FA3687V
Quality is our message
FUJI Power Supply Control IC
FA3687V
Application Note
May –2001
Fuji Electric Co., Ltd.
Matsumoto Factory
1
FA3687V
Quality is our message
WARNING
1.This Data Book contains the product specifications, characteristics, data, materials, and structures as of May 2001.
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 (pin 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.
2
FA3687V
Quality is our message
CONTENTS
page
1.
Description
･･･････････････････
4
2.
Features
･･･････････････････
4
3.
Outline
･･･････････････････
4
4.
Block diagram
･･･････････････････
5
5.
Pin assignment
･･･････････････････
5
6.
Ratings and characteristics
･･･････････････････
6
7.
Characteristic curves
･･･････････････････
10
8.
Description of each circuit
･･･････････････････
17
9.
Design advice
･･･････････････････
21
Application circuit
･･･････････････････
25
10.
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.
3
FA3687V
Quality is our message
1. Description
FA3687V is a PWM type DC-to-DC converter control IC with 2ch outputs that can directly drive power MOSFETs.
CMOS devices with high breakdown voltage are used in this IC and low power consumption is achieved. This IC is
suitable for very small DC-to-DC converters because of their small and thin package (1.1mm max.), and high
frequency operation (to 1.5MHz). You can select Pch or Nch of MOSFETs driven, and design any topology of DC-toDC converter circuit like a buck, a boost, a inverting, a fly-back, or a forward.
2. Features
・
・
・
・
・
・
・
・
・
・
・
・
・
Wide range of supply voltage: VCC=2.5 to 20V
MOSFET direct driving
Selectable output stage for Pch/Nch MOSFET on each channel
Low operating current by CMOS process: 2.5mA (typ.)
2ch PWM control IC
High frequency operation: 300kHz to 1.5MHz
Simple setting of operation frequency by timing resistor
Soft start function at each channel
Adjustable maximum duty cycle at each channel
Built-in undervoltage lockout
High accuracy reference voltage: VREF: 1.00V±1%, VREG: 2.20V±1%
Adjustable built-in timer latch for short-circuit protection
Thin and small package: TSSOP-16
3. Outline
4
FA3687V
Quality is our message
4. Block diagram
⑬ ＶＲＥＧ
Reference
voltage
2.20V
⑦ CS2
⑩ CS1
ＵＶＬＯ
Soft
start
Regulated
voltage
1.00V
⑫ RT
⑥ ＶCC
Oscillator
＋
Er.Amp.1
−
⑭ IN1-
Comp.1
＋
N/P ch.
drive
−
⑨ OUT1
⑮ FB1
⑤ IN2+
＋
Er.Amp.2
−
④ IN2-
⑯ SEL1
Comp.2
−
N/P ch.
drive
＋
⑧ OUT2
③ FB2
② SEL2
FB voltage
detection
Timer
latch
① CP
5. Pin assignment
Pin
Pin
No.
symbol
1
CP
2
SEL2
Selection of type of driven MOSFET (OUT2)
3
FB2
Ch.2 output of error amplifier
4
IN2-
Ch.2 inverting input to error amplifier
5
IN2+
Ch.2 non-inverting input to error amplifier
6
VCC
Power supply
7
CS2
Soft start for Ch.2
8
OUT2
Ch.2 output
9
OUT1
Ch.1 output
10
CS1
Soft start for Ch.1
11
GND
Ground
12
RT
Oscillator timing resistor
13
VREG
Regulated voltage output
14
IN1-
Ch.1 inverting input to error amplifier
15
FB1
Ch.1 output of error amplifier
16
SEL1
Selection of type of driven MOSFET (OUT1)
Description
Timer latched short circuit protection
5
⑪ GND
FA3687V
Quality is our message
6. Ratings and characteristics
(1) Absolute maximum ratings
Item
Symbol Test condition
Power supply voltage
SEL1・SEL2 pin voltage
FB1・IN1-・FB2・IN2-・IN2+
pin voltage
CS1･CS2･CP･RT･VREG
pin voltage
OUT1/2 OUT pin source current
OUT pin sink current
OUT1/2 OUT pin source current
OUT pin sink current
※1
Power dissipation
rating
Unit
VCC
VSEL
20
V
-0.3 to 5.0
V
VEA_IN
-0.3 to 5.0
V
VCTR_IN
-0.3 to 5.0
V
IOUT-
-400(peak)
mA
IOUT+
150(peak)
mA
IOUT-
-50(continuous)
mA
IOUT+
50(continuous)
mA
Ta≦25℃
Pd
300
mW
Operating junction temperature
TJ
+125
℃
Operating ambient temperature
TOPR
-30 to +85
℃
Storage temperature
TSTG
-40 to +125
℃
※1 Derating factor Ta≧25℃ : 3mW/℃
Maximun power dissipation
[mW］
Maximum power dissipation curve
350
300
250
200
150
100
50
0
-30
0
30
60
90
120
150
Ambient temperature [℃]
(2) Recommended operating conditions
Item
MIN.
TYP.
MAX.
Unit
VCC
2.5
‐
18
V
CS1･CS2･CP pin voltage
SEL1･SEL2 pin voltage
VCTR_IN
VSEL_IN
0.0
0.0
‐
-
2.5
2.5
V
V
IN1-･IN2-･IN2+ pin voltage
VEA_IN
0.0
‐
2.5
V
Oscillation frequency
fOSC
300
500
1500
kHz
CREG
Vcc＜10V
0.1
1.0
4.7
μF
VREG pin capacitance
10V≦Vcc＜18V
0.47
1.0
4.7
μF
VREG pin current
IREG
‐
‐
1.0
mA
VCC pin capacitance
CVCC
1.0
‐
‐
μF
CS1 pin capacitance
CCS1
Between CS1 and GND
0.01
‐
‐
μF
CS2 pin capacitance
CP pin capacitance
CCS2
CCP
Between CS2 and VREG
‐
―
‐
―
μF
μＦ
Supply voltage
Symbol
Test condition
0.01
Between CP and VREG ※2 ０．０１
※2. If the timer latched mode is not needed, connect the CP pin to GND.
