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FA7703/04

1.This Data Book contains the product specifications, characteristics, data, materials, and structures as of

June 2002. The contents are subject to change without notice for specification changes or other
reasons. When using a product listed in this Data Book, be sure to obtain the latest specifications.

2. All applications described in this Data Book exemplify the use of Fuji's products for your reference only.

No right or license, either express or implied, under any patent, copyright, trade secret or other
intellectual property right owned by Fuji Electric Co., Ltd. is (or shall be deemed) granted. Fuji makes
no representation or warranty, whether express or implied, relating to the infringement or alleged
infringement of other's intellectual property rights, which may arise from the use of the applications,
described herein.

3. Although Fuji Electric is enhancing product quality and reliability, a small percentage of semiconductor

products may become faulty. When using Fuji Electric semiconductor products in your equipment, you
are requested to take adequate safety measures to prevent the equipment from causing a physical
injury, fire, or other problem if any of the products become faulty. It is recommended to make your
design fail-safe, flame retardant, and free of malfunction.

4.The products introduced in this Data Book are intended for use in the following electronic and electrical

equipment, which has normal reliability requirements.

· Computers · OA equipment · Communications equipment (terminal devices)
· Measurement equipment · Machine tools · Audiovisual equipment · Electrical home appliances
· Personal equipment · Industrial robots etc.

5.If you need to use a product in this Data Book for equipment requiring higher reliability than normal,

such as for the equipment listed below, it is imperative to contact Fuji Electric to obtain prior approval.
When using these products for such equipment, take adequate measures such as a backup system to
prevent the equipment from malfunctioning even if a Fuji's product incorporated in the equipment
becomes faulty.
· Transportation equipment (mounted on cars and ships) · Trunk communications
equipment
· Traffic-signal control equipment · Gas leakage detectors with an auto-shut-off feature
· Emergency equipment for responding to disasters and anti-burglary devices · Safety devices

6. Do not use products in this Data Book for the equipment requiring strict reliability such as (without

limitation)
· Space equipment · Aeronautic equipment · Atomic control equipment
· Submarine repeater equipment · Medical equipment

reproduced in any form or by any means without the express permission of Fuji Electric.

8. If you have any question about any portion in this Data Book, ask Fuji Electric or its sales agents

before using the product. Neither Fuji nor its agents shall be liable for any injury caused by any use of
the products not in accordance with instructions set forth herein.

WARNING

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FA7703/04

CONTENTS

Page

1. Description ......................................................... 4

2. Features ............................................................. 4

3. Outline ................................................................ 4

4. Block diagram ..................................................... 5

5. Selection Guide.................................................... 5

6. Pin assignment ................................................... 5

7. Ratings and characteristics ................................ 6

8. Characteristics curves.......................................... 9

9. Description of each circuit .................................. 13

10. Design advice ..................................................... 16

11. Application circuit ............................................... 21

Note

· Parts tolerance and characteristics are not defined in all application described in this Data book. When

design an actual circuit for a product, you must determine parts tolerances and characteristics for safe and
stable operation.

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FA7703/04

Description

FA7703/04 are the PWM type DC-DC converter control ICs with 2ch output that can directly drive power

MOSFETs. FA7703/04 feature CMOS devices with high breakdown voltage and also low power
consumption are achieved. By means of their small and thin package (1.1mm max.), and high frequency
operation (to 1MHz), FA7703/04 are completely suitable for the use of very small DC-DC converters.
Besides, you can select a Pch or Nch type of MOSFET directly driven by FA7703/04, and also you can
practically design any kind of DC-DC converter circuit like a boost converter, a buck converter, a inverting
converter, a fly-back converter, and so on.

1. Features

Wide range of supply voltage: VCC=2.5 to 20V

Direct driving of MOSFET

Switching Pch/Nch driving is available (channel 1 only)

Low current consumption is achieved by CMOS process:
1.8mA (typ.) in operation

2ch PWM control IC

High frequency operation is available: 50kHz to 1MHz

Simple setting of operation frequency with a timing resistor

Soft start setting is available

Setting of the limitation of maximum output duty cycle is available in each channel

Built-in protection function for undervoltage lockout

Highly accurate reference voltage:
VREF: 1.00V

1%, VB: 1.00V

2%, VREG: 2.20V

Built-in output timer latched short-circuit protection circuit

Thin and small package: TSSOP-16, SOP-16

2. Outline

TSSOP-16 (V) SOP-16 (M)

7
1

.
1

.
3

0.4 ±0.05

1.27

.
2

10.2 ±0.3

.
0
5

0.65

.
1

5.0 ±0.1

units:mm

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FA7703/04

3.Block diagram

4. Selection Gide

Ch.1(OUT1)

Buck, Boost, Fly-back

FA7703

Ch.2(OUT2)

Buck, Inverting (Pch driven)

Ch.1(OUT1)

Buck, Boost, Fly-back

FA7704

Ch.2(OUT2)

