ssc3s921 ds en

LLC Current-Resonant Off-Line Switching Controller
SSC3S921
Data Sheet
Description
Package
The SSC3S921 is a controller with SMZ* method for
LLC current resonant switching power supplies,
incorporating a floating drive circuit for a high-side
power MOSFET. The product includes useful functions
such as Standby Function, Automatic Dead Time
Adjustment, and Capacitive Mode Detection.
The product achieves high efficiency, low noise and
high cost-performance power supply systems with few
external components.
*SMZ: Soft-switched Multi-resonant Zero Current
switch, achieved soft switching operation during all
switching periods.
SOP18
Not to scale
Features
● Standby Mode Change Function
▫ Output Power at Light Load: PO = 125 mW
(PIN = 0.27 W, as a reference with discharge resistor
of 1MΩ for across the line capacitor)
▫ Burst operation in standby mode
▫ Soft-on/Soft-off function: reduces audible noise
● PFC IC ON/OFF Function: In standby operation, the IC
turns off PFC IC.
● Soft-start Function
● Capacitive Mode Detection Function
● Reset Detection Function
● Automatic Dead Time Adjustment Function
● Brown-In and Brown-Out Function
● Input Electrolytic Capacitor Discharge Function
● Protections
▫ High-side Driver UVLO : Auto-restart
▫ Overcurrent Protection (OCP) : Auto-restart, peak
drain current detection, 2-step detection
▫ Overload Protection (OLP) : Auto-restart
▫ Overvoltage Protection (OVP) : Auto-restart
▫ REG Overvoltage Protection (REG_OVP) : Latched
shutdown
▫ Thermal Shutdown (TSD) : Auto-restart
Applications
Switching power supplies for electronic devices such as:
● Digital appliances: LCD television and so forth
● Office automation (OA) equipment: server, multifunction printer, and so forth
● Industrial apparatus
● Communication facilities
Typical Application
VOUT1(+)
U1
PFC OUT
VSEN
GND
1
18
VCC
2
17
FB
3
16
VGH
15
VS
14
VB
ADJ
4
CSS
5
CL
6
RC
7
PL
SB
SSC3S921
PFC IC
(SSC2016S)
VCC
ST
VOUT(-)
13
12
REG
8
11
VGL
9
10
GND
VOUT2(+)
TC_SSC3S921_1_R4
SSC3S921 - DSJ Rev.1.5
SANKEN ELECTRIC CO.,LTD.
Apr. 01, 2016
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2015
1
SSC3S921
CONTENTS
Description ------------------------------------------------------------------------------------------------------ 1
CONTENTS ---------------------------------------------------------------------------------------------------- 2
1. Absolute Maximum Ratings ----------------------------------------------------------------------------- 3
2. Electrical Characteristics -------------------------------------------------------------------------------- 4
3. Block Diagram --------------------------------------------------------------------------------------------- 7
4. Pin Configuration Definitions --------------------------------------------------------------------------- 7
5. Typical Application --------------------------------------------------------------------------------------- 8
6. External Dimensions -------------------------------------------------------------------------------------- 9
7. Marking Diagram ----------------------------------------------------------------------------------------- 9
8. Operational Description ------------------------------------------------------------------------------- 10
8.1 Resonant Circuit Operation --------------------------------------------------------------------- 10
8.2 Startup Operation --------------------------------------------------------------------------------- 13
8.3 Undervoltage Lockout (UVLO) ---------------------------------------------------------------- 13
8.4 Bias Assist Function------------------------------------------------------------------------------- 13
8.5 Soft Start Function -------------------------------------------------------------------------------- 14
8.6 Minimum and Maximum Switching Frequency Setting ----------------------------------- 14
8.7 High-side Driver ----------------------------------------------------------------------------------- 15
8.8 Constant Voltage Control Operation ---------------------------------------------------------- 15