6
FA3687V
Quality is our message
(3) Electrical characteristics
* The characteristics is based on the condition of VCC=3.3V, CREG=1.0μF, RT=12kΩ, Ta=+25℃, unless
otherwise specified.
(1) Regulated voltage for internal control blocks (VREG pin)
Item
Regulated voltage
Symbol
Test condition
VREG
MIN.
TYP.
MAX.
Unit
2.178
2.200
2.222
V
±15
mV
Line regulation
VREG_LINE VCC=2.5 to 18V
―
±5
Load regulation
VREG_LOAD IREG=0 to 1mA
-5
-1
mV
±0.5
%
Variation with temperature
VREG_TC
Ta=-30 to +85℃
(2) Oscillator section (RT pin)
Item
Oscillation frequency
Symbol
Test condition
fOSC
Line regulation
fOSC_LINE
VCC=2.5 to 18V
Variation with temperature
fOSC_TC1
Ta=-30 to +85℃
(3)
MIN.
TYP.
MAX.
Unit
435
500
565
kHz
―
±1
±5
%
±3
%
Error Amplifier section (IN1-・FB1・IN2-・IN2+・FB2 pin)
Item
Reference voltage (ch.1)
Symbol
VREF1
Test condition
※3
VREF1 Line regulation (ch.1)
VREF_LINE
VCC=2.5 to 18V
VREF1Variation
VREF_TC1
Ta=-30 to +85℃
Input offset voltage (ch.2)
VOFFSET
VIN2+=1.0V，IN2+・IN2-
VOFFSET Line regulation (ch.2)
VOFF_LINE
VCC=2.5～18V
MIN.
TYP.
MAX.
Unit
0.99
1.00
1.01
V
―
±2
±5
mV
±0.5
%
with temperature (ch.1)
Input bias current
IIN-
―
VINx-=0.0 to 2.5V
IN2+・IN2-
―
±10
ｍＶ
0
ｍＶ
0.0
mA
Ｖ
Common mode input voltage
VCOM
Open loop gain
AVO
70
dB
Unity gain bandwidth
fT
1.5
MHz
Output current (sink)
ISIFB
0.7
VFB1=0.5V,VIN1-=VREG
1.5
2.3
3.5
4.7
mA
-360
-270
-180
μA
VFB2=0.5V,VIN2-=VREG,VIN2+=1V
Output current (source)
ISOFB
VFB1=VREG-0.5V,VIN1-=0V
VFB2=VREG-0.5V,VIN2-=0V,VIN2+=1V
* 3: The FB1 voltage is measured under the condition that IN1- pin and FB1 pin are shorted. The input offset voltage of
the error amplifier is included.
7
FA3687V
Quality is our message
(4) Soft start section (CS1・CS2 pin)
Item
Symbol
Test condition
MIN.
TYP.
MAX.
Unit
Ｖ
VCS1D0N
Duty cycle=0%, VFB1=1.4V
0.82
Threshold voltage (CS1)
VCS1D20N
Duty cycle =20%, VFB1=1.4V
0.89
0.925
0.96
Ｖ
(Driving Nch-MOSFET)
VCS1D80N
Duty cycle =80%, VFB1=1.4V
1.25
1.285
1.32
Ｖ
VCS1D100N Duty cycle =100%, VFB1=1.4V
1.38
Ｖ
0.82
Ｖ
VCS1D0P
Duty cycle =0%, VFB1=1.4V
Threshold voltage (CS1)
VCS1D20P
Duty cycle =20%, VFB1=1.4V
0.90
0.935
0.97
Ｖ
(Driving Pch-MOSFET)
VCS1D80P
Duty cycle =80%, VFB1=1.4V
1.26
1.295
1.33
Ｖ
VCS1D100P
Duty cycle =100%, VFB1=1.4V
1.38
Ｖ
VCS2D0N
Duty cycle =0%, VFB2=0.7V
1.33
Ｖ
Threshold voltage (CS2)
VCS2D20N
Duty cycle =20%, VFB2=0.7V
1.21
1.245
1.28
Ｖ
(Driving Nch-MOSFET)
VCS2D80N
Duty cycle =80%, VFB2=0.7V
0.85
0.885
0.92
Ｖ
VCS2D100N Duty cycle =100%, VFB2=0.7V
0.80
Ｖ
1.33
Ｖ
VCS2D0P
Duty cycle =0%, VFB2=0.7V
Threshold voltage (CS2)
VCS2D20P
Duty cycle =20%, VFB2=0.7V
1.20
1.235
1.27
Ｖ
(Driving Pch-MOSFET)
VCS2D80P
Duty cycle =80%, VFB2=0.7V
0.84
0.875
0.91
Ｖ
VCS2D100P
Duty cycle =100%, VFB2=0.7V
Ｖ
0.80
(5) Pulse width modulation (PWM) section (FB1・FB2 pin)
Item
Symbol
Test condition
MIN.
TYP.
MAX.