Boost, Fly-back (Nch driven)

5. Pin assignment

Pin No

symbol

Description

Oscillator timing resistor

Soft start, Timer latched short circuit protection, ON/OFF control

3 DT2

Ch.2

Dead Time Adjustment

IN2+

Ch.2 non-inverting input to error amplifier

IN2-

Ch.2 inverting input to error amplifier

FB2

Ch.2 output o error amplifier

7 GND

Ground

8 OUT2

Ch.2

output

9 VCC

Power

supply

10 OUT1

Ch.1

output

SEL

Selection of type of driven MOSFET (OUT1)

FB1

Ch.1 output o error amplifier

IN1-

Ch.1 inverting input to error amplifier

14 REF

Reference

voltage

15 DT1

Ch.1

Dead Time Adjustment

16 REG

Regulated

voltage

output

REG

DT1

REF

IN1-

FB1

SEL1

OUT1

VCC

DT2

IN2+

IN2-

FB2

GND

OUT2

OSC

Power G ood Signal

Reference

voltage

UVLO

BIAS

Er.Am p1

Er.Am p2

PW M.Com p1

PW M.Com p2

1.5V

2.0V

1.3V

S.C.DET

S.C.P

O N/O FF

BIAS

2.2V

FA7704

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FA7703/04

6.Ratings and characteristics

The contents are subject to change without notice. When using a product, be sure to obtain the latest
specifications.

(1)Absolute maximum ratings

Item Symbol

Ratings

Units

Power supply voltage

20 V

REF Terminal output current

REF

1 mA

REG Terminal output current

REG

2 mA

SOpeak

-400(peak) mA

OUT1, OUT2 Terminal source current

SOcont

-50(continuos) mA

SIpeak

+150(peak) mA

OUT1, OUT2 Terminal sink current

SIcont

+50(continuos) mA

RT,CS,REG,REF,IN1-,IN2+,IN2-,FB1,
FB2,DT1,DT2,SEL1 Terminal voltage

LOGIC

+2.5(max.)

-0.3(min.)

TSSOP 300

Power dissipation
(Ta25

C)*

SOP

400

Operating ambient temperature

-30 to +85

°C

Operating junction temperature

+125 °C

Storage temperature

stg

-40 to +150

°C

*:Maximum dissipation curve at Ta25

C is shown under figure.

(2)Recommended operating conditions

Item Symbol

MIN.

TYP.

MAX.

Units

Supply voltage

2.5 6 18 V

DC feedback resistor of
error amplifier

100

VCC terminal capacitance*

VCC

0.1

REG terminal capacitance

REG

0.047 0.1

CS terminal capacitance

0.01

Oscillation frequency

OSC

50 1000 kHz

Pch,PNP driving

SEL1L

Connect

GND

SEL1 terminal
voltage

Nch,NPN driving

SEL1H

Connect to REG terminal

*Please select the proper value by input-output conditions of power supply.

Maximum power dissipation curve

100

200

300

400

500

-30

120

150

Ambient temperature Ta[°C]

Maximum power dissipation Pd[mW]

TSSO

SOP

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FA7703/04

(3)Electrical characteristics

[Unless otherwise standard,Ta=25

C,Vcc=6V,R

=22k

]

(1) Internal Bias Section (REF terminal voltage)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

Output Voltage

REF

REF terminal load current
I

REF

=0mA

0.990 1.000 1.010 V

Line Regulation

LINEF

Vcc=2.5

18V,I

REF

=0mA

±1

±5

Load Regulation

LDF

IREF=0

1mA

-10

-3

Variation
with temperature

TCF

Ta=-30 to +85

Change rate for value at 25

-0.8 to

+0.2

(2) Regulated Voltage for Internal Control Blocks Section (REG terminal voltage)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

Output Voltage

REG

REG terminal load current
I

REG

=0mA

2.156 2.200 2.244 V

Line Regulation

LINEG

Vcc=2.5

18V,I

REG

=0mA

±4

±14

Load Regulation

LDG

REG

=0 to 2mA

-12

-2

Variation
with temperature

TCG

Ta=-30 to +85

Change rate for value at 25

-0.8 to

+0.2

(3) Oscillator Section

Item Symbol Conditions MIN.

TYP.

MAX.