8.9 Standby Function ---------------------------------------------------------------------------------- 16
8.9.1
Standby Mode Changed by External Signal ------------------------------------------- 16
8.9.2
Burst Oscillation Operation --------------------------------------------------------------- 16
8.9.3
PFC ON/OFF Function -------------------------------------------------------------------- 17
8.10 Automatic Dead Time Adjustment Function ------------------------------------------------ 17
8.11 Brown-In and Brown-Out Function ----------------------------------------------------------- 18
8.12 Capacitive Mode Detection Function ---------------------------------------------------------- 19
8.13 Input Electrolytic Capacitor Discharge Function ------------------------------------------- 20
8.14 Reset Detection Function ------------------------------------------------------------------------ 20
8.15 Overvoltage Protection (OVP) ------------------------------------------------------------------ 22
8.16 REG Overvoltage Protection (REG_OVP) --------------------------------------------------- 22
8.17 Overcurrent Protection (OCP) ----------------------------------------------------------------- 22
8.18 Overload Protection (OLP)---------------------------------------------------------------------- 23
8.19 Thermal Shutdown (TSD) ----------------------------------------------------------------------- 23
9. Design Notes ---------------------------------------------------------------------------------------------- 24
9.1 External Components ---------------------------------------------------------------------------- 24
9.1.1
Input and Output Electrolytic Capacitors ---------------------------------------------- 24
9.1.2
Resonant Transformer --------------------------------------------------------------------- 24
9.1.3
Current Detection Resistor, ROCP -------------------------------------------------------- 24
9.1.4
Current Resonant Capacitor, Ci --------------------------------------------------------- 24
9.1.5
Gate Pin Peripheral Circuit --------------------------------------------------------------- 24
9.2 PCB Trace Layout and Component Placement --------------------------------------------- 24
10. Pattern Layout Example ------------------------------------------------------------------------------- 26
IMPORTANT NOTES ------------------------------------------------------------------------------------- 28
SSC3S921 - DSJ Rev.1.5
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Apr. 01, 2016
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© SANKEN ELECTRIC CO.,LTD. 2015
2
SSC3S921
1.
Absolute Maximum Ratings
● The polarity value for current specifies a sink as "+," and a source as "−," referencing the IC.
● Unless otherwise specified, TA is 25°C
Characteristic
Symbol
Pins
Rating
Unit
VSEN Pin Sink Current
ISEN
1 − 10
1.0
mA
Control Part Input Voltage
VCC
2 − 10
− 0.3 to 35
V
FB Pin Voltage
VFB
3 − 10
− 0.3 to 6
V
ADJ Pin Voltage
VADJ
4 − 10
− 0.3 to VREG
V
CSS Pin Voltage
VCSS
5 − 10
− 0.3 to 6
V
CL Pin Voltage
VCL
6 − 10
− 0.3 to 6
V
RC Pin Voltage
VRC
7 − 10
− 6 to 6
V
PL Pin Voltage
VPL
8 − 10
− 0.3 to 6
V
SB Pin Sink Current
ISB
9 − 10
100
μA
VGL pin Voltage
VGL
11 − 10
− 0.3 to VREG + 0.3
V
REG pin Source Current
IREG
12 − 10
− 10.0
mA
VB−VS
14 − 15
− 0.3 to 20.0
V
VS Pin Voltage
VS
15 − 10
− 1 to 600
V
VGH Pin Voltage
VGH
16 − 10
VS− 0.3 to VB + 0.3
V
ST Pin Voltage
VST
18 − 10
− 0.3 to 600
V
Operating Ambient Temperature
TOP
−
− 40 to 85
°C
Storage Temperature
Tstg
−
− 40 to 125
°C
Voltage Between VB Pin and VS Pin
Tj
−
150
°C
Junction Temperature
* Surge voltage withstand (Human body model) of No.14, 15 and 16 is guaranteed 1000V. Other pins are guaranteed
2000V.
SSC3S921 - DSJ Rev.1.5
SANKEN ELECTRIC CO.,LTD.
Apr. 01, 2016
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2015
3
SSC3S921
2.
Electrical Characteristics
● The polarity value for current specifies a sink as "+," and a source as "−," referencing the IC.
● Unless otherwise specified, TA is 25 °C, VCC is 19 V
Characteristic
Symbol
Conditions
Pins
Min.
Typ.
Max.
