MB3789_技术文档

FUJITSU SEMICONDUCTOR

DATA SHEET

DS04-27211-3E

ASSP For Power Supply Applications

BIPOLAR

Switching Regulator Controller

(Supporting External Synchronization)

MB3789

■ DESCRIPTION

The MB3789 is a PWM (pulse width modulation) switching regulator controller supporting an external sync signal.

The MB3789 incorporates two error amplifiers which can be used respectively for voltage control and current

control, allowing the IC to serve as a DC/DC converter with current regulating functions.

The MB3789 is the ideal IC for supplying power to the back-lighting fluorescent tube for a liquid crystal display

(LCD) device such as a camera-integrated VTR.

■ FEATURES

• Wide range of operating power supply voltages: 3 V to 18 V

• Low current consumption: 1.5 mA (Typ.)

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

• Built-in two error amplifier

• Oscillator capable of operating with an external sync signal

• Built-in timer latch short protection circuit

• Variable dead time provides control over total operating range

• Output supporting a power MOSFET

• 16-pin SSOP package mountable at high density

■ PACKAGE

16-pin Plastic SSOP

(FPT-16P-M05)

MB3789

■ PIN ASSIGNMENT

(TOP VIEW)

V^CC1

V^REF

C T

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

GND

OUT

V^CC2

CB

SYNC

SCP

DTC

FB1^*1

FB2 ^*2

−IN2^*2

+IN2^*2

−IN1^*1

+IN1^*1

(FPT-16P-M05)

*1: Pins on error amplifier 1

*2: Pins on error amplifier 2

2

MB3789

■ PIN DESCRIPTION

Pin no.

Pin symbol

I/O

Function

Error amplifier 1 inverting input pin

7

8

–IN1

+IN1

FB1

I

Error amplifier 1 noninverting input pin

Error amplifier 1 output pin

6

O

I

10

9

–IN2

+IN2

FB2

Error amplifier 2 inverting input pin

Error amplifier 2 noninverting input pin

Error amplifier 2 output pin

I

11

O

Output bootstrap pin.

Connect a capacitor between the CB and OUT pins to bootstrap the

output transistor.

13

CB

—

5

SCP

DTC

OUT

—

I

Capacitor connection pin for short-circuit protection circuit

Dead time control pin

12

15

O

Totem-pole output pin

Sawtooth waveform frequency setting capacitor/resistor connection

3

4

C^T

—

I

SYNC

External sync signal input pin

1

14

2

V^CC1

V^CC2

V^REF

—

O

Reference power supply, control circuit power-supply pin

Output circuit power-supply pin

Reference voltage output pin

16

GND

—

Ground pin

3

MB3789

■ BLOCK DIAGRAM

CB

13

14

Error amp. 1

PWM comparator

+IN1

−IN1

FB1

8

7

6

V^CC2

OUT

15

Error amp. 2

10 kΩ

+IN2

−IN2

9

10

FB2 11

12

DTC

−0.9 V

−0.3 V

8 µA

4 µA

SCP comparator 1

1.25 V

SCP comparator 3

1.25 V

2 µA

VREF

SCP comparator 2

1

2

V^CC1

1.1 V

1.8 V

Under voltage

Lock-out

protection

circuit

Reference Power

Sawtooth

wave

oscillator

SR latch

voltage

supply

ON/OFF

circuit

V^REF

16

5

4

3

GND

SCP

SYNC

C^T

External sync signal

4

MB3789

■ FUNCTIONAL DESCRIPTION

1. Switching Regulator Functions

(1) Reference voltage generator

The reference voltage generator uses the voltage supplied from the power supply pin (pin 1) to generate a

temperature-compensated, referencevoltage(about2.50V)asthereferencesupplyvoltagefortheIC’sinternal

circuitry.

The reference voltage can be output, up to 50 µA, to an external device through the V^REFpin (pin 2).