Units

Oscillation frequency

OSC

=22k

160 190 220 kHz

Line Regulation

LINE

Vcc=2.5

18V

±0.1

TC1

Ta=+25 to -30

, f=50k to 1MHz

±2 %

Variation
With temperature

TC2

Ta=+25 to +85

, f=50k to1MHz

±3 %

(4) Error Amplifier Section (Input:IN1-,IN2+,IN2-,Output:FB1,FB2 terminal)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

Reference Voltage
(ch1)

IN1- terminal threshold voltage

0.980

1.000

1.020

Input offset (ch2)

OFST

(IN2+) - (IN2-)

±10

Common mode input
voltage

0.3 1.4 V

Input Current

-100 0 +100 nA

Open Loop Gain

Unity Gain Bandwidth

1.5 MHz

Output Source Current

OHE

FB1,2
terminal voltage=V

REF

-0.5V

-220 -160 -100

Output sink Current

OLE

FB1,2

terminal

voltage=0.5V

12 mA

(5) Pulse Width Modulation Section (FB1,FB2 terminal)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

Input threshold voltage

FB0

Duty

Cycle=0%

0.550 0.650 0.750 V

Input threshold voltage

FB100

Duty

Cycle=100%

1.000 1.100 1.200

(6) Dead Time Adjustment Circuit Section (DT1, DT2 terminal)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

Input threshold voltage

DT0

Duty

Cycle=0%

0.550 0.650 0.750 V

Input threshold voltage

DT100

Duty

Cycle=100%

1.000 1.100 1.200

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FA7703/04

(7) Under Voltage Lock-Out Section (VCC terminal)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

ON threshold

CCON

2.00 2.25

OFF threshold

CCOF

1.40 1.85

Hysteresis Voltage

CCHY

0.05 0.15 0.35

Ta=-30 to +25

+0.3 mV/°C

Variation
with temperature

CCHY

Ta=+25to +85

-0.1

mV/

(8) Soft Start Section (CS terminal)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

Output source current

CS=0V -2.8

-2.2

-1.6

Threshold Voltage1

CS0

Duty

Cycle=0%

0.550 0.650 0.750 V

Threshold Voltage2

CS50

Duty

Cycle=50%

0.880

(9) Short circuit Protection Section (FB terminal, CS terminal)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

Short Detection
Threshold Voltage

FBTH

FB terminal voltage

1.350

1.500

1.650

Latched Mode
Threshold Voltage

CSTH

CS terminal voltage

1.900

2.000

2.100

Latched Mode
Reset Voltage

CSRE

CS terminal voltage

1.830

Latched Mode
Hysteresis

CSHY

CS terminal voltage

170

300

CSCL1

FB terminal voltage<1.35V

1.200

1.270

1.340

CS terminal
Clamped Voltage

CSCL2

FB terminal voltage>1.65V

2.120

2.200

2.280

(10) Output Stage Section (OUT1,OUT2 terminal,SEL1 terminal)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

High side on resistance

ONH

=6V,Source Current=-50mA

High side on resistance

ONH

=2.5V,Source

Current=-50mA

18 36

Low side on resistance

ONL

=6V,Sink Current=+50mA

Low side on resistance

ONL

=2.5V,Sink

Current=+50mA 5 10

trn

330pF Load to GND terminal

Rise Time

trp

330pF Load to VCC terminal

tfn

330pF Load to GND terminal

Fall Time

tfp

330pF Load to VCC terminal

SEL1L

Pch-MOSFET,
PNP transistor driving

0 0.2

SEL1 terminal Input
Voltage

SEL1H

Nch-MOSFET,
NPN transistor driving

REG

0.2

REG

(11) Overall Section (VCC terminal)

Item Symbol Conditions MIN.

TYP.

MAX.

Units

CC0

Duty Cycle=0%,OUT1/2:open
CS=0V, FB1,FB2

REG

=22k

190kHz

1.3

1.9

CC1

Duty Cycle=80%,OUT1/2:open
R

=22k

190kHz

1.8

2.7

Operating mode
Supply Current

CC2

Duty Cycle=80%,OUT1/2:open
R

=3k

1MHz

3.1

4.7

Latched mode
Supply Current

CCLAT

CS>2.1V,FB1,FB2

REG

=22k

190kHz

1.3

1.9

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FA7703/04

7. Characteristics curves

Timing resistor vs.Oscillation frequency

100

1000

100

Timing resistor RT[k

]

Oscillation frequency [kHz]

Vcc=6V

Regulated voltage vs.Supply voltage VCC

2.18

2.19

2.20

2.21

2.22

Supply voltage Vcc[V]

Regulated voltage VREG[V

]

IREG=0A,RT=22k

Reference voltage vs.Supply voltage VCC

0.990

0.995

1.000

1.005

1.010

Supply voltage Vcc[V]

Reference voltage VREF[V

]

IREF=0A,RT=22k

Oscillation frequency vs.ambient temperature

185

186

187

188

189

190

191

192

193

194

195

-40

-20

100

Ambient temperature Ta[°C]

Oscillation frequency [kHz]

Vcc=6V,RT=22k

Regulated voltage vs.Ambient temperature

2.16

2.17

2.18

2.19

2.20

2.21

2.22

2.23

2.24

-40

-20

100

Ambient temperature Ta[°C]

Regulated voltage VREG[V

]

IREG=0A,RT=22k

Reference voltage vs.Ambient temperature

0.98

0.99

1.00

1.01

1.02

-40

-20

100

Ambient temperature Ta[°C]

Reference voltage VREF[V

]