Unit
VFB1D0N
Duty cycle =0%, VCS1=VREG
0.82
Ｖ
Threshold voltage (FB1)
VFB1D20N
Duty cycle =20%, VCS1=VREG
0.925
Ｖ
(Driving Nch-MOSFET)
VFB1D80N
Duty cycle =80%, VCS1=VREG
1.285
Ｖ
VFB1D100N
Duty cycle =100%, VCS1=VREG
1.38
Ｖ
VFB1D0P
Duty cycle =0%, VCS1=VREG
0.82
Ｖ
VFB1D20P
Duty cycle =20%, VCS1=VREG
0.935
Ｖ
VFB1D80P
Duty cycle =80%, VCS1=VREG
1.295
Ｖ
VFB1D100P Duty cycle =100%, VCS1=VREG
1.38
Ｖ
VFB2D0N
Duty cycle =0%, VCS2=0V
1.33
Ｖ
Threshold voltage (FB2)
VFB2D20N
Duty cycle =20%, VCS2=0V
1.245
Ｖ
(Driving Nch-MOSFET)
VFB2D80N
Duty cycle =80%, VCS2=0V
0.885
Ｖ
0.80
Ｖ
Threshold voltage (FB1)
(Driving Pch-MOSFET)
VFB2D100N Duty cycle =100%, VCS2=0V
VFB2D0P
Duty cycle =0%, VCS2=0V
1.33
Ｖ
Threshold voltage (FB2)
VFB2D20P
Duty cycle =20%, VCS2=0V
1.235
Ｖ
(Driving Pch-MOSFET)
VFB2D80P
Duty cycle =80%, VCS2=0V
0.875
Ｖ
VFB2D100P
Duty cycle =100%, VCS2=0V
0.80
Ｖ
8
FA3687V
Quality is our message
(6) Timer latch protection section (CP pin)
Item
Symbol
Test condition
MIN.
TYP.
MAX.
Unit
Threshold voltage of FB1
VTHFB1TL
※6-1
1.5
―
2.0
V
Threshold voltage of FB2
VTHFB2TL
※6-2
0.2
―
0.6
V
Threshold voltage of CS1
VTHFB3TL
※6-3
0.2
―
0.6
V
Threshold voltage of CS2
VVTHCS1TL ※6-4
1.5
―
2.0
V
-2.4
-2.0
-1.5
μA
1.6
―
2.1
V
MIN.
TYP.
MAX.
Unit
2.0
2.2
2.35
V
Charge current of CP
Threshold voltage of CP
ICP
VCP=0.5V,VFB1=2.1V
VTHCPTL
(7) Under voltage lockout circuit section (VCC pin)
Item
ON threshold voltage of VCC
Hysteresis voltage
Symbol
Test condition
VUVLO
ΔVUVLO
0.1
V
(8) Output section (OUT1・OUT2･SEL1･SEL2 pin)
Item
High side on resistance
of OUT1/2
Low side on resistance
of OUT1/2
Symbol
RONHI
RONLO
Test condition
IOUT2=-50mA
MIN.
TYP.
10
MAX.
20
Unit
Ω
IOUT1=-50mA,VCC=5V
9
Ω
IOUT1=-50mA,VCC=15V
8
Ω
IOUT1=50mA
5
IOUT2=50mA,VCC=5V
5
Ω
IOUT2=50mA,VCC=15V
5
Ω
10
Ω
Rise time of OUT1/2
tRISE
CL=1000pF
25
ns
Fall time of OUT1/2
tFALL
CL=1000pF
40
ns
SEL pin voltage for driving
Nch-MOSFET
SEL pin voltage for driving
Pch-MOSFET
VSELN
0.0
―
0.2
Ｖ
VSELP
VREG-0.2
―
VREG
Ｖ
MIN.
TYP.
MAX.
Unit
3.5
mA
(9) Overall section
Item
Operating mode
supply current
Symbol
Test condition
ICCA
Ch.1, Ch.2 operating mode
2.5
ICCA1
Ch.1, Ch.2 off mode
2.0
mA
ICCA2
Ch.1, Ch.2 operating mode, Vcc=18V
3.0
mA
ICCA3
Latch mode
2.0
mA
*6-1: The current source of the CP pin operates when the voltage of FB1 exceeds the threshold voltage as shown in the
table.
*6-2: The current source of the CP pin operates when the voltage of FB2 falls below the threshold voltage as shown in the
table.
* 6-3: The timer latch of FB1 is disabled when the CS1 voltage is below the threshold voltage as shown in the table.
* 6-4: The timer latch of FB2 is disabled when the CS2 voltage is above the threshold voltage as shown in the table.
9
FA3687V
Quality is our message
7. Characteristic curves
Oscillation frequency vs.Timing resistor
Oscillation frequency vs. Supply voltage Vcc
Ta=25℃,RT=12kΩ(fosc=500kHz)
510
1600
508
Oscillation frequency [kHz]
Oscillation frequency [kHz]
Vcc=3.3V,Ta=25℃
1800
1400
1200
1000
800
600
400
506
504
502
500
498
496
494
492
200
490
0
1
10
Timing resistor R T[kΩ]
0
100
Oscillation frequency vs. ambient temperature
5
10
Vcc [V]
Vcc=3.3V,RT=12kΩ(fosc=500kHz)
Ta=25℃,RT=12kΩ(fosc=500kHz)
550
2.22
Regulated voltage V REG[V]
2.23
530
510
490
470
450
Load current
IREG=0A
2.21
2.20
2.19
2.18
2.17
430
-50
-25
0
25
50
75
100
Ambient temperature Ta [℃]
125
0
150
Regulated voltage vs. ambient temperature
5
10
Vcc[V]
15
20
Regulated voltage vs. load current
Vcc=3.3V,RT=12kΩ(fosc=500kHz)
Vcc=3.3V,RT =12kΩ(fosc=500kHz)
2.23
2.23
2.22
2.22
Regulated voltage V REG[V]
Oscillation frequency [kHz]
20
Regulated voltage vs. Supply voltage Vcc
570
Regulated voltage V REG[V]
15
2.21
2.20
2.19
2.18
2.17
Ta=85℃
2.21
2.20
Ta=25℃
2.19
Ta=-30℃
2.18
2.17
-50
-25
0
25
50
75
100
Ambient temperature Ta[℃]
125
150
0.0
10
0.2
0.4
0.6
0.8
Load current IREG[mA]
1.0
1.2
FA3687V
Quality is our message
Reference voltage vs. Supply voltage Vcc
Reference voltage vs. ambient temperature
Ta=25℃,RT=12kΩ(fosc=500kHz)
1.020
Vcc=3.3V,RT=12kΩ(fosc=500kHz)
1.020
1.015
Reference voltage V REF[V]
Reference voltage V REF [V]
1.015
1.010
1.005
1.000
0.995
0.990
0.985
1.010
1.005
1.000
0.995
0.990
0.985
0.980
0.980
0
5
10
15
20
25
-50
Vcc[V]
Error amp. Output current(sink) vs.
