FA7703/04
FA7703/7704
FUJI Power Supply Control IC
DC/DC Power Supply control IC
FA7703/7704
Application Note
June-2010
Fuji Electric Systems Co.,Ltd.
Fuji Electric Systems Co., Ltd.
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FA7703/04
FA7703/7704
WARNING
1. This Data Book contains the product specifications, characteristics, data, materials, and structures as
of June 2010. 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
7. Copyright © 1995 by Fuji Electric Co., Ltd. All rights reserved. No part of this Data Book may be
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.
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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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FA7703/7704
1. 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.
2. Features
z Wide range of supply voltage
FA7703 : VCC=2.5 to 30V FA7704 : VCC=2.5 to 20V
z Direct driving of MOSFET
z Switching Pch/Nch driving is available (channel 1 only)
z Low current consumption is achieved by CMOS process:
1.8mA (typ.) in operation
z 2ch PWM control IC
z High frequency operation is available: 50kHz to 1MHz
z Simple setting of operation frequency with a timing resistor
z Soft start setting is available
z Setting of the limitation of maximum output duty cycle is available in each channel
z Built-in protection function for undervoltage lockout
z Highly accurate reference voltage:
VREF: 1.00V±1%, VB: 1.00V±2%, VREG: 2.20V±2%
z Built-in output timer latched short-circuit protection circuit
z Thin and small package: TSSOP-16, SOP-16
3. Outline
TSSOP-16 (V)
SOP-16 (M)
0 . 71 ± 0 . 1
7.8 ± 0.2
6 .4 ± 0.1
4 . 40 ± 0. 05
5.3 ± 0.3
5.0 ±0.1
1.10MAX
1.9 ± 0.2
10.2 ±0.3
1.27
0.4 ±0.05
0.65
units:mm
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4. Block diagram
REG
DT1
REF
IN1-
FB1
SEL1
OUT1
VCC
16
15
14
13
12
11
10
9
7
8
Er.Am p1
+
+
+
Reference
voltage
1V
2.2V
I CS
PW M.Com p1
O N/O FF
S.C.P
1.3V
BIAS
UVLO
Power G ood Signal
1.5V
+
-
2.0V
S.C.DET
BIAS
+
+
+ PW M.Com p2
Er.Am p2
O N/OFF
FA7704
OSC
1
2
3
4
RT
CS
DT2
IN2+
5
IN2-
6
FB2
GND
OUT2
5. Selection Gide
FA7703
FA7704
6. Pin assignment
Pin
Pin No
symbol
1
RT
2
CS
3
DT2
4
IN2+
5
IN26
FB2
7
GND
8
OUT2
9
VCC
10
OUT1
11
SEL
12
FB1
13
IN114
REF
15
DT1
16
REG
Ch.1(OUT1)
Ch.2(OUT2)
Ch.1(OUT1)
Ch.2(OUT2)
Buck, Boost, Fly-back
Buck, Inverting (Pch driven)
Buck, Boost, Fly-back
Boost, Fly-back (Nch driven)
Description
Oscillator timing resistor
Soft start, Timer latched short circuit protection, ON/OFF control
Ch.2 Dead Time Adjustment
Ch.2 non-inverting input to error amplifier
Ch.2 inverting input to error amplifier
Ch.2 output o error amplifier
Ground
Ch.2 output
Power supply
Ch.1 output
Selection of type of driven MOSFET (OUT1)
Ch.1 output o error amplifier
Ch.1 inverting input to error amplifier
Reference voltage
Ch.1 Dead Time Adjustment
Regulated voltage output
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7. 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
FA7703
30
VCC
V
FA7704
20
REF Terminal output current
IREF
1
mA
REG Terminal output current
IREG
2
mA
OUT1, OUT2 Terminal source current ISOpeak
-400(peak)
mA
-50(continuos)
mA
ISOcont
OUT1, OUT2 Terminal sink current
ISIpeak
+150(peak)
mA
+50(continuos)
mA
ISIcont
RT,CS,REG,REF,IN1-,IN2+,IN2-,FB1,
+2.5(max.)
VLOGIC
V
FB2,DT1,DT2,SEL1 Terminal voltage
-0.3(min.)
Power dissipation
TSSOP
300
Pd
mW
SOP
400
(Ta≤25°C)*
Operating ambient temperature
Ta
-30 to +85
°C
Operating junction temperature
Tj
+125
°C
Storage temperature
Tstg
-40 to +150
°C
*:Maximum dissipation curve at Ta≥25°C is shown under figure.