This regulated reference voltage can be used as the reference voltage for the switching regulator and also

used for setting the dead time.

(2) Sawtooth waveform oscillator

With a timing capacitor and a timing resistor connected to the C^Tpin (pin 3), the sawtooth waveform oscillator

generates a sawtooth wave which remains stable even with supply voltage variations or temperature changes.

The sawtooth wave is input to the PWM comparator. The amplitude of oscillating waveform is 0.3 V to 0.9 V.

In addition, the oscillator can be used for external synchronization, where it generates a sawtooth waveform

synchronous to the input signal from the SYNC pin (pin 4).

(3) Error amplifiers

The error amplifiers detect the output voltage from the switching regulator and outputs the PWM control signal.

Since they support a wide range of in-phase input voltages from –0.2 V to “V^CC– 1.8 V”, they can be set easily

from an external power supply.

An arbitrary loop gain can be set by connecting a feedback resistor and capacitor from the error amplifier output

pin to the inverting input pin, enabling stable phase compensation to the system.

The MB3789 can make a current-regulated DC/DC converter using the two internal error amplifiers respectively

for voltage control and current control.

(4) PWM comparator

The PWM comparator is a voltage comparator with one inverting input and three noninverting inputs, serving

as a voltage-pulse width converter for controlling the output duty depending on the input voltage.

The PWM comparator turns on the output transistor during the interval in which the sawtooth wave voltage

level is lower than the voltage levels at all of the error amplifier output pins, the SCP pin (pin 5), and at the

DTC pin (pin 12).

(5) Output circuit

The output circuit is a power MOSFET driven, output circuit in a totem-pole configuration. It can drive the gate

voltage up to near the supply voltage with a bootstrap capacitor connected between the OUT pin (pin 15) and

CB pin (pin 13). (See “■ SETTING THE BOOTSTRAP CAPACITOR (C^BS).”)

2. Protection Functions

(1) Timer-latch short-circuit protection circuit

SCP comparator 1 detects the output voltage levels of error amplifiers 1 and 2. When the output voltage level

of either (or both) of the two error amplifiers reaches 1.25 V, the timer circuit is actuated to start charging the

external protection-enable capacitor connected to the SCP pin (pin 5).

If the error amplifier output is not restored to the normal voltage level before the capacitor voltage reaches

1.8 V, the latch circuit is actuated to turn off the output transistor while making the dead time 100%.

To reset the actuated protection circuit, turn the power supply on back. (See “■ SETTING THE SOFT START/

SHORT-CIRCUIT DETECTION TIME.”)

5

MB3789

(2) Low input voltage malfunction preventive circuit

The transient state or a momentary decrease in supply voltage, which occurs when the power supply is turned

on, may cause errors in the control IC, resulting in breakdown or degradation of the system. The low input

voltagemalfunctionpreventivecircuitdetectstheinternalreferencevoltagelevelaccordingtothesupplyvoltage

level and, if the input voltage is low, turn off the output transistor and maintains the SCP pin (pin 5) at 0 V while

making the dead time 100%.

The circuit restores voltage supply when the supply voltage reaches its threshold voltage.

6

MB3789

■ ABSOLUTE MAXIMUM RATINGS

(Ta = +25°C)

Rating

Parameter

Symbol

Condition

Unit

Min.

—

Max.

20

Power supply voltage

Power dissipation

V^CC

P^D

—

V

mW

°C

—

440*

+85

Ta +25°C

Operating temperature

Storage temperature

Top

Tstg

—

–30

–55

+125

°C

* : When mounted on a 10 cm-square double-side epoxy board.

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.

5.0

Parameter

Symbol

Condition

Unit

Min.

3.0

—

Max.

