FB1

6

5

OUT1

V

REF

VREF

Comparator 1

+

–

DTC

2 V

Comparator 1

8

4

–IN1 (C)

DTC1

2.5 V

VE1

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)

FB3

26

27

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

VREF

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^REFterminal (pin 19).

(2) Triangular-wave oscillator circuit

By connecting a timing capacitor and a resistor to the C^T(pin 17) and the R^T(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

First channel Second channel

Power supply

circuit

3rd and 4th chan-

nels

CTL1

CTL2

CTL3

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 malfunction,

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)

Parameter

Power supply voltage

Control input voltage

Power dissipation

Symbol

V^CC

Conditions

Rating

20

Unit

V

—

V^ICTL

P^D

20

V

Ta ≤ +25°C

550*

mW

Operating ambient

temperature

T^OP

T^stg

—

–30 to 85

°C

Storage temperature

–55 to 125

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

WARNING: Permanent device damage may occur if the above Absolute Maximum Ratings are exceeded.

Functional operation should be restricted to the conditions as detailed in the operational sections of

this data sheet. Exposure to absolute maximum rating conditions for extended periods may affect

device reliability.

■ RECOMMENDED OPERATING CONDITIONS

(Ta = +25°C)

Value

Parameter

Symbol

Conditions

Unit

Min.

4.5

Typ.

6.0

—

Max.

18

Power supply voltage*

Error amp. input voltage

Comparator input voltage

Control input voltage

Output current

V^CC

V^I

—

V

–0.2

3.0

V^CC–0.8

V^CC

V^I

—

V

V^ICTL

I^O

—

18

V

—

30

mA

pF

kΩ

kHz

Timing capacitance

Timing resistance

C^T

68

—

1500

100

R^T

5.1

—

Oscillation frequency

f^OSC

100

500

1000

Operating ambient

temperature

T^OP

—

–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.

8

MB3785A

■ ELECTRICAL CHARACTERISTICS

(V^CC= +6 V, Ta = +25°C)

Value

Unit

Parameter

Symbol

Conditions

I^OR= –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

/V^REF

–2

±0.2

2

%

Input stability

Line V^CC= 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

V^REF= 2 V

–8

—

2.72

2.60

120

Threshold voltage

Hysteresis width

V^tL

—

V

V^HYS

80

mV

Reset voltage (V^CC)

V^R

—

1.5

1.9

—

V

Input threshold voltage

Input bias current

V^th

I^IB

2.45

2.50

2.55

—

V

V^I= 0 V

–200

–100

nA

Input voltage range

V^I

—

–0.2

—

V^CC

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

—

V^CC–1.8

V

Threshold voltage

Input standby voltage

Input latch voltage

V^tPC

V^STB

V^I

—

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

C^T= 300 pF, R^T= 6.2 kΩ

450

—

500

±1

550

—

kHz

%

Frequency stability (V^CC)

∆f/f^dvV^CC= 3.6 V to 18 V

Frequency stability (Ta)

∆f/f^dTTa = –30°C to +85°C

–4

—

4

%

(Continued)

9

MB3785A

(Continued)

(V^CC= +6 V, Ta = +25°C)

Value

Unit

Parameter

Symbol

Conditions

Min.

–10

Typ.

Max.