ambient temperature
-150
Vcc=3.3V,RT=12kΩ(fosc=500kHz)
4.5
4.0
3.5
3.0
2.5
2.0
-50
-25
0
25
50
75
100
Ambient temperature Ta[℃]
125
150
Vcc=3.3V,RT=12kΩ(fosc=500kHz)
-250
-300
-350
150
-50
-25
0
25
50
75
100
Ambient temperature Ta[℃]
125
150
Threshold voltage of CP vs. ambient temperature
Vcc=3.3V,RT=12kΩ(fosc=500kHz)
Vcc=3.3V,RT=12kΩ(fosc=500kHz)
2.3
2.2
Threshold voltage of CP [V]
Charge current of CP[uA]
125
-200
charge current of CP vs. ambient temperature
-1.0
0
25
50
75 100
Ambient temperature Ta[℃]
Error amp. Output current(source) vs.
ambient temperature
Output current (source) ISOFB[uA]
Output current (sink) ISIFB [mA]
5.0
-25
-1.5
-2.0
-2.5
2.1
2.0
1.9
1.8
1.7
1.6
-3.0
-50
-25
0
25
50
75
100
125
150
1.5
Ambient temperature Ta[℃]
-50
11
-25
0
25
50
75
100
Ambient temperature Ｔａ[℃]
125
150
FA3687V
Quality is our message
Output duty cycle vs.CS voltage (ch.1)
Output duty cycle vs.
Oscillation frequency (ch.1)
100
100
VCS1=1.35V
fosc=300kHz
90
90
fosc=500kHz
80
70
fosc=760kHz
60
fosc=1.5MHz
50
40
Driving Nch MOSFET
Vcc=3.3V，Ta=25℃
30
20
Output duty cycle (ch.1) [％]
Output duty cycle (ch.1) [％]
80
VCS1=1.30V
VCS1=1.25V
70
VCS1=1.20V
VCS1=1.15V
60
VCS1=1.10V
50
VCS1=1.05V
40
VCS1=1.00V
30
VCS1=0.95V
20
VCS1=0.90V
10
VCS1=0.85V
10
0
0.80
0.90
1.00
1.10
1.20
1.30
1.40
0
1.50
300
VCS1 [V]
500
Output duty cycle vs.CS voltage (ch.1)
700
900
1100
1300
oscillation frequency [ｋＨｚ]
1500
Output duty cycle vs.
Oscillation frequency (ch.1)
100
100
fosc=300kHz
90
fosc=500kHz
70
60
fosc=760kHz
50
fosc=1.5MHz
40
30
Driving Pch MOSFET
Vcc=3.3V，Ta=25℃
20
Output duty cycle (ch.1) [％]
80
Output duty cycle (ch.1) [％]
Driving Nch MOSFET
Vcc=3.3V，Ta=25℃
90
VCS1=1.35V
80
VCS1=1.30V
Driving Pch MOSFET
Vcc=3.3V，Ta=25℃
VCS1=1.25V
70
VCS1=1.20V
60
VCS1=1.15V
50
VCS1=1.10V
40
VCS1=1.05V
VCS1=1.00V
30
VCS1=0.95V
20
VCS1=0.90V
10
10
0
0.80
VCS1=0.85V
0.90
1.00
1.10
1.20
1.30
1.40
0
1.50
300
VCS1 [V]
12
500
700
900
1100
1300
Oscillation frequency [kHz]
1500
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Output duty cycle vs.CS voltage (ch.2)
100
Output duty cycle vs.
Oscillation frequency (ch.2)
100
fosc=300kHz
VCS2=0.80V
90
90
fosc=500kHz
Output duty cycle (ch.2) [％]
Output duty cycle (ch.2) [％]
Driving Nch MOSFET
Vcc=3.3V，Ta=25℃
70
fosc=760kHz
60
50
VCS2=0.85V
80
80
fosc=1.5MHz
40
30
VCS2=0.90V
70
VCS2=0.95V
60
VCS2=1.00V
VCS2=1.05V
50
VCS2=1.10V
40
VCS2=1.15V
30
VCS2=1.20V
20
20
VCS2=1.25V
10
10
VCS2=1.30V
0
0.70
0
0.80
0.90
1.00
1.10
VCS2 [V]
1.20
1.30
300
1.40
Output duty cycle vs. CS voltage (ch.2)
100
fosc=300kHz
80
fosc=500kHz
70
Driving Pch MOSFET
Vcc=3.3V，Ta=25℃
60
fosc=760kHz
50
40
fosc=1.5MHz
30
20
10
700
900
1100
1300
Oscillation frequency [kHz]
VCS2=0.80V
90
Output duty cycle (ch.2) [％]
Output duty cycle (ch.2) [％]
80
500
1500
Output duty cycle vs.