18

V^CC1

V^CC2

—

V

Power supply voltage

6.0

18

Reference voltage output

current

I^OR

—

–50

–30

—

µA

Error amp. input voltage

V^I

—

–0.2

–70

—

V^CC– 1.8

—

V

I^O+

–40

mA

CB = 4700 pF, t 2 µs

Output current

I^O–

R^T

—

10

40

39

70

200

6800

200

+85

mA

kΩ

pF

CB = 4700 pF, t 2 µs

Timing resistance

—

Timing capacitance

Oscillation frequency

Operating temperature

C^T

470

1

1000

20

f^OSC

T^OP

kHz

°C

–30

+25

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.

7

MB3789

■ ELECTRICAL CHARACTERISTICS

(V^CC1 = 5 V, V^CC2 = 6 V, Ta = +25°C)

Value

Unit

Parameter

Symbol

Condition

I^OR= 0 µA

Min.

Typ.

Max.

Output voltage

V^REF

2.400

2.500

2.600

V

Output voltage

temperature

variation

∆V^REF/V^REFTa = –30°C to +85°C*

—

0.2

2

%

Reference

voltage block

Input stability

Line

Load

I^OS

V^CC= 3.0 V to 18 V

—

1

10

mV

µA

V

Load stability

I^OR= 0 µA to –50 µA

2

Short output current

V^REF= 0 V

–700

—

–450

2.15

1.90

250

1.4

–300

2.62

—

V^TH

V^TL

—

Under

Threshold voltage

voltage

lockout

protection

circuit

—

1.62

80

V

Hysteresis width

Reset voltage (V^CC)

Charge current

V^HYS

V^R

—

mV

V

1.0

—

I^CHG

V^T0

V^SCP0.9 V

Duty cycle = 0%

Duty cycle = 100%

—

–2.8

0.2

–2.0

0.3

–1.2

0.4

1.0

1.90

µA

V

Soft start

block

Threshold voltage

V^T100

V^TH

0.8

0.9

V

1.70

1.80

V

Input standby

voltage

Short circuit

detection

block

V^STB

—

1.15

1.25

1.35

mV

Input latch voltage

Input source current

V^I

I^I

—

50

100

mV

V^SCP= 1.5 V

–8.4

–6.0

–3.6

µA

C^T= 1000 pF,

R^T= 39 kΩ

Oscillator frequency

f^OSC

17

—

20

1

23

10

kHz

%

Frequency voltage

variation

∆f/f^dv

V^CC= 3 V to 18 V

Triangular

waveform

oscillator

block

Frequency

temperature

variation

∆f/f^dT

Ta = –30°C to +85°C*

—

3

—

%

Synchronous pin

input current

I^SYNC

V^THSY= 5 V

—

0.9

1.3

2.2

mA

V

Synchronous pin

threshold voltage

V^THSY

0.65

0.75

0.85

* : Standard design value

(Continued)

8

MB3789

(Continued)

(V^CC1 = 5 V, V^CC2 = 6 V, Ta = +25°C)

Value

Unit

Parameter

Symbol

Condition

V^FB= 0.6 V

Min.

—

Typ.

—

Max.