Maximum power dissipation Pd[mW]
Maximum power dissipation curve
500
SOP
400
300
TSSO
200
100
0
-30
0
30
60
90
120
150
Ambient temperature Ta[°C]
(2)Recommended operating conditions
Item
Symbol
MIN.
TYP.
MAX.
Units
Supply voltage
FA7703
2.5
6
28
Vcc
V
FA7704
2.5
6
18
DC feedback resistor of
100
RNF
kΩ
error amplifier
VCC terminal capacitance*
CVCC
0.1
μF
REG terminal capacitance
CREG
0.047
0.1
1
μF
CS terminal capacitance
CCS
0.01
10
μF
Oscillation frequency
fOSC
50
1000
kHz
SEL1 terminal Pch,PNP driving
VSEL1L
Connect to GND
voltage
Connect to REG terminal
Nch,NPN driving
VSEL1H
*Please select the proper value by input-output conditions of power supply.
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(3)Electrical characteristics [Unless otherwise standard,Ta=25°C,Vcc=6V,RT=22kΩ]
(1) Internal Bias Section (REF terminal voltage)
Item
Symbol
Conditions
MIN.
TYP.
MAX.
Output Voltage
REF terminal load current
0.990
1.000
1.010
VREF
IREF=0mA
Line Regulation
FA7703:Vcc=2.5 to 28V,IREF=0mA
±1
±5
VLINEF
FA7704:Vcc=2.5 to 18V,IREF=0mA
Load Regulation
VLDF
IREF=0 to 1mA
-10
-3
Variation
Ta=-30 to +85°C
-0.8 to
VTCF
with temperature
Change rate for value at 25°C
+0.2
(2) Regulated Voltage for Internal Control Blocks Section (REG terminal voltage)
Item
Symbol
Conditions
MIN.
TYP.
Output Voltage
REG terminal load current
2.156
2.200
VREG
IREG=0mA
Line Regulation
FA7703:Vcc=2.5 to 28V,IREG=0mA
±4
VLINEG
FA7704:Vcc=2.5 to 18V,IREG=0mA
Load Regulation
VLDG
IREG=0 to 2mA
-12
-2
Variation
Ta=-30 to +85°C
-0.8 to
VTCG
with temperature
Change rate for value at 25°C
+0.2
(3) Oscillator Section
Item
Oscillation frequency
Line Regulation
Variation
With temperature
Symbol
fOSC
f
LINE
fTC1
fTC2
Conditions
RT=22kΩ
FA7703:Vcc=2.5 to 28V
FA7704:Vcc=2.5 to 18V
Ta=+25 to -30°C, f=50k to 1MHz
Ta=+25 to +85°C, f=50k to1MHz
MIN.
160
TYP.
190
±0.1
mV
mV
%
MAX.
2.244
Units
V
±14
mV
mV
%
MAX.
220
±2
±3
(4) Error Amplifier Section (Input:IN1-,IN2+,IN2-,Output:FB1,FB2 terminal)
Item
Symbol
Conditions
MIN.
Reference Voltage
VB
IN1- terminal threshold voltage
0.980
(ch1)
Input offset (ch2)
VOFST
(IN2+) - (IN2-)
Common mode input
0.3
VIN
voltage
Input Current
IIN
-100
Open Loop Gain
AVO
70
Unity Gain Bandwidth
fT
Output Source Current
FB1,2
-220
IOHE
terminal voltage=VREF-0.5V
Output sink Current
IOLE
FB1,2 terminal voltage=0.5V
3
Units
V
Units
kHz
%
%
%
TYP.
1.000
MAX.
1.020
Units
V
-
±10
1.4
mV
V
0
+100
1.5
-160
-100
nA
dB
MHz
μA
6
12
mA
(5) Pulse Width Modulation Section (FB1,FB2 terminal)
Item
Symbol
Conditions
Input threshold voltage
VFB0
Duty Cycle=0%
Input threshold voltage
VFB100 Duty Cycle=100%
MIN.
0.550
1.000
TYP.
0.650
1.100
MAX.
0.750
1.200
Units
V
V
(6) Dead Time Adjustment Circuit Section (DT1, DT2 terminal)
Item
Symbol
Conditions
Input threshold voltage
VDT0
Duty Cycle=0%
Input threshold voltage
VDT100 Duty Cycle=100%
MIN.