Unit
Start Circuit and Circuit Current
Operation Start Voltage
VCC(ON)
2 − 10
15.8
17.0
18.2
V
Operation Stop Voltage*
Startup Current Biasing Threshold
Voltage*
Circuit Current in Operation
VCC(OFF)
2 − 10
7.8
8.9
9.8
V
VCC(BIAS)
2 − 10
9.0
9.8
10.6
V
ICC(ON)
2 − 10
−
−
10.0
mA
Circuit Current in Non-operation
ICC(OFF)
2 − 10
0.7
1.5
mA
Startup Current
Protection Operation Release
Threshold Voltage*
REG Pin Overvoltage Protection
Release Threshold Voltage
Circuit Current in Protection
ICC(ST)
18 − 10
－
3.0
6.0
9.0
mA
VCC(P.OFF)
2 − 10
7.8
8.9
9.8
V
VCC(L.OFF)
2 − 10
2.0
5.0
8.0
V
2 − 10
−
0.7
1.5
mA
27.5
31.5
35.5
kHz
230
300
380
kHz
0.04
0.24
0.44
µs
1.20
1.65
2.20
µs
69
73
77
kHz
42.4
45.4
48.4
kHz
ICC(P)
VCC = 11 V
VCC = 10 V
Oscillator
Minimum Frequency
f(MIN)
Maximum Frequency
f(MAX)
Minimum Dead-Time
td(MIN)
Maximum Dead-Time
td(MAX)
Externally Adjusted Minimum
Frequency 1
Externally Adjusted Minimum
Frequency 2
Feedback Control
FB Pin Oscillation Start Threshold
Voltage
FB Pin Oscillation Stop Threshold
Voltage
FB Pin Maximum Source Current
f(MIN)ADJ1
RCSS = 30 kΩ
f(MIN)ADJ2
RCSS = 77 kΩ
11 – 10
16 − 15
11 – 10
16 − 15
11 – 10
16 − 15
11 – 10
16 − 15
11 – 10
16 − 15
11 – 10
16 − 15
VFB(ON)
3 – 10
0.15
0.30
0.45
V
VFB(OFF)
3 – 10
0.05
0.20
0.35
V
3 – 10
− 300
− 195
− 100
µA
IFB(R)
3 – 10
2.5
5.0
7.5
mA
CSS Pin Charging Current
ICSS(C)
5 – 10
− 120
− 105
− 90
µA
CSS Pin Reset Current
ICSS(R)
5 – 10
11 – 10
16 − 15
1.1
1.8
2.5
mA
400
500
600
kHz
FB Pin Reset Current
IFB(MAX)
VFB = 0 V
Soft-start
Maximum Frequency in Soft-start
f(MAX)SS
VCC = 11V
Standby
SB Pin Standby Threshold Voltage
SB Pin Oscillation Start Threshold
Voltage
SB Pin Oscillation Stop Threshold
Voltage
VSB(STB)
9 – 10
4.5
5.0
5.5
V
VSB(ON)
9 – 10
0.5
0.6
0.7
V
VSB(OFF)
9 – 10
0.4
0.5
0.6
V
* VCC(OFF) = VCC(P.OFF) < VCC(BIAS) always.
SSC3S921 - DSJ Rev.1.5
SANKEN ELECTRIC CO.,LTD.
Apr. 01, 2016
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© SANKEN ELECTRIC CO.,LTD. 2015
4
SSC3S921
Characteristic
Pins
Min.
Typ.
Max.
Unit
SB Pin Clamp Voltage
VSB(CLAMP)
Symbol
Conditions
9 – 10
7
8.5
10
V
SB Pin Source Current
ISB(SRC)
9 – 10
− 17
− 10
−3
µA
SB Pin Sink Current
CSS Pin Standby Release Threshold
Voltage
PFC ON/OF Function
ADJ Pin Voltage in Normal
Operation
ADJ Pin Voltage in Standby
Operation
Overload Protection (OLP)
ISB(SNK)
9 – 10
3
10
17
µA
VCSS(STB)
5 – 10
1.35
1.50
1.65
V
VADJ(L)
IADJ = 100 μA
4 – 10
0
1
2
V
VADJ(H)
IADJ = −100 μA
4 – 10
8.5
9.9
10.8
V
CL pin OLP Threshold Voltage
VCL(OLP)
6 – 10
3.9
4.2
4.5
V
CL Pin Source Current
ICL(SRC)
6 – 10
− 29
− 17
−5
μA
VSEN Pin Threshold Voltage (On)
VSEN(ON)
1 – 10
1.248
1.300
1.352
V
VSEN Pin Threshold Voltage (Off)
VSEN(OFF)
1 – 10
1.056
1.100
1.144
V
VSEN (CLAMP)
1 – 10
10.0
–
–
V
tRST(MAX)
11 – 10
16 − 15
4
5
6
µs
VREG
12 – 10
9.6
10.0
10.8
V
VBUV(ON)
14 – 15
5.7
6.8
7.9
V
VBUV(OFF)
14 – 15
5.5
6.4
7.3
V
11 – 10
16 − 15
–
– 540
–
mA
11 – 10
16 − 15
–
1.50
–
A
11 – 10
16 − 15
− 140
− 90
− 40
mA
11 – 10
16 − 15
140
230
360
mA
0.02
0.10
0.18
V
− 0.18
− 0.10
− 0.02
V
0.4
0.50