10

Input offset voltage

Input offset current

Input bias current

V^IO

I^IO

I^B

mV

nA

V^FB= 0.6 V

—

100

—

–200

–30

Common mode

input voltage range

V^CM

—

–0.2

—

V^CC– 0.8

V

Common mode

rejection ratio

C^MRR

A^V

—

60

—

100

800

—

dB

Error

amplifier

Voltage gain

Frequency

bandwidth

BW

A^V= 0 dB*

kHz

V^OM+

V^OM–

I^OM+

—

V^REF– 0.3

2.4

0.05

60

—

0.3

—

V

Maximum output

voltage range

—

Output sink current

V^FB= 0.6 V

30

µA

Output source

current

I^OM–

V^FB= 0.6 V

—

–2

–0.6

mA

V^T0

V^T100

Dtr

Duty cycle = 0%

Duty cycle = 100%

V^dt= V^REF/4.2

—

0.2

0.8

45

0.3

0.9

55

0.4

1.0

65

V

Threshold voltage

Dead time

control block

ON duty cycle

%

Input bias current

I^Ibdt

–500

0.2

0.8

30

–100

0.3

0.9

60

—

nA

V

V^T0

Duty cycle = 0%

Duty cycle = 100%

—

0.4

1.0

—

Threshold voltage

PWM

comparator

block

V^T100

I^IN+

V

Input sink current

µA

mA

Input source current

I^IN–

—

–2

–0.6

CL = 2000 pF,

CB = 4700 pF

V^OH

V^OL

5.5

—

6.0

1.1

—

V

Output block Output voltage

Power supply

CL = 2000 pF,

CB = 4700 pF

1.4

I^CC1

I^CC2

—

1.15

350

1.65

500

mA

General

current when output

off

µA

* : Standard design value

9

MB3789

■ TYPICAL CHARACTERISTICS

Power supply current vs.

power supply voltage characteristics

2.4

Output power supply current vs.

power supply voltage characteristics

500

400

300

200

100

0

V^CC1 = 5 V

VCC2 = 6 V

Ta = +25°C

2.0

Ta = +25°C

1.6

1.2

0.8

0.4

0

4

8

12

16

20

0

4

8

12

16

20

Power supply voltage V^CC1 (V)

Power supply voltage V^CC2 (V)

Reference voltage vs.

power supply voltage characteristics

Reference voltage vs.

ambient temperature characteristics

2.56

2.54

2.52

2.50

2.48

2.46

2.44

5.0

4.0

3.0

2.0

1.0

0

VCC1 = 5 V

V^CC2 = 6 V

I^OR= 0 µA

V^CC2 = 6 V

I^OR= 0 µA

Ta = +25°C

0

4

8

12

16

20

−40 −20

0

20

40

60

80

100

Power supply voltage V^CC1 (V)

Ambient temperature Ta (°C)

Sawtooth waveform maximum amplitude voltage vs.

timing capacitance characteristics

Sawtooth wave frequency vs.

timing resistance characteristics

(With C^T/RT oscillation)

(With CT/RT oscillation)

500 k

1.4

V^CC1 = 5 V

V^CC2 = 6 V

VCC1 = 5 V

VCC2 = 6 V

SYNC = GND

Ta = +25°C

1.2

R^T= 39 kΩ

100 k

50 k

SYNC = GND

Ta = +25°C

1.0

0.8

0.6

0.4

0.2

0

10 k

5 k

CT = 470 pF

1 k

C^T= 1500 pF

C^T= 4700 pF

500

C^T= 6800 pF

100

2 k

10²

5 × 10²10³5 × 10³10⁴

5 × 10⁴

5 k 10 k

50 k 100 k

500 k 1 M

Timing capacitance CT (pF)

Timing resistance R^T(Ω)

(Continued)

10

MB3789

Sawtooth waveform period vs.

timing capacitance characteristics

(With C^T/RT oscillation)

Duty vs. sawtooth wave

frequency characteristics

(With C^T/RT oscillation)

100

500

VCC1 = 5 V

V^CC2 = 6 V

V^DT= 0.6 V

C^T= Variable

RT = 39 kΩ

SYNC = GND

Ta = −25°C

80

60

40

20

VCC1 = 5 V

V^CC2 = 6 V

R^T= 39 kΩ

SYNC = GND

Ta = +25°C

100

50

10

5

2

0

2 × 10 5 × 10 10²5 × 10²10³

5 × 10³10⁴

5 × 10⁴

200 500 1 k

5 k 10 k

50 k 100 k

500 k

Timing capacitance CT (pF)

Sawtooth wave frequency f (Hz)

Sawtooth wave frequency vs.

ambient temperature characteristics

(With C^T/RT oscillation)

Sawtooth wave frequency vs.

ambient temperature characteristics

(In external synchronization)