Input offset voltage

Input bias current

V^IO

I^IB

V^FB= 1.6 V

—

10

mV

nA

–200

–100

—

Common mode input

voltage range

V^ICM

—

–0.2

—

V^CC–1.8

V

Voltage gain

A^V

BW

V^t0

60

—

100

800

1.9

—

dB

kHz

V

Frequency bandwidth

A^V= 0 dB

Duty cycle = 0 %

Duty cycle = 100 %

V^dt= 2.3 V

—

2.25

—

Input threshold voltage

V^t100

I^Ibdt

I^Idt

1.05

—

1.3

V

Input bias current

0.1

0.5

–80

µA

Latch mode source current

V^dt= 1.5 V

—

–500

V^REF–

0.3

Latch input voltage

V^Idt

I^dt= –40 µA

2.4

—

V

V^t0

V^t100

I^Ibdt

I^Idt

Duty cycle = 0 %

Duty cycle = 100 %

V^dt= 2.3 V

1.05

—

1.3

1.9

0.1

500

0.2

1.4

100

—

2.25

0.5

—

V

Input threshold voltage

Input bias current

—

µA

V

Latch mode source current

Latch input voltage

Threshold voltage

V^dt= 1.5 V

80

—

V^Idt

V^th

I^IH

I^dt= +40 µA

—

0.3

2.1

200

0.7

—

V

V^CTL= 5 V

µA

Input current

I^IL

V^CTL= 0 V

–10

—

10

µA

Source current

Sink current

I^O

—

–40

30

—

mA

R^E= 82 Ω

18

42

Output leakage current

Standby current

I^LO

V^O= 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

10

8

5

4

3

Ta = +25°C

CTL1 = 6 V

6

CTL1, 2 = 6 V,

CTL1, 2, 3 = 6 V

4

2

1

0

4

8

12

Supply voltage V^CC(V)

4. Reference voltage vs. Ambient temperature

16

20

0

4

8

12

16

20

Supply voltage V^CC(V)

3. Reference voltage and Output current setting

pin voltage vs. Supply voltage

2.56

2.54

2.52

V

CC = 6 V

5

4

5

Ta = +25°C

V

CTL1, 2,3 = 6 V

I

OR = –1 mA

4

VREF

3

2

1

3

2

1

2.50

2.48

2.46

2.44

V

E

0

1

2

3

4

5

–60 –40 –20

0

20

40

60

(°C)

80

100

Supply voltage VCC (V)

Ambient temperature T

a

5. Reference voltage vs. Control voltage

6. Control current vs. Control voltage

V

CC = 6 V

V

CC = 6 V

3.0

2.8

2.6

500

400

300

Ta = +25°C

2.4

2.2

200

100

0

2.0

0

1

2

3

4

5

0

4

8

12

16

20

Control voltage V^CTL1(V)

(Continued)

11

MB3785A

(Continued)

8. Triangular wave frequency

vs. Timing resistance

7. Triangular wave maximum amplitude voltage

vs. Timing capacitance

5 M

2.4

2.2

2.0

1.8

1.6

1.4

1.2

V

CC = 6 V

V

CC = 6 V

Ta = +25°C

RT = 10 k

Ta = +25°C

1 M

500 K

100 K

50 K

CT

= 68 pF

1.0

0

C

T

= 150 pF

10 K

5 K

CT = 300 pF

50 10²

5 × 10²10³

5 × 10³10⁴

(pF)

5 × 10⁴10⁵

Timing capacitance C

T

CT = 15000 pF

CT = 1500 pF

1 K

5 K10 K 50 K100 K 500 K1 M

Timing resistance R (Ω)

T

9. Triangular wave cycle vs. Timing capacitance

100

50

10. Duty vs. Triangular wave frequency

VCC = 6 V

100

80

60

40

20

0

R

T

= 10 kΩ

V

CC = 6 V

CH 1

Ta = +25°C

VDT = 1.60 V

10

5

Ta = +25°C

1

0.5

0.2

5 K 10 K

50 K 100 K

500 K 1 M

10²5 × 10²10³

5 × 10³10⁴

(pF)

5 × 10⁴

10

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

V

f

CC = 6 V

OSC = 450 kHz

(R = 8.5 kΩ, C = 250 pF)

V

f

CC = 6 V

OSC = 460 kHz

(R = 6.8 k, C = 280 pF)

T

5

0

T

0

–5

–10

–40 –20

0

20

40

60

80 100

–10

–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

Ta = +25°C

3.0

2.0

40

20

180

90

VCC = 6V

CH 1

Ta = +25°C

Aϑ

0

φ

1.0

0

–20

–40

–90

–180

100

500 1 K

5 K10 K

50 K 100 K 500 K 1 M

1 K

10 K

100 K

1 M

10 M

Triangular wave frequency fOSC (Hz)

Frequency f (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 Channels 1 and 2: When Output Voltage (V^O) is Positive