IREF=0A,RT=22k

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FA7703/04

FB terminal voltage vs.Duty cycle

100

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

FB terminal voltage [V]

Duty cycle [%]

FA7703/04:OUT1 Nch driven (SEL1=REG)
FA7704:OUT2

fosc=1MHz

fosc=190kHz

DT terminal voltage vs.Duty cycle

100

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

DT terminal voltage [V]

Duty cycle [%]

fosc=1MHz

fosc=190kHz

FA7703/04:OUT1 Nch driven (SEL1=REG)
FA7704:OUT2

CS terminal voltage vs.Duty cycle

100

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

CS terminal voltage [V]

Duty cycle [%]

fosc=1MHz

fosc=190kHz

FA7703/04:OUT1 Nch driven (SEL1=REG)
FA7704:OUT2

FB terminal voltage vs.Duty cycle

100

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

FB terminal voltage [V]

Duty cycle [%]

fosc=1MHz

fosc=190kHz

FA7703/04:OUT1 Pch driven (SEL1=GND)
FA7703:OUT2

DT terminal voltage vs.Duty cycle

100

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

DT terminal voltage [V]

Duty cycle [%]

fosc=1MHz

fosc=190kHz

FA7703/04:OUT1 Pch driven (SEL1=GND)
FA7703:OUT2

CS terminal voltage vs.Duty cycle

100

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

CS terminal voltage [V]

Duty cycle [%]

fosc=1MHz

fosc=190kHz

FA7703/04:OUT1 Pch drivenb (SEL1=GND)
FA7703:OUT2

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FA7703/04

Duty cycle vs. Ambient temperature

-40

-20

100

Ambient temperature Ta[°C]

duty cycle [%]

DT terminal voltage

1.05V

fosc=190kHz

fosc=1MHz

FA7703/04:OUT1 Nch drive (SEL1=REG)
FA7704:OUT2

Operating mode supply current vs.Supply voltage

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Supply voltage Vcc[V]

Operating mode supply current [mA

]

Duty=80%,
IN(-)-FB:shorted

fosc=190kHz

fosc=1MHz

Operating supply current vs.Ambient temperature

1.0

1.5

2.0

2.5

-40

-20

100

Ambient temperature Ta[°C]

Operating supply current [mA]

Duty=80%

RT=22k

Vcc=6V

Duty cycle vs. Ambient temperature

-40

-20

100

Ambient temperature Ta[°C]

duty cycle [%]

DT terminal voltage

1.05V

fosc=190kHz

fosc=1MHz

FA7703/04:OUT1 Pch drive (SEL1=GND)
FA7703:OUT2

CS terminal voltage vs.Ambient temperature

1.21

1.23

1.25

1.27

1.29

1.31

1.33

-40

-20

100

Ambient temperature Ta[°C]

CS terminal voltage [V

]

FB1,FB2<1.35V

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FA7703/04

OUT terminal High side voltage vs.

Source current

100

150

200

250

300

350

400

450

OUT terminal voltage [V]

OUT terminal source urrent [mA

]

OUT1/2

Vcc=20V

Vcc=2.5V

Vcc=4.5V

Vcc=6.0V

Error Amplifier gain and Phase vs.frequency

-20

-10

Frequency [Hz]

GAIN [dB]

-20

100

120

140

160

180

PHASE [deg]

GAIN

PHASE

10k

100k

10M

OUT terminal Low side voltage vs.Sink current

100

120

140

160

180

200

0.0

0.5

1.0

1.5

2.0

2.5

OUT terminal voltage [V]

OUT terminal sink current [mA

]

OUT1/2

CS terminal source current vs.Ambient temperature

-2.40

-2.35

-2.30

-2.25

-2.20

-2.15

-2.10

-2.05

-2.00

-40

-20

100

Ambient temperature Ta[°C]

CS terminal source current [

390

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FA7703/04

8. Description of each circuit
(1)Reference Voltage Circuit

The reference voltage circuit of FA7703/04

generates the reference voltage (VREF) of
1.00V±1% compensated in temperature from
VCC voltage, and the regulated voltage (VREG)
of 2.2V ±2% for internal controlling. These
voltages start to output when the undervoltage
lockout protection (UVLO) is cancelled, and
they stabilize after the supply voltage (VCC)
reaches up to approx. 2.4V or higher. The
reference voltage (VREF) is connected to the
non-inverting input of Error Amplifier 1 and
serves as the reference voltage of Error
Amplifier 1. Because of Error Amplifiers have
offset voltage then, the precision of voltage in
practical use is 1.00V±2%. The voltage (VREF)
outputs externally from REF terminal, therefore,
it can serve as a stabilized power source. When
using it, be sure to set the output current 1mA
or below.

The regulated voltage (VREG) for internal

controlling serves as the stabilized power
source for maximum output duty setting or the
like. Be sure to set the output current 2mA or
below in operation in this case. This voltage
also serves as the control power source of all
the internal circuits of FA7703/04. A capacitor
for stabilization (CREG) is needed to be
connected to the VREG terminal. See
recommended operating conditions to
determine capacitance.