V^CC1 = 5 V

V^CC2 = 6 V

C^T= 1500pF

RT = 39 kΩ

V^CC1 = 5 V

V^CC2 = 6 V

C^T= 1500pF

RT = 43 kΩ

+10

+5

0

+10

+5

0

SYNC = GND

f^SYNC= 15.0 kHz

−5

10

−5

−10

−40

−20

0

20

40

60

80

100

−40 −20

0

20

40

60

80

100

Ambient temperature Ta (°C)

Gain vs. frequency and phase vs.

frequency characteristics

Measurement circuit for gain-frequency

characteristics and phase-frequency characteristics

2.5 V 2.5 V

V^CC1 = 5 V

V^CC2 = 6 V

Ta = +25°C

40

20

180

90

240 kΩ

Av

4.7 kΩ

0

OUT

10 µF

φ

Error amp.

IN

−20

−40

−90

−180

4.7 kΩ

1 k

10 k

100 k

1 M

10 M

Frequency f (Hz)

(Continued)

11

MB3789

(Continued)

Duty vs. DTC pin voltage characteristics

Output pin (OUT) voltage and current waveforms

V^CC1 = 5 V,

V^CC2 = 6 V

100

80

60

40

20

0

V^CC1 = 5 V

V^CC2 = 6 V

C^T= 1500 pF

RT = 39 kΩ

SYNC = GND

6

4

2

100

0

50

0

−50

−100

0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

DTC pin voltage Vdt (V)

0

4

8

12

16

20

Time t (µs)

Power comsumption vs.

ambient temperature characteristics

500

440

400

300

200

100

0

−30 −20

0

20

40

60

80

100

Ambient temperature Ta (°C)

12

MB3789

■ SETTING THE OUTPUT VOLTAGE

Set the output voltage by connecting the input pins (+IN, –IN) and output pin (FB) of error amplifiers 1 and 2 as

shown in Figures 1 and 2.

V^REF

+

VOUT

V^REF

+

V^OUT

=

(R1 + R2)

R

R1

R2

2 × R2

RNF

Figure 1 Setting the output voltage (positive output voltage (V^OUT))

V^REF

VREF

R1

R2

R

−

V^OUT= −

(R1 + R2) + VREF

2 × R1

RNF

−

VOUT

Figure 2 Setting the output voltage (negative output voltage (V^OUT))

13

MB3789

■ CONNECTION FOR OUTPUT CONTROL WITH ONE ERROR AMPLIFIER

The MB3789 can make up a system using only one of the two error amplifiers. In this case, connect the +IN and

–IN pins of the unused error amplifier to the V^REFand GND pins, respectively, and leave the FB pin open.

When V^CC– 1.8 V < V^REF, divide the V^REFvoltage using a resistor and apply the voltage to the +IN pin.

VREF

2

+IN1

8

−IN1

7

FB1

6

“Open”

Figure 1 Connection without using error amplifier 1

VREF

2

+IN2

9

−IN2

10

FB2

11

“Open”

Figure 2 Connection without using error amplifier 2

14

MB3789

■ CONNECTING THE SAWTOOTH WAVEFORM OSCILLATOR

1. Connection for internal oscillation

For internal oscillation, connect the frequency setting capacitor (C^T) and resistor (R^T) to the C^Tpin (pin 3) and

leave the SYNC pin (pin 4) open or connect it to GND.

The oscillation frequency can be set with the C^Tand R^Tconstants.

CT

SYNC

4

3

C^T

RT

Leave “open” or connect to GND

Figure 5 Connection for internal oscillation

2. Connection for external synchronous oscillation

For external synchronous oscillation, connect the frequency setting capacitor (C^T) and resistor (R^T) to the C^Tpin

(pin 3) and connect the external sync signal to the SYNC pin (pin 4).

In this case, select the C^Tand R^Tconditions so that the oscillation frequency is 5% to 10% lower than the

frequency of the external sync signal excluding the setting error of the oscillation frequency.