0.550
1.000
TYP.
0.650
1.100
MAX.
0.750
1.200
Units
V
V
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(7) Under Voltage Lock-Out Section (VCC terminal)
Item
Symbol
Conditions
ON threshold
VCCON
OFF threshold
VCCOF
Hysteresis Voltage
VCCHY
Variation
Ta=-30 to +25°C
VCCHY
with temperature
Ta=+25to +85°C
(8) Soft Start Section (CS terminal)
Item
Symbol
Conditions
CS=0V
Output source current
ICS
Threshold Voltage1
VCS0
Duty Cycle=0%
Threshold Voltage2
VCS50
Duty Cycle=50%
(9) Short circuit Protection Section (FB terminal, CS terminal)
Item
Symbol
Conditions
Short Detection
FB terminal voltage
VFBTH
Threshold Voltage
Latched Mode
CS terminal voltage
VCSTH
Threshold Voltage
Latched Mode
CS terminal voltage
VCSRE
Reset Voltage
Latched Mode
CS terminal voltage
VCSHY
Hysteresis
CS terminal
VCSCL1 FB terminal voltage<1.35V
Clamped Voltage
VCSCL2 FB terminal voltage>1.65V
(10) Output Stage Section (OUT1,OUT2 terminal,SEL1 terminal)
Item
Symbol
Conditions
High side on resistance
RONH
VCC=6V,Source Current=-50mA
High side on resistance
RONH
VCC=2.5V,Source Current=-50mA
Low side on resistance
RONL
VCC=6V,Sink Current=+50mA
Low side on resistance
RONL
VCC=2.5V,Sink Current=+50mA
Rise Time
trn
330pF Load to GND terminal
trp
330pF Load to VCC terminal
Fall Time
tfn
330pF Load to GND terminal
tfp
330pF Load to VCC terminal
SEL1 terminal Input
Pch-MOSFET,
VSEL1L
Voltage
PNP transistor driving
Nch-MOSFET,
VSEL1H
NPN transistor driving
(11) Overall Section (VCC terminal)
Item
Symbol
Conditions
Operating mode
Duty Cycle=0%,OUT1/2:open
Supply Current
ICC0
CS=0V, FB1,FB2≈VREG
RT=22kΩ,f≈190kHz
Duty Cycle=80%,OUT1/2:open
ICC1
RT=22kΩ,f≈190kHz
Duty Cycle=80%,OUT1/2:open
ICC2
RT=3kΩ,f≈1MHz
Latched mode
CS>2.1V,FB1,FB2≈VREG,
ICCLAT
Supply Current
RT=22kΩ,f≈190kHz
MIN.
TYP.
2.00
1.85
0.15
+0.3
-0.1
MAX.
2.25
MIN.
-2.8
0.550
TYP.
-2.2
0.650
0.880
MAX.
-1.6
0.750
Units
μA
V
V
MIN.
1.350
TYP.
1.500
MAX.
1.650
Units
V
1.900
2.000
2.100
V
1.40
0.05
0.35
Units
V
V
V
mV/°C
mV/°C
1.830
V
30
170
300
mV
1.200
2.120
1.270
2.200
1.340
2.280
V
V
MIN.
TYP.
10
18
5
5
20
20
35
35
MAX.
20
36
10
10
0
0.2
Units
Ω
Ω
Ω
Ω
ns
ns
ns
ns
V
VREG-
VREG
V
TYP.
1.3
MAX.
1.9
Units
mA
1.8
2.7
mA
3.1
4.7
mA
1.3
1.9
mA
0.2
MIN.