(2)Oscillator

The oscillator of FA7703/04 generates

triangular waveforms by charging and
discharging the built-in capacitor. Any desired
oscillation frequency can be obtained by setting
the value of the resistor connected to RT
terminal (Fig. 1).

The voltage oscillates between approximately

0.65V and 1.10V in charging and discharging
with almost the same gradients (Fig. 2). Your
desired oscillation frequency can be determined
by changing the gradient using the resistor (RT)
connected to RT terminal. (Large RT: Low
frequency, small RT: High frequency) The
waveforms of oscillator cannot be observed from
the outside because a terminal for this purpose
is not provided.

Approximately DC 1V is output to RT terminal.

The oscillator output is connected to PWM

comparator.

(3)Error Amplifier Circuit

Error Amplifier 1 of FA7703/04 has the inverting

input IN1(-) terminal (Pin13). The non-Inverting
input is internally connected to the reference
voltage (VB) of 1.00V±2% at 25°C. Because
error Amplifier 2 of FA7703/04 has the inverting
input IN2(-) terminal (Pin5) and non-inverted
input IN2(+) terminal (Pin4) outputting externally,
various circuit can be designed by kinds of
external circuit structures. FB terminals (Pin6,
Pin12) are the outputs of Error Amplifiers.
Voltage Gain and phase compensation can be
set by connecting a capacitor (C) and a resistor
(R) between FB terminal and IN(-) terminal.(Fig.
3) For more information about the connection for
each output voltage of power supply, refer to
Design Advice.

Fig.2

value: large

value: small

0.65V

1.10V

Fig.3

Com p

(1.0V)

Er.Am p.1

Er.Am p.2

IN1-

REF

FB1

FB2

IN2-

IN2+

Vout1

Vout2

NF2

OSC

Fig.1

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FA7703/04

(4)PWM comparator

PWM comparator of FA7703/04 has 4 input

terminals. (Fig. 4) The oscillator output

compared with the CS terminal voltage

, the

DT terminal voltage

, and the Error Amplifier

output

. Among those 3 inputs of

, and

, the one with the lowest voltage is chosen and

given priority. While the value of the chosen
voltage is lower than the value of the waveform
of oscillator output, PWM comparator output is
set to LOW. Similarly, while the value of the
chosen voltage is higher than the waveform of
oscillator output, PWM comparator output is set
to HIGH. (Fig. 5)

When FA7703/04 are turning ON, the soft start

function starts according to the CS terminal
voltage

, then the output pulses begin to widen

gradually. The maximum pulse width is adjusted
by changing the DT terminal voltage. In steady
operation, the pulse width is determined with the
condition of the Error Amplifier output

, and

then the output voltage of DC-DC converter is
stabilized. The operation flow chart of PWM
comparator and OUT terminal is shown in Fig. 5.
The output polarity of OUT1 terminal changes
according to the condition of SEL1 terminal. The
polarity of OUT 2 terminal is different between
FA7703 and FA7704; accordingly, select the type
for your desired circuit design.

(5)Soft start function

As described in Fig. 6, a capacitor C

connected to CS terminal. When the power
supply of FA7703/04 starts and the undervoltage
lockout protection circuit (UVLO) is cancelled,
the capacitor C

is charged by the internal

current source (2.2

A. typ.), and the voltage of

CS terminal rises gradually. Since the voltage of
CS terminal is connected to PWM comparator,
the output pulses begin to widen gradually, and
then the soft start function starts as a result. (Fig.
5)

(6)Timer latch short-circuit protection circuit

The short-circuit protection circuit of FA7703/04

consists of two comparators. (S.C. DET
comparator, S.C.P comparator) In steady
operation, the output of Error Amplifier is
approximately 1V, accordingly, the output of
S.C.DET comparator is set to High, and the
voltage of CS terminal is clamped at 1.27V. If the
output voltage drops due to a short-circuit or the
like, the output voltage of Error Amplifiers rises.
When the output voltage of Error Amplifiers
exceeds 1.5V(typ.), the output of S.C.DET
comparator is set to Low, and the clamp action
at the CS terminal voltage of 1.27V is cancelled,
then the voltage of CS terminal rises up to the
VREG voltage. When the voltage of CS terminal
exceeds 2.0V(typ.), the output of S.C.P
comparator is set to High, accordingly, the
output of FA7703/04 is shut off. In this case,
FA7703/04 operate in OFF latch mode and the
current consumption in this mode is 1.3mA(typ.).
The operating waveform of the voltage of CS
terminal is shown in Fig. 7.