CT

SYNC

4

3

External sync signal

C^T

RT

Figure 6 Connection for external synchronous oscillation

15

MB3789

■ SETTING THE DEAD TIME

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

to a full-ON state (ON duty = 100%) when the power supply is turned on. To prevent this problem, you may

determine the voltage at the DTC pin (pin 12) from the V^REFvoltage so you can set the output transistor’s dead

time (maximum ON-duty period) as shown in Figure 7 below.

1. Setting the dead time

When setting the dead time, use resistors as shown in Figure 7 to connect the V^REFand DTC pins to GND. When

the voltage at the DTC pin (pin 12) is lower than the sawtooth wave output voltage from the oscillator, the output

transistor is turned off.

To set the dead time, see “Duty vs. DTC pin voltage” (in “■ STANDARD CHARACTERISTIC CURVES”).

R2

R1 + R2

V^dt=

× V^REF

2. Connection without setting the dead time

If you do not set the dead time, connect the V^REFand DTC pins as shown in Figure 8.

V^REF

DTC

2

R1

R2

12

V^dt

Figure 7 Connection for setting the dead time

V^REF

DTC

2

12

Figure 8 Connection without setting the dead time

16

MB3789

■ SETTING THE SOFT START/SHORT-CIRCUIT DETECTION TIME

Connecting capacitor C^PEto the SCP pin (pin 5) as shown in Figure 9 enables a soft start and short-circuit

protection.

8 µA

4 µA

SCP comparator 1

1.25 V

Output OFF

SCP comparator 3

1.25 V

SCP comparator 2

2 µA

V^REF

1.1 V

1.8 V

Low input

voltage

protection

circuit

SR latch

5

SCP

C^PE

Figure 9 Soft start/short-circuit detection circuit

2

1

0

1.8 V

1.25 V

Output short-circuit

t^PE

Output short-circuit

100%

50%

t^s

0%

Soft start

Time t (s)

Figure 10 SCP pin operating waveform

17

MB3789

1. Soft Start

To prevent surge currents when the IC is turned on, you can set a soft start by connecting capacitor C^PEto the

SCP pin (pin 5).

~

• Softstart time(ts): Time required up to duty cycle 50% with output on

~

t^S(s) 0.15 × C^PE(µF)

2. Protection from short circuit

SCP comparator 1 always compares the output voltage levels at error amplifiers 1 and 2 with the 1.25 V

reference voltage.

When the load conditions for the switching regulator are stable, the outputs from error amplifiers 1 and 2 do

not vary and thus short-circuit protection control remains balanced. In this case, the SCP pin (pin 5) is held at

the soft start end voltage (about 1.25 V).

If the load conditions change rapidly and the output voltage of error amplifier 1 or 2 reaches 1.25 V, for example,

because of a short-circuit of a load, capacitor C^PEis charged further. When capacitor C^PEis charged up to about

1.8 V, the SR latch is set and the output drive transistor is turned off. At this time, the dead time is set to 100%,

~

capacitor C^PEis discharged, and the SCP pin becomes 50 mV.

• Short-circuit detection time (t^PE)

~

t^PE(s) 0.09 × C^PE(µF)

3. Connection without using short-circuit protection

Add a clamp circuit as shown in Figure 11 so that the clamp voltage (V^CRP) falls within the following range when

a short-circuit is detected: 1.0 V < V^CRP< 1.7 V

Clamp circuit

5

SCP

V^CRP

CPE

Figure 11 Connection without using short-circuit protection

18

MB3789

■ SETTING THE BOOTSTRAP CAPACITOR

When a bootstrap capacitor is connected, it raises the output-ON voltage (at the OUT pin (pin 15) when the

~

external MOS FET is turned “ON”) to the V^CC2 level. It can therefore drive the MOS FET at a higher threshold

voltage (V^th).