0.6
V
− 0.6
− 0.50
− 0.4
V
Brown-In and Brown-Out
VSEN Pin Clamp Voltage
Reset Detection
Maximum Reset Time
Driver Circuit Power Supply
VREG Pin Output Voltage
High-side Driver
High-side Driver Operation Start
Voltage
High-side Driver Operation Stop
Voltage
Driver Circuit
VGL,VGH Pin Source Current 1
IGL(SRC)1
IGH(SRC)1
VGL,VGH Pin Sink Current 1
IGL(SNK)1
IGH(SNK)1
VGL,VGH Pin Source Current 2
IGL(SRC)2
IGH(SRC)2
VGL,VGH Pin Sink Current 2
IGL(SNK)2
IGH(SNK)2
VREG = 10.5V
VB = 10.5V
VGL = 0V
VGH = 0V
VREG = 10.5V
VB = 10.5V
VGL = 10.5V
VGH = 10.5V
VREG = 11.5V
VB = 11.5V
VGL = 10V
VGH = 10V
VREG = 12V
VB = 12V
VGL = 1.5V
VGH = 1.5V
Current Resonant and Overcurrent Protection (OCP)
Capacitive Mode Detection Voltage 1
VRC1
7 – 10
Capacitive Mode Detection Voltage 2
VRC2
7 – 10
SSC3S921 - DSJ Rev.1.5
SANKEN ELECTRIC CO.,LTD.
Apr. 01, 2016
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2015
5
SSC3S921
Characteristic
Symbol
Conditions
Pins
Min.
Typ.
Max.
Unit
1.42
1.50
1.58
V
− 1.58
− 1.50
− 1.42
V
2.15
2.30
2.45
V
− 2.45
− 2.30
− 2.15
V
RC Pin Threshold Voltage (Low)
VRC(L)
7 – 10
RC Pin Threshold Voltage
(High speed)
VRC(S)
7 – 10
CSS Pin Sink Current (Low)
ICSS(L)
5 – 10
1.1
1.8
2.5
mA
CSS Pin Sink Current (High speed)
ICSS(S)
5 – 10
13.0
20.5
28.0
mA
VCC Pin OVP Threshold Voltage
VCC(OVP)
2 – 10
30.0
32.0
34.0
V
REG Pin OVP Threshold Voltage
VCC(REG)
12 – 10
11.5
12.4
13.5
V
Tj(TSD)
−
140
–
–
°C
θj-A
−
−
−
95
°C/W
Overvoltage Protection (OVP)
Thermal Shutdown (TSD)
Thermal Shutdown Temperature
Thermal Resistance
Junction to Ambient Thermal
Resistance
SSC3S921 - DSJ Rev.1.5
SANKEN ELECTRIC CO.,LTD.
Apr. 01, 2016
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2015
6
SSC3S921
3.
Block Diagram
ST
18
High Side Driver
STARTUP
14
VB
UVLO
VCC
GND
VSEN
SB
FB
CSS
2
16
START/STOP/
REG/BIAS/
OVP
LEVEL
SHIFT
15
10
VCC
GND
1
9
3
5
VGH
VS
INPUT
SENSE
12
REG
11
VGL
MAIN
STANDBY
CONTROL
RC DETECTOR
FB
CONTROL
FREQ.
CONTROL
SOFT-START/
OC/FMINADJ
DEAD
TIME
RV DETECTOR
FREQ.
MAX
OC DETECTOR
7
6
PL DETECTOR/
OLP
8
PFC ON/OFF
4
RC
CL
PL
ADJ
BD_SSC3S921_R3
4.
Pin Configuration Definitions
1
VSEN
ST 18
2
VCC
3
FB
4
ADJ
VS 15
5
CSS
VB 14
6
CL
7
RC
REG 12
8
PL
VGL 11
9
SB
GND 10
VGH 16
Number
1
Name
VSEN
2
VCC
3
4
5
6
FB
ADJ
CSS
CL
7
RC
8
9
10
11
12
13
14
15
16
17
18
PL
SB
GND
VGL
REG
−
VB
VS
VGH
(NC)
ST
Functions
The mains input voltage detection signal input
Supply voltage input for the IC, and Overvoltage
Protection (OVP) signal input
Feedback signal input for constant voltage control
PFC ON/OFF signal output
Soft-start capacitor connection
Load current detection capacitor connection
Resonant current detection signal input, and
Overcurrent Protection (OCP) signal input
Resonant current detection signal input for OLP
Standby mode change signal input
Ground
Low-side gate drive output
Supply voltage output for gate drive circuit
(Pin removed)
Supply voltage input for high-side driver
Floating ground for high-side driver
High-side gate drive output
−
Startup current input
SSC3S921 - DSJ Rev.1.5
SANKEN ELECTRIC CO.,LTD.