The approximate time (tp) between the

occurrence of a short-circuit in the output and
the triggering of the short-circuit protection

Oscillation voltage

CS term inal voltage

DT term inal voltage
Error Am plifier output

PW M output

Fig.4

1.5V

2.0V

1.27V

S .C .D E T

S .C .P

U V LO

output off

2.2

C S

V C C

Fig.6

Fig.5

PW M
output

O UT1

Nch driv en

(SEL1:REG )

O UT1

Pch driv en

(SEL1:G ND)

O UT2

FA7703

O UT2

FA7704

Oscillation voltage

CS term inal voltage

DT term inal voltage

Error Am plifier output

Quality is our message

FA7703/04

function can be calculated with

0.7

tp[s]

where, C

: Capacitance of CS terminal [

: Output source current of CS terminal [

(2.

2µ

, typ.)

You can reset the timer latch action for the

short-circuit protection function by changing the
voltage of either VCC terminal or CS terminal to
the following values.

VCC terminal: below UVLO voltage (1.85V typ.)
CS terminal: below 1.83V(typ.)

(7)Output circuit

FA7703/04 contain a push-pull output stage

and can directly drive MOSFETs. The peak
current of OUT terminal is the maximum sink
current of +150mA, and the source current of
-400mA. FA7703/04 can also drive both NPN
and PNP type transistors. And in such cases,
the maximum continuous current is ±50mA.
When designing the value of output current, be
sure to consider the allowable loss accordingly.
(See Design advice)

Ch1 of FA7703/04 is available for driving both

types of MOSFETs and you can determine the
type of MOSFET, which is connected externally
by selecting the connection of SEL1 terminal
(Pin11). If SEL terminal is connected to GND
terminal, FA7703/04 can drive a Pch MOSFET. If
SEL terminal is connected to REG terminal, they
can drive Nch MOSFET.

You can accordingly design a buck converter

circuit by Pch MOSFET driving, and a boost
circuit or a fly-back converter circuit by Nch
MOSFET driving.

DO NOT leave SEL1 terminal open in operation,

and be sure to connect it to either GND terminal
or REG terminal.

(8)Power good signal/Undervoltage lockout
protection circuit (UVLO)

To protect FA7703/04 from malfunction when

the supply voltage drops, there is built-in
undervoltage lockout as a protection circuit.
When the supply voltage rises from 0V, the
UVLO circuit is canceled at VCC of 2.0V(typ.).
When the supply voltage drops, the UVLO circuit
shuts off the output at VCC of 1.85V(typ.). In this
case, CS terminal is reset to Low level.

Power good signal circuit monitors the voltage

of REG terminal, and it stops the output of
FA7703/04 until the voltage of REG terminal
exceeds approximately 1.9V in order to protect
the ICs from malfunction.

Fig.7

0.5

1.5

1.0

2.0

Start-up

soft start

momentary short circuit

short circuit

protection

Time

CS terminal voltage [V]

1.27V

2.2V

Quality is our message

FA7703/04

9. Design advice
(1)Setting oscillation frequency

As described in "(2) Oscillator" of "Description

of each circuit", any desired oscillation frequency
can be obtained by setting the value of the
resistor connected to RT terminal. (Fig. 1) The
desired oscillation frequency should be set
between 50kHz and 1MHz. The oscillation
frequency to RT can be obtained from the chart
of "Oscillation frequency vs. timing resistor"
characteristic curves or by calculating with the
formulas below.

-0.907

fosc

where, fosc: Oscillation frequency [kHz]

: Timing resistor [k

]

These formulas can only be used for rough

calculation; accordingly, be careful when
designing, because the value obtained is not
guaranteed. The operation frequency varies due
to the conditions of the tolerance of IC influence
for noises, or external discrete components etc.
When determining the values, be sure to verify
the effectiveness of the values you calculated in
an actual circuit operation.

Because it is easily affected by noises by the

high impedance, the resistor R

should be

connected as shortly as possible near RT
terminal and GND terminal,

(2)Operation around the maximum or the

minimum output duty cycle

As described in the charts of "FB terminal

voltage vs. output duty cycle", "DT terminal
voltage vs. output duty cycle", "CS terminal
voltage vs. output duty cycle" characteristic
curves, the output duty of FA7703/04 changes
sharply around the minimum and the maximum
output duty. This phenomenon occurs more
conspicuously when operating in a high
frequency (i.e. when the pulse width is narrow).
Cautious care must be taken when using high
frequency.

(3)Determining soft start period

The time from the start of charging CS terminal

to n% output duty cycle can be roughly
calculated by the following expression.

CSn

]

[

where, V

CSn

: CS terminal voltage in the output

duty of n% [V]

: Capacitance of capacitor of CS terminal

[

: Output source current of CS terminal [

2.2

(typ.)

CSn

represents the voltage of CS terminal in

the output duty of n%, and it changes according
to the operation frequency. The value is obtained
simply from the chart of "CS terminal voltage vs.
output duty cycle" characteristic curves.

Since the output source current of CS terminal

is 2.2

, which it is rather small, if the capacitor

has leak current, then the period of soft start (ts)
is easily affected. Therefore, cautious care must
be taken when determining the value.