1. Connecting the bootstrap capacitor

Connect the bootstrap capacitor between the CB pin (pin 13) and OUT pin (pin 15).

VCC2

VCBS

id

CB

13

14

V^CC2

VCC1

CBS

iC

External

MOS FET

I

15

OUT

10 kΩ

VOUT

: Charge current ic

: Discharge current id

Figure 12 Circuit with a bootstrap capacitor connected and current flow

• Calculation of bootstrap capacitance

500 × 10⁶

V^CC2 – 2.6

C^BS

× t^ON(max) [pF]

t^ON(max): Maximum ON duty time

19

MB3789

2. Connection with no bootstrap capacitor

Connect the CB pin (pin 13) and V^CC2 pin (pin 14) as shown in Figure 13.

VCC2

CB

13

14

15

V^CC2

External

MOS FET

OUT

Note: Under a condition of “V^CC2 − Vth < 1.1 V”, bootstrap capacitor CBS should be connected because

the external MOS FET cannot be driven sufficiently.

V^th: External MOS FET threshold voltage

Figure 13 Connection with no bootstrap capacitor connected

20

MB3789

3. Operation of the Bootstrap Capacitor

When voltage V^OUTat the OUT pin (pin 15) is “L” level, the voltages (V^C1) at both ends of the bootstrap capacitor

C^BSis charged up to the V^CC2 voltage level by charge current (i^C).

~

When V^OUTchanges from “L” level to “H” level, the CB pin (pin 13) voltage V^CBSrises to 2 × V^CC2 and V^OUT

reaches almost the V^CC2 level.

The charge accumulated at C^BSat this time is released by discharge current i^d(output unit supply current).

See Figure 12 for circuit operation.

(V^CC1 = 5 V, VCC2 = 6 V, CBS = 4700 pF)

2 V

12

*2

10

8

*1

V^CBS

6

4

2

0

6

4

2

0

VOUT

2 V

10 µs

0

20

40

60

80

100

tON

tOFF

Time t (µs)

*1: Use the device with a setting of VCBS 18 V.

*2: The slant of V^CBSis determined by the value of discharge current id (output unit supply current).

Figure 14 Bootstrap operating waveform

21

MB3789

■ EQUIVALENT SERIES RESISTANCE OF SMOOTHING CAPACITOR AND SYSTEM

STABILITY

The equivalent series resistance (ESR) value of a smoothing capacitor for the DC/DC converter largely affects

the loop phase characteristic.

Depending on the ESR value, the phase characteristic causes the ideal capacitor in a high-frequency domain

advance the loop phase (as shown in Figures 16 and 17) and thus the system is improved in stability. In contrast,

using a smoothing capacitor with low ESR lowers system stability. Use meticulous care when a semiconductor

electrolytic capacitor with low ESR (such as an OS capacitor) or a tantalum capacitor is used. (The next page

gives an example of reduction in phase margin when an OS capacitor is used.)

L

Tr

RC

VIN

D

RL

C

Figure 15 Basic circuit of step-down DC/DC converter

20

0

(2)

−90

−20

−40

−60

(2)

(1) : RC = 0 Ω

(1)

(1) : R^C= 0 Ω

(2) : R^C= 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

Figure 16 Gain vs. frequency

Figure 17 Phase vs. frequency

22

MB3789

(Reference data)

Changing the smoothing capacitor from an aluminum electrolytic capacitor (R^C1.0 Ω) to a low-ESR

~

semiconductor electrolytic capacitor (OS capacitor: R^C0.2 Ω) halves the phase margin. (See Figures 19 and

20.)