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Characteristics curves
Timing resistor vs.Oscillation frequency
Oscillation frequency vs.ambient temperature
Vcc=6V
1000
Vcc=6V,RT=22k Ω
195
Oscillation frequency [kHz]
Oscillation frequency [kHz]
194
100
193
192
191
190
189
188
187
186
10
185
1
10
Timing resistor RT[k Ω]
100
-40
0
20
40
60
Ambient temperature Ta[°C]
80
100
Regulated voltage vs.Ambient temperature
Regulated voltage vs.Supply voltage VCC
IREG=0A,RT=22k Ω
2.22
-20
IREG=0A,RT=22k Ω
2.24
Regulated voltage VREG[V]
Regulated voltage VREG[V]
2.23
2.21
2.20
2.19
2.22
2.21
2.20
2.19
2.18
2.17
2.18
2.16
0
5
10
Supply voltage Vcc[V]
15
20
-40
Reference voltage vs.Supply voltage VCC
80
100
IREF=0A,RT=22k Ω
1.02
Reference voltage VREF[V]
Reference voltage VREF[V]
0
20
40
60
Ambient temperature Ta[°C]
Reference voltage vs.Ambient temperature
IREF=0A,RT=22k Ω
1.010
-20
1.005
1.000
0.995
0.990
1.01
1.00
0.99
0.98
0
5
10
Supply voltage Vcc[V]
15
20
-40
-20
0
20
40
60
Ambient temperature Ta[°C]
80
100
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FA7703/7704
FB terminal voltage vs.Duty cycle
FB terminal voltage vs.Duty cycle
FA7703/04:OUT1 Nch driven (SEL1=REG)
FA7704:OUT2
FA7703/04:OUT1 Pch driven (SEL1=GND)
FA7703:OUT2
100
90
90
80
80
fosc=1MHz
70
Duty cycle [%]
Duty cycle [%]
70
60
50
40
30
20
50
40
30
20
fosc=190kHz
10
fosc=1MHz
60
fosc=190kHz
10
0
0
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
0.5
0.6
0.7
FB terminal voltage [V]
1.1
1.2
90
80
80
fosc=1MHz
70
70
Duty cycle [%]
Duty cycle [%]
1.0
FA7703/04:OUT1 Pch driven (SEL1=GND)
FA7703:OUT2
100
90
60
50
40
30
20
fosc=1MHz
60
50
40
30
20
fosc=190kHz
10
fosc=190kHz
10
0
0
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
0.5
0.6
0.7
DT terminal voltage [V]
100
0.8
0.9
1.0
DT terminal voltage [V]
CS terminal voltage vs.Duty cycle
CS terminal voltage vs.Duty cycle
FA7703/04:OUT1 Nch driven (SEL1=REG)
FA7704:OUT2
FA7703/04:OUT1 Pch drivenb (SEL1=GND)
FA7703:OUT2
100
90
1.1
1.2
90
80
80
fosc=1MHz
70
70
Duty cycle [%]
Duty cycle [%]
0.9
DT terminal voltage vs.Duty cycle
DT terminal voltage vs.Duty cycle
FA7703/04:OUT1 Nch driven (SEL1=REG)
FA7704:OUT2
100
0.8
FB terminal voltage [V]
60
50
40
30
20
50
40
30
20
fosc=190kHz
10
fosc=1MHz
60
fosc=190kHz
10
0
0
0.5
0.6
0.7
0.8
0.9
1.0
CS terminal voltage [V]
1.1
1.2
0.5
0.6
0.7
0.8
0.9
1.0
CS terminal voltage [V]
1.1
1.2
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Duty cycle vs. Ambient temperature
Duty cycle vs. Ambient temperature
FA7703/04:OUT1 Nch drive (SEL1=REG)
FA7704:OUT2
94
DT terminal voltage≈1.05V
DT terminal voltage≈1.05V
92
92
90
90
fosc=190kHz
duty cycle [%]
duty cycle [%]
FA7703/04:OUT1 Pch drive (SEL1=GND)
FA7703:OUT2
94
88
86
84
fosc=1MHz
86
84
82
82
80
80
78
fosc=190kHz
88
fosc=1MHz
78
-40
-20
0
20
40
60
Ambient temperature Ta[°C]
80
100
-40
Duty=80%,
IN(-)-FB:shorted
80
100
FB1,FB2<1.35V
1.33
fosc=1MHz
1.31
2.5
CS terminal voltage [V]
Operating mode supply current [mA]
0
20
40
60
Ambient temperature Ta[°C]
CS terminal voltage vs.Ambient temperature
Operating mode supply current vs.Supply voltage
3.0
-20
2.0
fosc=190kHz
1.5
1.0
0.5
1.29
1.27
1.25
1.23
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1.21
3.5
-40
Supply voltage Vcc[V]
-20
0
20
40
60
Ambient temperature Ta[°C]
80
100
Operating supply current vs.Ambient temperature
Duty=80%
RT=22kΩ
Operating supply current [mA]
2.5
2.0
Vcc=6V
1.5
1.0
-40
-20
0
20
40
60
Ambient temperature Ta[°C]
80
100
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OUT terminal High side voltage vs.