VREF

+

OUT

V

REF

+

=

–

R

1

VO

(R1

+ R )

2

2 × R

2

+

–

R2

RNF

2. Method of Connecting Channels 1 and 2: When Output Voltage (V^O) is Negative

VREF

V

REF

–

VO

= –

(R1

+ R ) + VREF

2

2 × R

1

R

1

+

–

R2

RNF

–

OUT

V

14

MB3785A

3. Method of Connecting Channels 3 and 4: When Output Voltage (V^O) is Positive

V

REF

V

OUT

V

REF

+

=

R

1

V

O

(R1

+ R )

2

2 × R

2

+

–

R

2

RNF

4. Method of Connecting Channels 3 and 4: When Output Voltage (V^O) is Negative

V

REF

V

REF

–

= –

V

O

(R1

+ R ) + VREF

2

2 × R

1

R

1

+

–

R2

RNF

–

OUT

V

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/R^E[A]

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

• OFF-current time constant = proportional to the value of C^B

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

R^E

VE

t

Figure 3. Voltage and Current Waveforms

on Output Pin (CH1)

Figure 4. Measuring Circuit Diagram

V

CC = 10 V

10

1000 pF

VCC

8 pin

22 µH

1

48

0

40

(5 V)

45

8.2

k

10 µF

IO

V

O

MB3785A

2.7

k

⁴⁶570 pF

20

0

47

7 pin

82 Ω

–20

–40

0

0.4

0.8

1.2

1.6

2.0

t (µS)

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 C^PE(externally fitted to the SCP

terminal) begins to charge.

V^PE= 50 mV + t^PE× 10^–6/C^PE

0.65 = 50 mV + t^PE× 10^–6/C^PE

C^PE= t^PE/0.6 (sec)

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 C^PEis 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

Q

2

Latch

U.V.L.O

Q

1

C

PE

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

V^CC1terminal (pin 18).

Figure 6. Treatment When Not Using SCP

18

V

CC1

–IN1 (C)

8

13 –IN2 (C)

–IN3 (C)

24

29 –IN4 (C)

23

18

MB3785A

■ METHOD OF SETTING THE TRIANGULAR-WAVE OSCILLATOR CIRCUIT

1. When Not Using Ceramic Resonator

Connect the OSC^INterminal (pin 14) to GND and leave the OSC^OUTterminal (pin 15) open. This makes it possible

to set the oscillation frequency with only C^Tand R^T.

Figure 7. When Not Using Ceramic Resonator

OSC^IN

14

OSCOUT

R

T

C

T

15

16

17

CT

RT

Open

2. When Using Ceramic Resonator

By connecting a ceramic resonator between OSC^INand OSC^OUTas shown below, you can set the oscillation

frequency. In this case, too, C^Tand R^Tare required. Determine the values of C^Tand R^Tso that the oscillation

frequency of this RC network is about 5-10% 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 (msec)

• Ceramic Resonator Turn-on Characteristic

2.0

1.5

1.0

0

1

2

3

4

5

t (msec)

20

MB3785A

■ METHOD OF SETTING THE DEAD TIME AND SOFT START

1. 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 V^REFvoltage 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.

V^dt– 1.3

0.6

R²

Duty (OFF) =

× 100 [%], V^dt=

× V^REF

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

V

REF

R1

DTC1

(DTC2)

Vdt

R2

(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 traingular-wave amplitude

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

1.9 –V^dt

0.6

R²

Duty (OFF)

× 100 [%], V^dt=

× V^REF

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

V

REF

19

V

REF

R1

DTC3

(DTC4)

DTC3

(DTC4)

Vdt

R2

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 R^T.

2. Soft Start

To prevent inrush current at power switch-on, the device can be set for soft start by using the DTC terminals (pins

4, 9, 28, and 33). The diagrams below show how to set.

Figure 13. Setting Soft Start for CH1 and

CH2

Figure 14. Setting Soft Start for CH3 and

CH4

V

REF

19

V

REF

Rdt

Cdt

Rdt

DTC3

(DTC4)

DTC1

(DTC2)

22

MB3785A

Itis also possible to set softstartsimultaneously with the dead time byconfiguringthe DTC terminals asshown below.