VOUT

+

VO

C^NF

AV-phase characteristic

in this range

−IN

VIN

FB

+IN

R²

R¹

VREF/2

Error amplifier

Figure 18 DC/DC converter Av vs. phase measurement diagram

AI electrolytic capacitor gain vs. frequency, phase vs. Frequency (DC/DC converter +5 V output)

60

V^CC= 10 V

RL = 25 Ω

CP = 0.1 µF

40

20

180

90

A^V

+

VO

φ

AI electrolytic capacit

220 µF (16 V)

R^C1.0 Ω: fOSC = 1 kHz

62°

0

−90

−180

−20

−40

GND

10

100

1 k

Frequency f (Hz)

10 k

100 k

Figure 19 Gain vs. frequency

23

MB3789

OS capacitor gain vs. frequency, phase vs. frequency (DC/DC converter +5 V output)

60

V^CC= 10 V

RL = 25 Ω

A^V

40

20

180

90

C^P= 0.1 µF

+

V^O

OS capacitor

22 µF (16 V)

φ

0

R^C0.2 Ω: fOSC = 1 kHz

27°

−90

−180

−20

−40

GND

10

100

1 k

10 k

100 k

Frequency f (Hz)

Figure 20 Phase vs. frequency characteristic curves

24

MB3789

■ APPLICATION EXAMPLE

10 µH

10 µF

V^CC

(5 V)

2

1

V^REF

VCC1

V^CC2

100 kΩ

14

13

8

+IN1

18 kΩ

CB

7

6

−IN1

2.7 kΩ

100 kΩ

FB1

4700 pF

150 kΩ

100 kΩ

+IN2

9

MB3789

Back

light

15

OUT

10

11

12

−IN2

10 kΩ

100 kΩ

FB2

150 kΩ

100 kΩ

10 µF

GND 16

DTC

SYNC

C^T

3

SCP

5

4

1 µF

39 Ω

22 kΩ

33 pF

4.7 kΩ

1500 pF

4.7 µF

33 kΩ

Synchronous signal

25

MB3789

■ USAGE PRECAUTIONS

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.

If a voltage greater than the maximum value is input to 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 MΩ placed in series between the human body and earth.

■ ORDERING INFORMATION

Part number

MB3789PFV

Package

Remarks

16-pin Plastic SSOP

(FPT-16P-M05)

26

MB3789

■ PACKAGE DIMENSION

16-pin Plastic SSOP

(FPT-16P-M05)

*: These dimensions do not include resin protrusion.

1.25^–⁺⁰⁰^.^.¹²⁰⁰

*

5.00±0.10(.197±.004)

(Mounting height)

.049⁺^–.^.⁰⁰⁰⁰⁴⁸

0.10(.004)

INDEX

*

4.40±0.10

6.40±0.20

5.40(.213)

NOM

(.173±.004) (.252±.008)

"A"

0.22^–⁺⁰⁰^.^.⁰¹⁵⁰

.009^–⁺^.^.⁰⁰⁰⁰²⁴

0.15^–⁺⁰⁰^.^.⁰⁰²⁵

Details of "A" part

0.65±0.12

(.0256±.0047)

.006^–⁺^.^.⁰⁰⁰⁰¹²

0.10±0.10(.004±.004)

(STAND OFF)

0

10°

0.50±0.20

(.020±.008)

4.55(.179)REF

Dimensions in mm (inches)

C

1994 FUJITSU LIMITED F16013S-2C-4

27

MB3789

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: 81(44) 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: 81(44) 754-3329

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

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.

North and South America

FUJITSU MICROELECTRONICS, INC.

Semiconductor Division

3545 North First Street

San Jose, CA 95134-1804, USA

Tel: (408) 922-9000

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.

Fax: (408) 922-9179

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 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.

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 Law of Japan, the prior

authorization by Japanese government will be required for

export of those products from Japan.

Fax: (65) 281-0220

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

F9906

FUJITSU LIMITED Printed in Japan

28


型号：	MB3789
厂家：	FUJITSU
描述：	Switching Regulator Controller (Supporting External Synchronization) 开关稳压器控制器（支持外部同步）稳压器开关控制器
文件：	总28页 (文件大小：205K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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