Charging of CS terminal begins after UVLO is

cancelled. Note that the time from power-on of
Power supply to start of charging Ccs is t0 which
is not zero as described in Fig. 8. be careful.

To reset the soft start function, the voltage of

CS terminal is discharged with FA7703/04's
internal switch triggered by lowering the voltage
of Power supply below the voltage of UVLO
(1.85V, typ.). If Power supply restarts before the
voltage is sufficiently discharged, the soft start
function might not properly operate. accordingly,
cautious care must be taken about it.

Vcc

CS terminal voltage

CSn

Threshold

voltage

Fig.8

t0 : Time from power-on of VCC to reaching

unlock voltage of UVLO

Quality is our message

FA7703/04

(4)Setting the maximum output duty

If you need to control the maximum output duty

in the DC-DC converter circuit, you can control
pulse width by connecting REG terminal to DT
terminal divided with resistors R5 and R6, as
described in Fig. 9. The output duty of the
voltage of DT terminal in this case changes
according to the operation frequency, as
described in the chart of "DT terminal voltage vs.
output duty cycle" characteristic curves. Set the
output duty accordingly based on your required
operation frequency. If the maximum output duty
setting is not needed, be sure to connect DT
terminal directly to REG terminal. In this case,
the pulse width widens up to the output duty of
100%.

The voltage of DT terminal should be set in the

range of 0.65V to 1.1V(typ.). There is a
possibility of distortion of the output pulses if
strong noises or the like are applied to DT
terminal. When conducting pattern wiring, do it
as close to each terminal of the IC as possible.
Besides, it is strongly recommended to connect
a capacitor C

for a filter of noise prevention.

(5)Pull-up/Pull-down resistor at the output

section

The power source of FA7703/04 to control the

output section is supplied from the voltage of
VREG, the voltage of this power source is
accordingly not stationary below the UVLO
voltage. On the other hand, OUT terminal
becomes unsteady condition while Power supply
voltage is below UVLO voltage. Be sure to
connect a pull-up resistor/pull-down resistor
according to Fig. 10. (See Fig. 10)

(6)Restriction of external discrete

components/Recommended operating
conditions

To achieve a stable operation of FA7703/04, the

values of external discrete components
connected to VCC, REF, and CS terminals of
this IC should be within the range of
recommended operating conditions. And also
the voltage and the current applied to each
terminal should be within the recommended
operating conditions.

A Pch MOSFET is installed between VCC

terminal and OUT1 terminal, and between VCC
terminal and OUT2 terminal. Since the Pch
MOSFET has a parasitic diode, if the voltage of
OUT1 and OUT2 terminals becomes higher than
the VCC terminal voltage, the current flows from
each terminal to VCC terminal. Cautious care
must be taken accordingly when designing.

Vcc

GND

OUT1

Vcc

GND

OUT2

Fig.10

Fig.9

3 15

REG

DT1 or DT2

GND

3 15

REG

DT1 or DT2

GND

setting
m axim um

Duty cycle

Not needed

m axim um Duty
cycle

Quality is our message

FA7703/04

(7)Loss Calculation

Since it is difficult to measure IC loss directly,

the calculation to obtain the approximate loss of
the IC connected directly to a MOSFET is
described below.

When the supply voltage is VCC, the current

consumption of the IC is I

CC1

, the total input

gate charge of the driven MOSFET is Qg and
the switching frequency is fsw, the total loss Pd
of the IC can be calculated by:

VCC

CC1

+Qg

fsw).

The value in this expression is influenced by

the effects of the dependency of supply voltage,
the characteristics of temperature, or the
tolerance of parameter. Therefore, evaluate the
appropriateness of IC loss sufficiently
considering the range of values of above
parameters under all conditions.

Example)

CC1

=1.8mA for VCC=6.0V in the case of a

typical IC from the characteristics curve.
Qg=6nC, fsw=190kHz, the IC loss "Pd" is as
follows.

6.0

(1.6mA+6nC

190kHz)

17.6mW

if two MOSFETs are driven under the same

condition for 2 channels, Pd is as follows:

6.0

{1.8mA+2

(6nC

190kHz)}=24.5mW

(8)Performance of output stage

The performance of the output stage of

FA7703/04 is the maximum sink current of
150mA and the maximum source current of
400mA. The switching element externally
attached to FA7703/04 might affect switching
speed of the ICs. Cautious care must be taken
about it especially in high frequency operation. If
the performance of the ICs is not sufficient for
your design, consider adding a buffer circuit to
improve the performance.

(9)In the case of bipolar driving

If using a bipolar transistor as the switching

element, there is a possibility of the damage
from burnout due to excessive current flow
because the ICs doesn't contain an internal
limiter resistance. Therefore, be sure to install a
base resistor. (Fig. 11) In the case of driving a
bipolar transistor, control the output current of
OUT terminal within 50mA(continuous) in
operation. If you want to speed up the switching

speed, it is quite effective to install a capacitor
C

in addition.