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

V

REF

19

R1

Cdt

R1

DTC3

(DTC4)

DTC1

(DTC2)

Cdt

R2

23

MB3785A

■ EQUIVALENT SERIES RESISTOR AND STABILITY OF SMOOTHING CAPACITOR

The equivalent series resistance (ESR) of a smoothing capacitor in a DC/DC converter greatly affects the phase

characteristics of the loop depending on its value.

System stability is improved by ESR because it causes the phase to lead that of the ideal capacitor in high-frequency

regions. (See Figures 17 and 19.) Conversely, if a low-ESR smoothing capacitor is used, system stability deterio-

rates. Therefore, use of a low-ESR semiconductor electrolytic capacitors (OS – CON) or tantalum capacitors calls

for careful attention.

Figure 17. Basic Circuit of Stepdown DC/DC Converter

L

Tr

RC

V

IN

D

RL

C

Figure 18. Gain-Frequency Characteristic

Figure 19. Phase-Frequency Characteristic

20

0

(2)

–90

–20

(2)

(1) : R

C

= 0 Ω

–40

(1)

(1) : R

C

= 0 Ω

(2) : R

= 31 mΩ

(1)

(2) : R

= 31 mΩ

–180

–60

10

100

1 k

10 k

100 k

10

100

1 k

10 k

100 k

Frequency f (Hz)

24

MB3785A

(Reference Data)

The phase margin is halved by changing the smoothing capacitor from an aluminum electrolytic capacitor (R^C=

1.0 Ω) to a small-ESR semiconductor electrolytic capacitor (OS – CON; R^C= 0.2 Ω). (See Figure 21 and 22.)

Figure 20. DC/DC Converter AV-φ Characteristic Measuring Circuit

VOUT

+

O

V

CNF

AV–ø characteristic

between this interval

–IN

+IN

+

–

VIN

FB

R2

R1

VREF/2

Error amp

Figure 21. Gain-Frequency Characteristic

Gain - frequency and phase frequency characteristics of Al electrolytic capacitor (DC/DC converter +5 V output)

60

VCC = 10 V

R

L

= 25 Ω

= 0.1 µF

40

20

180

90

AV

CP

+

O

V

ϕ

+ Al electrolytic capacitor

62°

220 µF (16 V)

0

–

RC

1.0 Ω : FOSC = 1 kHz

–20

–40

–90

GND

–180

10

100

1 k

Frequency f (Hz)

10 k

100 k

Figure 22. Phase-Frequency Characteristic

Gain - frequency and phase frequency characteristics of OS – CON (DC/DC converter +5 V output)

60

VCC = 10 V

R^L= 25 Ω

A^V

40

20

180

90

+

C^P= 0.1 µF

VO

OS – CON

22 µF (16 V)

+

–

ϕ

27°

0

R^C0.2 Ω : fOSC = 1 kHz

–20

–40

–90

GND

–180

10

100

1 k

10 k

100 k

Frequency f (Hz)

25

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

CHI

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 k

300 pF

CTL1 CTL2 CTL3

RT

Ceramic Resonator

Output Control Signals

26

MB3785A

■ PRECAUTIONS ON USING THE DEVICE

1. Do not input voltages greater than the maximum rating.

Inputting voltages greater than the maximum rating may damage the device.

2. Always use the device under recommended operating conditions.

Ifa voltage greaterthan the maximum value is inputto the device, its electrical characteristics may not be guaranteed.

Similarly, inputting a voltage below the minimum value may cause device operation to become unstable.

3. For grounding the printed circuit board, use as wide ground lines as possible to prevent

high-frequency noise.

Because the device uses high frequencies, it tends to generate high-frequency noise.

4. Take the following measures for protection against static charge:

• For containing semiconductor devices, use an antistatic or conductive container.

• When storing or transporting device-mounted circuit boards, use a conductive bag or container.