Oscillation frequency (ch.2)
100
90
0
0.70
Driving Nch MOSFET
Vcc=3.3V，Ta=25℃
Driving Pch MOSFET
Vcc=3.3V，Ta=25℃
VCS2=0.85V
70
VCS2=0.90V
60
VCS2=0.95V
VCS2=1.00V
50
VCS2=1.05V
40
VCS2=1.10V
30
VCS2=1.15V
20
VCS2=1.20V
VCS2=1.25V
10
VCS2=1.30V
0
0.80
0.90
1.00
1.10
VCS2 [V]
1.20
1.30
1.40
300
13
500
700
900
1100 1300
Oscillation frequency [kHz]
1500
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OUT1 terminal source current vs.
H level output voltage
0
OUT2 terminal source current vs.
H level output voltage
Ta=25℃
-50
-50
-100
-100
Vcc=2.5V
Vcc=2.5V
-150
IOUT2[mA]
IOUT1[mA]
-150
-200
Vcc= 3V
-250
-300
Vcc= 5V
-350
-200
Vcc= 3V
-250
-300
Vcc= 5V
-350
-400
-400
Vcc=12V
-450
Vcc=12V
-450
-500
-500
0.0
1.0
2.0
3.0
4.0
Vcc-VOUT1[V]
5.0
6.0
0.0
OUT1 terminal source current vs.
H level output voltage
Vcc=3.3V
0
1.0
2.0
3.0
Vcc-VOUT2[V]
4.0
OUT2 terminal source current vs.
H level output voltage
0
Vcc=3.3V
-100
IOUT2[mA]
-100
Ta=85℃
-150
Ta=25℃
-200
Ta=85℃
-150
-200
Ta=-30℃
Ta=25℃
Ta=-30℃
-250
-250
-300
-300
0.0
0.5
1.0
1.5
2.0
Vcc-VOUT1[V]
2.5
OUT1 terminal source currentvs.
H level output voltage
0.0
3.0
0
0
-100
-100
-200
-300
Ta=85℃
Ta=-30℃
-400
0.5
1.0
1.5
2.0
Vcc-VOUT2[V]
2.5
OUT2 terminal source current vs.
H level output voltage
Vcc=12V
IOUT2[mA]
IOUT1[mA]
5.0
-50
-50
IOUT1[mA]
Ta=25℃
0
3.0
Vcc=12V
-200
-300
Ta=85℃
Ta=-30℃
-400
Ta=25℃
Ta=25℃
-500
-500
0.0
1.0
2.0
3.0
Vcc-VOUT1[V]
4.0
5.0
0.0
14
1.0
2.0
3.0
Vcc-VOUT2[V]
4.0
5.0
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OUT1 terminal sink current vs. L level voltage
OUT2 terminal sink current vs. L level voltage
200
200
Ta=85℃
Ta=85℃
100
100
50
50
0
0
0.0
0.2
0.4
0.6
0.8
VOUT1[V]
1.0
1.2
0.0
1.4
OUT1 terminal Rise time vs. Supply voltage Vcc
Ta=25℃
30
Ta=-30℃
10
OUT2 terminal Rise time t RISE[ns]
OUT1 terminal Rise time t RISE[ns]
Ta=85℃
20
1.0
1.2
1.4
CL=1000pF
Ta=85℃
40
Ta=25℃
30
20
Ta=-30℃
10
0
0
5
10
Vcc[V]
15
20
0
OUT1 terminal Fall time vs. Supply voltage Vcc
10
Vcc[V]
15
20
CL=1000pF
Ta=25℃
100
Ta=-30℃
50
OUT2 terminal Fall time t
FALL [ns]
200
Ta=85℃
150
5
OUT2 terminal Fall time vs. Supply voltage Vcc
CL=1000pF
200
FALL [ns]
0.6
0.8
VOUT2[V]
50
0
OUT1 terminal Fall time t
0.4
60
50
40
0.2
OUT2 terminal Rise time vs. Supply voltage Vcc
CL=1000pF
60
Ta=25℃
Ta=-30℃
150
IOUT2[mA]
IOUT1[mA]
Ta=25℃
Ta=-30℃
150
Ta=85℃
150
Ta=25℃
100
Ta=-30℃
50
0
0
0
5
10
Vcc[V]
15
0
20
15
5
10
Vcc[V]
15
20
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Operating mode supply current vs.
Oscillation frequency
UVLO ON threshold vs. ambient temperature
Ta=25℃
2.5
Vcc=18V
Vcc=12V
5.0
Vcc=5V
4.0
3.0
Vcc=3.3V
Vcc=2.5V
UVLO ON threshold VUVLO[V]
Operating mode supply current I CCA[mA]
6.0
2.0
2.4
2.3
2.2
2.1
2.0
1.9
1.8
300
500
700
900
1100
1300
Oscillation frequency [kHz]
1500
-50
CS1 internal discharge switch current vs. voltage
-25
0
25
50
75
100
Ambient temperature Ta[℃]
Vcc=3.3V,RT=12kΩ(fosc=500kHz)
Vcc=3.3V,RT=12kΩ(fosc=500kHz)
0
Ta=-30℃
350
300
-50
Ta=25℃
250
ICS2off[uA]
ICS1off[uA]
150
CS2 internal discharge switch current vs. voltage
400
Ta=85℃
200
150
100
-100
Ta=85℃
-150
Ta=25℃
Ta=-30℃
50
0
0.00
125
-200
0.50
1.00
1.50
VCS1[V]
2.00
0.00
2.50
Error Amplifier Gain and Phase vs. frequency
16
0.50
1.00
V REG-VCS2[V]
1.50
2.00
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8. Description of each circuit
(1) Reference voltage circuit (VREF)
This circuit generates the reference voltage of 1.00V±1% compensated in temperature from VCC voltage, and is
connected to the non-inverting input of the error amplifier. The voltage cannot be observed directly because there is no
external pin for this purpose.