Source current
450
OUT terminal Low side voltage vs.Sink current
OUT1/2
200
OUT1/2
180
Vcc=20V
350
OUT terminal sink current [mA]
OUT terminal source urrent [mA]
400
300
250
Vcc=6.0V
200
150
Vcc=4.5V
100
Vcc=2.5V
50
160
140
120
100
80
60
40
20
0
0
0
5
10
15
OUT terminal voltage [V]
20
25
0.0
Error Amplifier gain and Phase vs.frequency
160
100
PHASE
30
80
20
60
10
40
0
20
-10
0
-20
-20
1
10
1k
10k
100k
1M
PHASE [deg]
GAIN [dB]
120
40
2.5
-2.05
140
50
2.0
-2.00
CS terminal source current [ A]
180
70
GAIN
1.0
1.5
OUT terminal voltage [V]
CS terminal source current vs.Ambient temperature
80
60
0.5
10M
-2.10
-2.15
-2.20
-2.25
-2.30
-2.35
-2.40
-40
Frequency [Hz]
-20
0
20
40
60
Ambient temperature Ta[°C]
80
100
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FA7703/04
FA7703/7704
9. 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.
OSC
1
Fig.1
RT
RT
RT value: small
RT value: large
1.10V
0.65V
Fig.2
(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.
RFB1
CFB1
Vout1
R1
Er.Amp.1
IN1-
FB1
13
R2
12
14
REF
Vout2
IN2+
Comp
VB
(1.0V)
Er.Amp.2
Comp
FB2
4
R4
6
5
R3
IN2-
RFB2
CFB2
Fig.3
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(4)PWM comparator
PWM comparator of FA7703/04 has 4 input
terminals. (Fig. 4) The oscillator output 2 is
compared with the CS terminal voltage 1, the
DT terminal voltage 3, and the Error Amplifier
output 4. Among those 3 inputs of 1, 3, and
4, 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 1, 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 4, 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.
1
CS term inal voltage
2
Oscillation voltage
3
DT term inal voltage
4
Error Am plifier output
+
+
+
PW M output
Fig.4
4
2
Oscillation voltage
Error Am plifier output
3 DT term inal voltage
1
CS term inal voltage
PW M
output
O UT1
Nch driv en
(SEL1:REG )
O UT1
Pch driv en
(SEL1:G ND)
O UT2
FA7703
O UT2
FA7704
Fig.5
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(5)Soft start function
As described in Fig. 6, a capacitor C CS is
connected to CS terminal. When the power
supply of FA7703/04 starts and the undervoltage
lockout protection circuit (UVLO) is cancelled,
the capacitor C CS is charged by the internal
current source (2.2μA. 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)
CS
2.2 μ A
2
VCC
C CS
output off
1.27V
UVLO
S.C.P
1.5V
+
-
2.0V
S.C.DET
FB
Fig.6
(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
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FA7703/04
FA7703/7704
occurrence of a short-circuit in the output and
the triggering of the short-circuit protection
function can be calculated with
tp[s] ≈
0.7 × CCS
ICS
where, C CS: Capacitance of CS terminal [μF]
ICS: Output source current of CS terminal [μA]
(2.2μΑ, 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.)
2.2V
CS terminal voltage [V]
2.0
1.5
1.27V
1.0
tp
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.
short circuit
protection
Start-up
short circuit
momentary short circuit
0.5
soft start
0
Time
Fig.7
(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.
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10. 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.
fosc = 3 ×10 3 × RT -0.907
1.1
⎛ 3 × 10 3 ⎞
⎟⎟
RT = ⎜⎜
⎝ fosc ⎠
where, fosc: Oscillation frequency [kHz]
R T: Timing resistor [kΩ]
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 T 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.
ts[ s ] =
VCSn × CCS
ICS
where, VCSn: CS terminal voltage in the output
duty of n% [V]
C CS: Capacitance of capacitor of CS terminal
[μF]
ICS: Output source current of CS terminal [μA]
2.2μΑ (typ.)
VCSn 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 2.2μΑ, 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
Threshold
voltage
CS terminal voltage
VCSn
t0
ts
t0 : Time from power-on of VCC to reaching
unlock voltage of UVLO
Fig.8
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(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 DT for a filter of noise prevention.
16 REG
R6
3
C DT
V IN
Vcc
9
16 REG
DT1 or DT2
R5
(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.