• Ground the workbenches, tools, and measuring equipment to earth.

• Make sure that operators wear wrist straps or other appropriate fittings grounded to earth via a resistance of

250 k to 1 M ohms placed in series between the human body and earth.

■ ORDERING INFORMATION

Part number

MB3785APFV

Package

Remarks

48-pin plastic LQFP

(FPT-48P-M05)

27

MB3785A

■ PACKAGE DIMENSION

48-pin Plastic LQFP

(FPT-48P-M05)

9.00±0.20(.354±.008)SQ

7.00±0.10(.276±.004)SQ

1.50 ⁺^0.⁰¹^.⁰²⁰

.059 ⁺^.0^.⁰⁰⁴⁰⁸

(MOUNTING HEIGHT)

36

25

37

24

5.50

(.217)

REF

8.00

(.315)

NOM

INDEX

Details of "A" part

48

13

1

12

LEAD No.

"A"

0.18 ⁺^0.⁰⁰^.³⁰⁸

.007 ⁺^.0^.⁰⁰¹⁰³

0.127 ⁺^0.⁰⁰^.²⁰⁵

.005 ⁺^.0^.⁰⁰¹⁰²

0.10±0.10

(.004±.004)

0.50±0.08

(.0197±.0031)

(STAND OFF)

0.50±0.20

(.020±.008)

0

10˚

0.10(.004)

C

1995 FUJITSU LIMITED F48013S-2C-5

Dimensions in: mm (inches)

28

MB3785A

FUJITSU LIMITED

For further information please contact:

Japan

FUJITSU LIMITED

Corporate Global Business Support Division

Electronic Devices

KAWASAKI PLANT, 4-1-1, Kamikodanaka

Nakahara-ku, Kawasaki-shi

Kanagawa 211-8588, Japan

Tel: (044) 754-3763

The contents of this document are subject to change without

notice. Customers are advised to consult with FUJITSU sales

representatives before ordering.

Fax: (044) 754-3329

http://www.fujitsu.co.jp/

The information and circuit diagrams in this document 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.

North and South America

FUJITSU MICROELECTRONICS, INC.

Semiconductor Division

3545 North First Street

San Jose, CA 95134-1804, USA

Tel: (408) 922-9000

Fax: (408) 922-9179

FUJITSU semiconductor devices are intended for use in

standard applications (computers, office automation and other

office equipment, industrial, communications, and measurement

equipment, personal or household devices, etc.).

CAUTION:

Customers considering the use of our products in special

applications where failure or abnormal operation may directly

affect human lives or cause physical injury or property damage,

or where extremely high levels of reliability are demanded (such

as aerospace systems, atomic energy controls, sea floor

repeaters, vehicle operating controls, medical devices for life

support, etc.) are requested to consult with FUJITSU sales

representatives before such use. The company will not be

responsible for damages arising from such use without prior

approval.

Customer Response Center

Mon. - Fri.: 7 am - 5 pm (PST)

Tel: (800) 866-8608

Fax: (408) 922-9179

http://www.fujitsumicro.com/

Europe

FUJITSU MIKROELEKTRONIK GmbH

Am Siebenstein 6-10

D-63303 Dreieich-Buchschlag

Germany

Tel: (06103) 690-0

Fax: (06103) 690-122

Any semiconductor devices have inherently a certain rate 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.

http://www.fujitsu-ede.com/

Asia Pacific

FUJITSU MICROELECTRONICS ASIA PTE LTD

#05-08, 151 Lorong Chuan

New Tech Park

Singapore 556741

Tel: (65) 281-0770

If any products described in this document represent goods or

technologies subject to certain restrictions on export under the

Foreign Exchange and Foreign Trade Control Law of Japan, the

prior authorization by Japanese government should be required

for export of those products from Japan.

Fax: (65) 281-0220

http://www.fmap.com.sg/

F9803

FUJITSU LIMITED Printed in Japan

32


型号：	MB3785APFV
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）稳压器开关式稳压器或控制器电源电路开关式控制器
文件：	总29页 (文件大小：284K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

MB3785APFV [FUJITSU]

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