(2) Regulated Voltage circuit (VREG)
This circuit generates 2.20V±1% based on the reference voltage VREF, and is used as the power supply of the internal
IC circuits. The voltage is generated when the supply voltage, VCC, is input. The VREG voltage is also used as a
regulated power supply for Soft Start, Maximum Duty cycle limitation, and others. The output current for external circuit
should be within 1mA. A capacitor connected between VREG pin and GND pin is necessary to stabilize the VREG
voltage (To determine capacitance, refer to Recommended operating conditions). The VREG voltage is regulated in
VCC voltage of 2.4V or above.
(3) Oscillator
The oscillator generates a triangular waveform by charging and
discharging the built-in capacitor. A desired oscillation frequency can be set
by the value of the resistor connected to the RT pin (Fig. 1). The built-in
capacitor voltage oscillates between approximately 0.82V and 1.38V at
fosc=500kHz(that of ch1 and ch2 are slightly different) with almost the
same charging and discharging gradients (Fig. 2). You can set the desired
oscillation frequency by changing the gradients using the resistor
connected to the RT pin. (Large RT: low frequency, Small RT: high
frequency) The oscillator waveform cannot be
1.38V
observed from the outside because a pin for this
purpose is not provided. The RT pin voltage is
approximately 1V DC in normal operation. The 0.82V
oscillator output is connected to the PWM
comparator.
12
RT
RT
Fig.1
RT value: large
RT value: small
Fig.2
Vout1
RNF1
R1
Er.Amp.1
FB1
14
15
IN1‑
R2
+
(4) Error Amplifier Circuit
The error amplifier 1 has the inverting input of IN1(-) pin (Pin14).
The non-Inverting input is internally connected to the reference
voltage VREF (1.00V±1%; 25℃). The error amplifier 2 has the
inverting input IN2(-) pin (Pin4) and non-inverting input IN2(+)
pin (Pin5) externally. Since each input of error amplifier 2 is
connected to the pins, CH2 is suitable for any circuit topology.
The FB pins (Pin3, Pin15) are the output of the error amplifier.
An external RC network is connected between FB pin and INpin for gain and phase compensation setting. (Fig. 3) For
connecting of each topology, see Design Advice.
OSC
VREF
(1.0V)
Vout2
Comp
VREG
13
R3
R5
Er.Amp.2
IN2+
Comp
FB2
5
IN2‑
R4
3
4
R6
RNF2
Fig.3
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(5) PWM comparator
The PWM output generates from the oscillator
output, the error amplifier output (FB1, FB2)
and CS voltage (CS1, CS2) (Fig. 4). The
FB1
oscillator output is compared with the preferred
lower voltage between FB1 and CS1 for ch1.
While the preferred voltage is lower than
Oscillato
oscillator output, the PWM output is low. While
r
the preferred voltage is higher than oscillator
output
output, the PWM output is high. Since the
phase of Ch2 is the opposite phase of Ch1,
higher voltage between FB2 and CS2 is
preferred and while the preferred voltage is
FB2
lower than the oscillator output, the PWM
output 2 is high. (Cannot be observed
externally) The output polarity of OUT1, OUT2
changes according to the condition of SEL pin. (See Fig. 6)
PWM output1
PWM
Comp.1
N/P ch.
drive
CS1
OUT1
9
16
SEL1
UVLO
CS2
PWM output2
N/P ch.