15
OUT1
DT1 or DT2
3
10
15
GND
GND
7
7
GND
setting
m axim um
Duty cycle
Not needed
m axim um Duty
cycle
Fig.9
7
V IN
(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)
Vcc
9
OUT2
8
GND
7
Fig.10
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(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 ICC1, 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:
Pd ≈ VCC ×(ICC1+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)
ICC1=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.
Pd ≈ 6.0× (1.6mA+6nC×190kHz) ≈17.6mW
if two MOSFETs are driven under the same
condition for 2 channels, Pd is as follows:
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 B in addition.
power supply
Vcc
9
CB
OUT1
2
10
8
RB
GND
7
Fig.11
(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.
Pd ≈ 6.0×{1.8mA+2× (6nC×190kHz)}=24.5mW
Oscillation
output
(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.
DT term inal
voltage
12
ON/OFF
Error Am plifier
output
2
CS term inal
voltage
DT term inal
voltage
+
+
+
output
+
+
+
output
PW M.Com p
6
Error Am plifier
output
7
Fig.12
(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
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(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.
Ch1:Buck(FA7703/04)
Vout1
11
R1
SEL1
13
IN1-
12
+
R2
VB
(1.0V)
10
OUT1
7
Ch1:Boost(FA7703/04)
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)
Vout1
R1
13
16
11
REG
SEL1
IN1-
R2
12
+
Vout1
FB1
VB
(1.0V)
OUT1
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:
Vout1 =
Vout1
FB1
10
7
R1 + R 2
× VB
R2
Ch2:Buck(FA7703)
Vout2
If using FA7703, and building:
A buck circuit in ch2, the output voltage can be
calculated with:
R4
14
REF
5
IN2-
6
+
R3
R3 + R 4
Vout 2 =
× VREF
R3
-
Vout2
FB2
4
IN2+
OUT2
8
7
A inverting circuit in ch2, the output voltage can
be calculated
with the following formula. (the output voltage is
negative.)
Ch2:Inverting(FA7703)
R3 + R 4
R4
×V1 −
× VREF
R3
R3
R8
,where V 1 =
× VREF
R7 + R8
R7
R3
Vout 2 =
14
REF
4
IN2+
R4
V1
+
6
IN2-
8
OUT2
The ratio of resistance can be calculated with:
Vout2
FB2
5
7
R3 VREF − V 1
=
R 4 Vout 2 + V 1
Vout2
R8
Ch2:Boost(FA7704)
Vout2
(Use the absolute value of Vout2 voltage)
If setting R7=R8, then,
Vout 2 = VREF
R4
⎛ R3 − R 4 ⎞
×⎜
⎟
⎝ 2 R3 ⎠
IN2-
R3
REF
-
6
+
FB2
4
Vout2
IN2+
OUT2
If using FA7704, and building:
A boost, or fly-back circuit in ch2, the output
voltage can be calculated with:
R3 + R 4
Vout 2 =
× VREF
R3
14
5
8
7
Fig.13
Please note that DO NOT leave SEL1 terminal
open in operation, and be sure to connect it to
GND or VREG terminal.
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FA7703/04
FA7703/7704
(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.
Vcc
9
OUT1
2
10
GND
7
8
SBD
Fig.14
(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.
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FA7703/04
FA7703/7704
11. Application circuit
10V/100mA
1k Ω
Vin
2.5 to 8.0V
9k Ω
1k Ω
11k Ω
16
15
14
REG
DT 1
REF
2200pF
10k Ω
-7.5V/100mA
13
12
11
IN1-
FB1
SEL1
10
O UT 1
9
VCC
FA7703
0.1 μ F
11k Ω
RT
CS
DT 2
2
3
IN2+
IN2-
FB2
G ND
4
5
6
7
O UT 2
8
4700pF
1
10k Ω
1μ F
10k Ω
22k Ω
10k Ω
1k Ω
10k Ω
16k Ω
5V/500mA
1k Ω
Vin
8 to 18V
4k Ω
4700pF
10k Ω
16
15
14
REG
DT 1
REF
30V/20mA
13
12
11
IN1-
FB1
SEL1
10
O UT 1
9
VCC
FA7704
0.1 μ F
11k Ω
CS
2
DT 2
3
IN2+
IN2-
FB2
G ND
4
5
6
7
10k Ω
O UT 2
8
4700pF
10k Ω
RT
1
0.1 μ F
10k Ω
1.5k Ω
43k Ω
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