Apr. 01, 2016
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2015
7
SSC3S921
5.
Typical Application
PFC OUT
R2
C1
T1
R3
D53
C55
VOUT1(+)
R4
R51
U1
GND
C4
1
18
VCC
2
17
FB
3
16
ADJ
4
CSS
5
C5
CADJ
R5
C6
CL
C7
RC
C8
PL
RADJ1
PFC IC
(SSC2016S)
VCC
ROCP
R6
R7
RADJ2
SB
6
7
8
9
SSC3S921
VSEN
15
14
ST
Q(H)
VGH
C12 R10
VS
R11
VB
D4
13
12
PC1
C52
D51
R15 D5
REG
11
VGL
10
GND
R55
R56
C53
Q1
R8
PC1
R53
VOUT(-)
C51
R12
D3
R16 D6 Q(L)
CV
D52
VOUT2(+)
Ci
R58
C3
R13
D54
PC2
R14
C9
C10
R15
R1
R16
C11
R54
R57 C54
Standby
Q51
QC
R52
D1
C2
R59
R17
PC2
TC_SSC3S921_3_R4
Figure 5-1 Typical application
SSC3S921 - DSJ Rev.1.5
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Apr. 01, 2016
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© SANKEN ELECTRIC CO.,LTD. 2015
8
SSC3S921
6.
External Dimensions
● SOP18
NOTES:
● Dimension is in millimeters
● Pb-free. Device composition compliant with the RoHS
directive
7.
Marking Diagram
18
SSC3S921
Part Number
SKYMD
XXXX
1
Lot Number
Y is the last digit of the year (0 to 9)
M is the month (1 to 9, O, N or D)
D is a period of days (1 to 3):
1 : 1st to 10th
2 : 11th to 20th
3 : 21th to 31st
Control Number
SSC3S921 - DSJ Rev.1.5
SANKEN ELECTRIC CO.,LTD.
Apr. 01, 2016
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© SANKEN ELECTRIC CO.,LTD. 2015
9
SSC3S921
8.
Operational Description
All of the parameter values used in these descriptions
are typical values, unless they are specified as minimum
or maximum. With regard to current direction, "+"
indicates sink current (toward the IC) and "–" indicates
source current (from the IC).
Q(H) and Q(L) indicate a high-side power MOSFET and
a low-side power MOSFET respectively. Ci, and CV
indicate a current resonant capacitor and a voltage
resonant capacitor respectively.
8.1
Resonant Circuit Operation
Figure 8-1 shows a basic RLC series resonant circuit.
R
L
C
Figure 8-1 RLC series resonant circuit
The impedance of the circuit, Ż, is as the following
Equation.
(1)
The frequency in which Ż becomes minimum value is
the resonant frequency, f0. The higher frequency area
than f0 is the inductance area, and the lower frequency
area than f0 is the capacitance area.
From Equation (3), f0 is as follows;
(4)
Figure 8-3 shows the circuit of a current resonant
power supply. The basic configuration of the current
resonant power supply is a half-bridge converter. The
switching device Q(H) and Q(L) are connected in series
with VIN. The series resonant circuit and the voltage
resonant capacitor CV are connected in parallel with Q(L).
The series resonant circuit is comprised of a resonant
inductor LR, a primary winding P of a transformer T1
and a current resonant capacitor Ci.
In the resonant transformer T1, the coupling between
primary winding and secondary winding is designed to
be poor so that the leakage inductance increases. By
using it as LR, the series resonant circuit can be down
sized. The dotted mark in T1 shows the winding polarity,
the secondary windings S1 and S2 are connected so that
the polarities are set to the same position shown in
Figure 8-3, and the winding numbers of each other are
equal.
From Equation (1), the impedance of current resonant
power supply is calculated by Equation (5). From
Equation (4), the resonant frequency, f0, is calculated by
Equation (6).
where, ω is angular frequency and ω = 2πf.