drive
PWM
Comp.2
OUT2
8
2
SEL2
Fig.4
(6) Soft start function
This IC has a soft start function to protect DC-to-DC converter circuits from damage when starting operation. CS1 pin
(Pin10), and CS2 pin (Pin7) are used for soft start function of ch1 and ch2 respectively. (Fig. 5) When the supply
voltage is applied to the VCC pin and UVLO is cancelled,
VREG
VREG
capacitor CCS1 and CCS2 is charged by VREG through the
R7
13
13
resistor R7 or R9. Therefore, CS1 voltage gradually
CCS2
10
increases and CS2 voltage gradually decreases. Since CS1
7
CS2
CS1
C
CS1
and CS2 pin are connected to the PWM comparator
R9
internally, the pulses gradually widen and then the soft start
Fig.5
function operates. (Fig. 6)
The maximum duty cycle can be set by using the CS pins. (See Design Advice about the detail)
Er.Amp.1 output
Oscillator output
PWM output 1
OUT1
Pch.drive
(SEL1：VREG)
OUT1
Nch.drive
(SEL1：GND)
ＣＳ2 pin voltage
CS1 pin voltage
Oscillator output
PWM output2
OUT2
Pch.drive
(SEL2：VREG)
OUT2
Nch.drive
(SEL2：GND)
Fig.6
18
Er.Amp.2 output
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(7) Timer latch short-circuit protection circuit
This IC has the timer latch short-circuit protection circuit. This circuit cuts off
the output of all channels when the output voltage of DC-to-DC converter
drops due to short circuit or overload. To set delay time for timer latch
operation, a capacitor CCP should be connected to the CP pin (Fig. 7). When
one of the output voltage of the DC-to-DC converter drops due to short circuit
or overload, the FB1 pin voltage increases up to around the VREG voltage for
Icp
Vcp
1
CP
CCP
Fig.7
CP pin voltage [V]
ch 1, or the FB2 pin voltage drops down to
momentary
short
around 0 V for ch 2.When FB1 pin voltage
circuit
short circuit
exceeds 2.0V(max.) or FB2 pin voltage
VREG pin voltag
2.1V(max)
falls below 0.2V(min.), constant-current
2.0
source (2 μ A typ.) starts charging the
Start-up
capacitor CCP connected to the CP pin. If
short circuit
the voltage of the CP pin exceeds 2.1 V
protection
1.0
(max.), the circuit regards the case as
tp
abnormal. Then the IC is set to off latch
mode and the output of all channels is shut
Time t
off, (Fig. 8) and the current consumption
Fig.8
become 2mA(typ.) The period (tp) between
the occurrence of short-circuit in the converter output and setting to off latch mode can be calculated by the following
equation:
tp[ s ] = CCP *
VTHCPTL
ICP
VTHCPTL: CP pin latched mode threshold voltage [V]
ICP: CP charge source current [μA]
CCP: capacitance of CP pin capacitor
You can reset off latched mode of the short-circuit protection by either of the following ways about 1) CP pin, or 2) VCC
pin, or 3) CS1or CS2 pin:
1) CP voltage = 0V
2) VCC voltage UVLO voltage (2.2V, typ.) or below
3) Set the CS pin of the cause of OFF latched mode as follows
CS1 pin voltage = 0V, CS2 pin voltage = VREG
If the timer-latched mode is not necessary, connect the CP pin to GND.
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(8) Output circuit
The IC contains a push-pull output stage and can directly drive MOSFETs. The maximum peak current of the output
stage is sink current of +150mA, and source current of - 400mA. The IC can also drive NPN and PNP transistors. The
maximum current in such cases is ± 50mA. You must design the output current considering the rating of power
dissipation. (See Design Advice)
You can switch the types of external discrete MOSFETs by wiring of the SEL pins (Pin 2, Pin 16). For driving Nch MOS,
connect the SEL pins to GND. For driving Pch MOS, connect the SEL pins to VREG. You can design buck converter
or inverting converter by driving Pch MOS, and boost converter by driving Nch MOS.
Connect them either to GND or to VREG surely.
(9) Under voltage lockout circuit
The IC contains a under voltage lockout circuit to protect the circuit from the damage caused by malfunctions when the
supply voltage drops. When the supply voltage rises from 0V, the IC starts to operate at VCC of 2.2V(typ.) and outputs
generate pulses. If a drop of the supply voltage occurs, it stops output at VCC of 2.1V(typ.). When it occurs, the CS1 pin
is turned to low level and the CS2 pin to high level, and then these pins are reset.
20
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9. Design Advice
(1) Setting the oscillation frequency
As described at Section 8-(1), “Description of Each Circuit,” a desired oscillation frequency can be determined by the
value of the resistor connected to the RT pin. When designing an oscillation frequency, you can set any frequency
between 300kHz and 1.5MHz. You can obtain the oscillation frequency from the characteristic curve “Oscillation
frequency (fosc) vs. timing resistor resistance (RT)” or the value can be approximately calculated by the following
expression.
fosc = 4050 * RT −0.86
1.16
4050
RT =
fosc
fosc: oscillation frequency [kHz]
RT: timing resistor [kΩ]
This expression, however, can be used for rough calculation, the obitained value is not guaranteed. The operation
frequency varies due to the conditions such as tolerance of the characteristics of the ICs, influence of noises, or external
discrete components. When determining the values, examine the effectiveness of the values in an actual circuit. The
timing resistor RT should be wired to the GND pin as shortly as possible because the RT pin is a high impedance pin and
is easy affected by noises.
(2) Operation near the maximum or the minimum output duty cycle
As described in “Output duty cycle vs. voltage”, the output duty cycle of this IC changes sharply near the minimum and
the maximum output duty cycle. Note that these phenomena are conspicuous for high frequency operation (when the
pulse width is narrow).
(3) Determining soft start period
The period from the start of charging the capacitor CCS to widening n% of output duty cycle can be roughly calculated
by the following expression: (see Fig. 5 for symbols)
VCS1n
t[ms] = − R7 * CCS1 * ln1 −
VREG
VCS 2 n
t[ms] = − R9 * CCS 2 * ln
VREG
for CS1 pin
for CS2 pin
CCS1, CCS2: Capacitance connected to CS1or CS2 pin [μF]
R7, R9: Resistance connected to CS1 or CS2 pin [kΩ]
VCS1n and VCS2n are the voltage of the CS1 and CS2 pins in n% of output duty cycle, and vary in accordance with
operating frequency. The value can be obtained from the characteristic curve “Output duty cycle vs. CS voltage”
To reset the soft start function, the supply voltage VCC is lowered below the UVLO voltage (2.1V typ.) and then the
internal switch discharges the CS capacitor. The characteristics of the internal switch for discharge are shown in
following the characteristics curves of “Characteristics of CS1 internal discharge switch current vs. voltage” and
“Characteristics of CS2 internal discharge switch current vs. voltage”. Therefore, when determining the period of soft
start at restarting the power supply, consider the characteristics carefully.