(10)ON/OFF control

FA7703/04 can be turned ON/OFF at CS

terminal by external signal. The way to conduct
ON/OFF control is also shown in Fig. 12. When
the voltage of CS terminal is below the threshold
voltage, the duty becomes 0% and the output
turns OFF. The current consumption in this case
is 1.3mA(typ.). To switch the ICs ON, just turning
CS terminal open, then the soft start function
restarts, and the output turns back ON. ON/OFF
control at CS terminal is used for both channel,
and the control of each channel is not allowed.

10 8

Vcc

GND

OUT1
2

power supply

Fig.11

PW M.Com p

O scillation
output

CS term inal
voltage

DT term inal
voltage

Error Am plifier
output

output

DT term inal
voltage

Error Am plifier
output

output

O N/O FF

Fig.12

Quality is our message

FA7703/04

(11)Setting of the output voltage of DC-DC

converter

Figure 13 shows the ways to set each channel

of the output voltage of DC-DC converter. The
precision of output voltage based on
FA7703/04's characteristics depends on the
variation of the voltage of VB (±2%) and VREF
(±1%), and also on offset voltage, and
temperature characteristics.

selection Guide

Ch1 Buck, Boost, Fly-back

FA7703

Ch2 Buck, Inverting (Pch driven)
Ch1 Buck, Boost, Fly-back

FA7704

Ch2 Boost, Fly-back (Nch driven)

If using FA7703/04, and building:

In the case of a boost, a buck, or a fly-back circuit

in ch1, the output voltage can be calculated with:

Vout

If using FA7703, and building:

A buck circuit in ch2, the output voltage can be

calculated with:

REF

Vout

A inverting circuit in ch2, the output voltage can

be calculated

with the following formula. (the output voltage is

negative.)

REF

Vout

,where

REF

The ratio of resistance can be calculated with:

Vout

REF

(Use the absolute value of Vout2 voltage)
If setting R7=R8, then,

Vout

REF

If using FA7704, and building:

A boost, or fly-back circuit in ch2, the output

voltage can be calculated with:

REF

Vout

V out1

R 1

R 2

(1.0V)

IN1-

FB1

OUT1

SEL1

C h1:B uck(FA 7703/04)

V out1

R 1

R 2

(1.0V)

IN1-

FB1

OUT1

SEL1

REG

C h1:B oost(F A 7703/04)

V out2

R 3

R 4

IN2-

FB2

OUT2

IN2+

REF

C h2:B uck(FA 7703)

Vout2

IN2-

FB2

OUT2

IN2+

REF

Ch2:Inverting(FA7703)

V out2

R 3

R 4

IN2-

FB2

OUT2

IN2+

REF

C h2:B oost(FA 7704)

Please note that DO NOT leave SEL1 terminal

open in operation, and be sure to connect it to
GND or VREG terminal.

Fig.13

Quality is our message

FA7703/04

(12)To protect FA7703/04 from application of

negative voltage

If rather large negative voltage is applied to any

terminal of FA7703/04, then internal parasitic
elements start operating, and they may cause
malfunctions. Accordingly, the negative voltage,
which is applied to each terminal of the ICs,
must be kept above -0.3V.

In the case of OUT terminal, in particular, the

oscillation of voltage occurring after MOSFET's
turning off can be applied to OUT terminal
through MOSFET's parasitic capacitance. As a
result, there is a possibility that the negative
voltage is applied to OUT terminal. If this
negative voltage reaches -0.3V or below,
connect an Schottky barrier diode between OUT
terminal and GND terminal as shown in Fig. 14.
The Schottky barrier diode's forward direction
voltage clamps the voltage applied to OUT
terminal. In this case, use the Schottky barrier
diode with low voltage drop in forward direction.
Other terminals should be kept above -0.3 V
also based on the same reasons.

(13)Forbidden use of external forcible

latched operation for CS terminal

If the external voltage of 2.0V or more is

forcibly applied to CS terminal in normal
operation (clamped at 1.2V), the IC may be
seriously damaged because the clamp circuit is
not equipped with any resistor for limiter.
Therefore, DO NOT apply external high voltage
to CS terminal.

10 8

Vcc

GND

OUT1
2

SBD

Fig.14

Quality is our message

FA7703/04

10.Application circuit

FA7703

DT 2

IN2+

IN2-

FB2

G ND

O UT 2

REG

DT 1

REF

IN1-

FB1

SEL1

O UT 1

VCC

Vin

2.5 to 8.0V

10V/100mA

-7.5V/100mA

11k

10k

2200pF

0.1

11k

10k

16k

10k

22k

4700pF

Vin

8 to 18V

5V/500mA

30V/20mA

FA7704

DT 2

IN2+

IN2-

FB2

G ND

O UT 2

REG

DT 1

REF

IN1-

FB1

SEL1

O UT 1

VCC

10k

4700pF

0.1

10k

11k

10k

1.5k

0.1

43k

10k

4700pF

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