(5)
(2)
(6)
When the frequency, f, changes, the impedance of
resonant circuit will change as shown in Figure 8-2
Inductance area
Impedance
Capacitance area
where,
R: the equivalent resistance of load
LR: the inductance of the resonant inductor
LP: the inductance of the primary winding P
Ci: the capacitance of current resonant capacitor
ID(H)
R
Q(H)
f0
Frequency
Series resonant circuit
VDS(H)
VGH
LR
T1
IS1
VIN
ID(L)
Figure 8-2 Impedance of resonant circuit
Q(L)
Cv
P
VOUT
(+)
S1
LP
In Equation (2), Ż becomes minimum value (= R) at
2πfL = 1/2πfC, and then ω is calculated by Equation
(3) .
VGL
VDS(L)
VCi
ICi
(3)
S2
Ci
(−)
IS2
Figure 8-3 Current resonant power supply circuit
SSC3S921 - DSJ Rev.1.5
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Apr. 01, 2016
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SSC3S921
In the current resonant power supply, Q(H) and Q(L) are
alternatively turned on and off. The on time and off time
of them are equal. There is a dead time between Q(H) on
period and Q(L) on period. During the dead time, both
Q(H) and Q(L) are in off status.
The current resonant power supply is controlled by
the frequency control. When the output voltage
decreases, the IC makes the switching frequency low so
that the output power is increased and the output voltage
is kept constant. This control must operate in the
inductance area (fSW > f0). Since the winding current is
delayed from the winding voltage in the inductance area,
the turn-on operation is ZCS (Zero Current Switching)
and the turn-off operation is ZVS (Zero Voltage
Switching). Thus, the switching loss of Q(H) and Q(L) is
nearly zero,
In the capacitance area (fSW < f0), the current resonant
power supply operates as follows. When the output
voltage decreases, the switching frequency is decreased,
and then the output power is more decreased. Thus, the
output voltage cannot be kept constant. Since the
winding current goes ahead of the winding voltage in the
capacitance area, the operation with hard switching
occurs in Q(H) and Q(L). Thus, the power loss increases.
This operation in the capacitance area is called the
capacitive mode operation. The current resonant power
supply must be operated without the capacitive mode
operation (refer to Section 8.12 about details of it).
Figure 8-4 shows the basic operation waveform of
current resonant power supply (see Figure 8-3 about the
symbol in Figure 8-4). The current resonant waveforms
in normal operation are divided a period A to a period F.
The current resonant power supply operates in the each
period as follows.
In following description,
ID(H) is the current of Q(H),
ID(L) is the current of Q(L),
VF(H) is the forwerd voltage of Q(H),
VF(L) is the forwerd voltage of Q(L),
IL is the current of LR,
VIN is an input voltage,
VCi is Ci voltage, and
VCV is CV voltage.
1) Period A
When Q(H) is ON, energy is stored into the series
resonant circuit by ID(H) flowing through the resonant
circuit and the transformer as shown in Figure 8-5. At
the same time, the energy is transferred to the
secondary circuit. When the primary winding voltage
can not keep the secondary rectifier ON, the energy to
the secondary circuit is stopped.
2) Period B
After the secondary side current becomes zero, the
resonant current flows to the primary side only as
shown in Figure 8-6 and Ci is charged by it.
VGH
VGL
VDS(H)
VIN+VF(H)
ID(H)
VDS(L)
ID(L)
ICi
VCi
VIN
IS1
IS2
A
B
D
E
C
F
Figure 8-4 The basic operation waveforms of current
resonant power supply
Q(H)
ID(H)
ON
LR
LP
VIN
S1
Q(L)
IS1
Cv
VCV
OFF
S2
Ci
VCi
Figure 8-5 Operation in period A
Q(H)
ID(H)
ON
LR
LP
VIN
S1
Q(L)
Cv
OFF
S2
Ci
Figure 8-6 Operation in period B
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3) Period C
Pireod C is the dead-time. Both Q(H) and Q(L) are in
off-state.
When Q(H) turns off, IL is flowed by the energy stored
in the series resonant circuit as shown in Figure 8-7,
and CV is discharged. When VCV decreases to VF(L),
−ID(L) flows through the body diode of Q(L) and VCV is
clamped to VF(L).
After that, Q(L) turns on. Since VDS(L) is nearly zero at
the point, Q(L) operates in ZVS and ZCS. Thus,
switching loss is nearly zero.
Q(H)
LR
OFF
LP
VIN
IL
Q(L)
Cv
VCV
OFF
-ID(L)
Ci
Figure 8-7 Operation in period C
4) Period D
When Q(L) turns on, ID(L) flows as shown in Figure 8-8
and the primary winding voltage of the transformer
adds VCi. At the same time, energy is transferred to
the secondary circuit. When the primary winding
voltage can not keep the secondary rectifier ON, the
energy to the secondary circuit is stopped.