21
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(4) Setting Maximum Duty Cycle
As described in the Fig. 9, you can limit maximum duty
VREG
VREG
R7
CCS2
13
13
cycle by connecting a resistor divider "R7, R8 or R9,
R10" between CS1, CS2 and VREG pin. Set the
R10
10
7
maximum duty cycle considering that relation between
CS2
CS1
the maximum output duty cycle and the CS pin
R8
R9
CCS1
voltage changes with operation frequency as
Fig.9
described in the characteristics curves of “Output duty
cycle vs. Oscillation frequency” and “Output duty cycle vs. CS voltage”. When the maximum duty cycle is limited, CS
pin voltage at start-up is described in Fig. 10, and the approximate value of soft start period can be obtained by the
following expressions:
VCC
VCC
Threshold voltage
R8
R7 + R8
VREG pin voltage
Threshold voltage
⋅ VREG
VCS1n
VCS2n
R9
R9 + R10
ｔ0
⋅ VREG
ｔ
ｔ0
ｔ
t0: Time from power-on of VCC to reaching unlock voltage of UVLO
Fig.10
VCS1n
t[ms] = − R 0 * CCS1 * ln1 −
VCS1
R0 =
R7 * R8
R7 + R8
for CS1
The divided CS1 voltage is obtained by:
VCS1 =
R8
* VREG
R7 + R8
VCS 2 n − VCS 2
t[ms] = − R 0 * CCS 2 * ln
VREG − VCS 2
R0 =
R9 * R10
R9 + R10
for CS2
The divided CS2 voltage is obtained by:
VCS 2 =
R9
* VREG
R9 + R10
CCS1, CCS2: Capacitance connected to the CS1 or CS2 pin [μF]
R7, R8, R9, R10: Resistance connected to CS1 or CS2 pin [kΩ]
VCS1n and VCS2n are the voltages of CS1 and CS2 under a certain output duty cycle and varies with operation
frequencies. The values of VCS1n and VCS2n can be obtained from the characteristics curve of “Output duty cycle vs.
CS voltage”.
The charging of CCS1 and CCS2 after UVLO is unlocked.
Therefore, the period from power-on of Vcc to widening n% of output duty cycle is the sum of t0 and t
22
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(5) Determining the output voltage of DC-DC converters
The ways to determine the output voltage of the DCch1
DC converter of each channel is shown in Fig. 10
and the following equations.
OUT1
Vout1
9
SEL1
For ch1:
The positive output voltage of DC-to-DC converter
(a buck, a boost) is determined by:
Vout1
IN1‑
14
15
VREF
(1.0V)
For ch2:
The positive output voltage of DC-to-DC converter is
determined by:
buck
OUT1
Vout1
9
Vout1
SEL1
16
R1
IN1‑
14
R3 + R 4
Vout 2 = V 1 *
R3
15
GND
FB1
boost
+
R6
R5 + R 6
FB1
+
R2
R1 + R 2
Vout1 =
* VREF
R2
Here,V 1 = VREG *
VREG
16
R1
R2
VREF
(1.0V)
ch2
OUT2
8
Vout2
When R5=R6,
VREG
SEL2
13
R3 + R 4
Vout 2 = VREG *
2 R3
R4
IN2+
Vout2
FB2
5
IN2‑
V1
R3
3
4
buck
R6
The negative output voltage of DC-to-DC converter
(inverting) is determined by:
Vout 2 =
VREG
2
R5
OUT2
8
R3 + R 4
R4
*V1 −
* VREG
R3
R3
Vout2
Vout2
VREG
SEL2
13
2
R4
R5
IN2+
FB2
5
The ratio of resistances is determined by:
V1
R3
R3 VREG − V 1
=
R 4 Vout 2 + V 1
IN2‑
GND
3
4
boost
R6
(Use the absolute value of the Vout2 voltage.)
OUT2
8
VREG
SEL2
13
When R5=R6,
VREG
Vout2
2
R3
R3 − R 4
Vout 2 = VREG *
2 R3
R5
V1
IN2+
FB2
5
3
4
R4
Connect the SEL1 and SEL2 pin to GND or VREG
surely.
Vout2
R6
IN2‑
inverting
Fig.11
(6) Restriction of external discrete components and Recommended operating conditions
To achieve a stable operation of the IC, the value of external discrete components connected to VCC, VREG, CS, CP
pins should be within the recommended operating conditions. And the voltage and the current applied to each pin
should be also within the recommended operating conditions. If the pin voltage of OUT1, OUT2, or VREG becomes
higher than the VCC pin voltage, the current flows from the pins to the VCC pin because parasitic three diode exist
between the VCC pin and these pins. Be careful not to allow this current to flow.
23
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(5) 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 ICCA, 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*(ICCA+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)
ICCA=2.5mA for VCC=3.3V in the case of a typical IC from the characteristics curve. Qg=6nC, fsw=500kHz, the IC
loss ”Pd” is as follows.
Pd≒3.3*(2.5mA+6nC*500kHz)≒18.2mW
if two MOSFETs are driven under the same condition for 2 channels, Pd is as follows:
Pd≒3.3*{2.5mA+2*(6nC*500kHz)}=28.1mW
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FA3687V
Quality is our message
10.Application circuit
5V/500mA
7to18V
40kΩ
10uF
GND
10uF
GND
10kΩ
0.1uF
0.01uF
VCC CS2 OUT2
6
8
7
22kΩ
100Ω
10uF
0.47uF
11kΩ
IN2- IN2+
4
5
FA3687V
12
RT
0.01uF
10kΩ
1MΩ
FB2
3
SEL2
2
10kΩ
13
14
IN1- VREG
1uF
16
15
SEL1 FB1
6.2kΩ
3.3V/500mA
10kΩ
0.01uF
10kΩ
CP
1
100kΩ
11
10
9
GND CS1 OUT1
0.1uF
100kΩ
0.068uF
25