Q(H)
LR
OFF
LP
VIN
ID(L)
Q(L)
S1
Cv
ON
5) Period E
After the secondary side current becomes zero, the
resonant current flows to the primary side only as
shown in Figure 8-9 and Ci is charged by it.
S2
IS2
Ci
VCi
Figure 8-8 Operation in period D
6) Period F
This pireod is the dead-time. Both Q(H) and Q(L) are in
off-state.
When Q(L) turns off, − IL is flowed by the energy
stored in the series resonant circuit as shown in Figure
8-10. CV is discharged. When VCV decreases to VIN +
VF(H), − ID(H) flows through body diode of Q(H) and
VCV is clamped to VIN + VF(H).
After that, Q(H) turns on. Since VDS(H) is nearly zero at
the point, Q(H) operates in ZVS and ZCS. Thus, the
switching loss is nearly zero.
Q(H)
LR
OFF
LP
VIN
ID(L)
Q(L)
S1
Cv
ON
S2
Ci
Figure 8-9 Operation in period E
7) After the Period F
Then, ID(H) flows and the operation returns to the
period A.
Q(H)
The above operation is repeated, the energy is
transferred to the secondary side from the resonant
circuit.
-ID(H)
LR
OFF
LP
VIN
-IL
Q(L)
VCV
OFF
Cv
Ci
Figure 8-10 Operation in period F
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8.2
Startup Operation
8.3
Figure 8-11 shows the VCC pin peripheral circuit.
When the following all conditions are fulfilled, the IC
starts the startup operation:
● The mains input voltage is provided, and the VSEN
pin voltage increases to the on-threshold voltage,
VSEN(ON) = 1.300 V, or more.
● The startup current, ICC(ST), which is a constant current
of 6.0 mA, is provided from the IC to capacitor C2
connected to the VCC pin, C2 is charged, and the
VCC pin voltage increases to the operation start
voltage, VCC(ON) = 17.0 V, or more.
● The FB pin voltage increases to the oscillation start
threshold voltage, VFB(ON) = 0.30 V, or more.
After that, the startup circuit stops automatically, in
order to eliminate its own power consumption.
During the IC operation, the rectified voltage from the
auxiliary winding voltage, VD, of Figure 8-11 is a power
source to the VCC pin.
The winding turns of the winding D should be
adjusted so that the VCC pin voltage is applied to
equation (7) within the specification of the mains input
voltage range and output load range of the power supply.
The target voltage of the winding D is about 19 V.
Undervoltage Lockout (UVLO)
Figure 8-12 shows the relationship of VCC and ICC.
After the IC starts operation, when the VCC pin
voltage decreases to VCC(OFF) = 8.9 V, the IC stops
switching operation by the Undervoltage Lockout
(UVLO) Function and reverts to the state before startup
again.
ICC
Stop
Start
VCC（OFF）
VCC（ON） VCC pin
voltage
Figure 8-12 VCC versus ICC
8.4
Bias Assist Function
Figure 8-13 shows the VCC pin voltage behavior
during the startup period.
⇒9.8 (V) < VCC < 32.0 (V)
(7)
The startup time, tSTART, is determined by the value of
C2 and C6 connected to the CSS pin. Since the startup
time for C6 is much smaller than that for C2, the startup
time is approximately given as below:
VCC pin voltage
IC startup
VCC(ON)
VCC(BIAS)
VCC(OFF)
Startup success
Target
operating
voltage
Increasing by output
voltage rising
Bias Assist period
(8)
Startup failure
where:
tSTART is the startup time in s,
VCC(INT) is the initial voltage of the VCC pin in V, and
ICC(ST) is the startup current, 6.0 mA
18
ST
R2
C1
R3
U1
VCC
VSEN
CSS
GND
5
10
R4 R5
C6
2
R1 D1
1
C4
VD
C2
Figure 8-11 VCC pin peripheral circuit
Time
Figure 8-13 VCC pin voltage during startup period
When the conditions of Section 8.2 are fulfilled, the
IC starts operation. Thus, the circuit current, ICC,
increases, and the VCC pin voltage begins dropping. At
the same time, the auxiliary winding voltage, VD,
increases in proportion to the output voltage rise. Thus,
the VCC pin voltage is set by the balance between
dropping due to the increase of ICC and rising due to the
increase of the auxiliary winding voltage, VD.
When the VCC pin voltage decreases to
VCC(OFF) = 8.9 V, the IC stops switching operation and a
startup failure occurs.
In order to prevent this, when the VCC pin voltage
decreases to the startup current threshold biasing voltage,
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VCC(BIAS) = 9.8 V, the Bias Assist Function is activated.
While the Bias Assist Function is activated, any
decrease of the VCC pin voltage is counteracted by
providing the startup current, ICC(ST), from the startup
circuit.
It is necessary to check the startup process based on
actual operation in the application, and adjust the VCC
pin voltage, so that the startup failure does not occur.
If VCC pin voltage decreases to VCC(BIAS) and the Bias
Assist Function is activated, the power loss increases.
Thus, VCC pin voltage in normal operation should be
set more than VCC(BIAS) by the following adjustments.
● The turns ratio of the auxiliary winding to the
secondary-side winding is increased.
● The value of C2 in Figure 8-11 is increased and/or the
value of R1 is reduced.
During all protection operation, the Bias Assist
Function is disabled.
8.5
Soft Start Function
Figure 8-14
waveforms.
CSS pin
voltage
shows
the
Soft-start
operation
Frequency control
by feedback signal
OCP operation
peropd
operated with an oscillation frequency controlled by
feedback.
When the IC becomes any of the following conditions,
C6 is discharged by the CSS Pin Reset Current,
ICSS(R) = 1.8 mA.
● The VCC pin voltage decreases to the operation stop
voltage, VCC(OFF) = 8.9 V, or less.
● The VSEN pin voltage decreases to the off-threshold
voltage, VSEN(OFF) = 1.100 V, or less.
● Any of protection operations in protection mode
(OVP, OLP or TSD) is activated.
8.6
Minimum and Maximum Switching
Frequency Setting
The minimum switching frequency is adjustable by
the value of R5 (RCSS) connected to the CSS pin. The
relationship of R5 (RCSS) and the externally adjusted
minimum frequency, f(MIN)ADJ, is shown in Figure 8-15.
The f(MIN)ADJ should be adjusted to more than the
resonant frequency, fO, under the condition of the
minimum mains input voltage and the maximum output
power.
The maximum switching frequency, fMAX, is
determined by the inductance and the capacitance of the
resonant circuit. The fMAX should be adjusted to less than
the maximum frequency, f(MAX) = 300 kHz.
SSC3S921_R2
Soft-start
period
80
C6 is charged by ICSS(C)
Time
Primary-side
winding current
OCP limit
0
Time
f(MIN)ADJ (kHz)
0
70
60
50
40
Figure 8-14 Soft-start operation
The IC has Soft Start Function to reduce stress of
peripheral component and prevent the capacitive mode
operation.
During the soft start operation, C6 connected to the
CSS pin is charged by the CSS Pin Charge Current,
ICSS(C) = − 105 μA. The oscillation frequency is varied by
the CSS pin voltage. The switching frequency gradually
decreases from f(MAX)SS* = 500 kHz at most, according
to the CSS pin voltage rise. At same time, output power
increases. When the output voltage increases, the IC is
20
30
40
50
60
RCSS (kΩ)
70
80
Figure 8-15 R5 (RCSS) versus f(MIN)ADJ
* The maximum frequency during normal operation is
f(MAX) = 300 kHz.
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8.7
High-side Driver
Figure 8-16 shows a bootstrap circuit. The bootstrap
circuit is for driving to Q(H) and is made by D3, R12 and
C12 between the REG pin and the VS pin.
When Q(H) is OFF state and Q(L) is ON state, the VS
pin voltage becomes about ground level and C12 is
charged from the REG pin.
When the voltage of between the VB pin and the VS
pin, VB-S, increases to VBUV(ON) = 6.8 V or more, an
internal high-side drive circuit starts operation. When
VB-S decreases to VBUV(OFF) = 6.4 V or less, its drive
circuit stops operation. In case the both ends of C12 and
D4 are short, the IC is protected by VBUV(OFF). D4 for
protection against negative voltage of the VS pin
VGH
VS
16
Q(H)
T1
15
C12
D4
VB 14
U1
REG
VGL
GND
Cv
R12
12
D3
Q(L)
11
10
Ci
C11
Bootstrap circuit
● D4
D4 should be a Schottky diode of low forward voltage,
VF, so that the voltage between the VB pin and the VS
pin must not decrease to the absolute maximum
ratings of −0.3 V or less.
8.8
Constant Voltage Control Operation
Figure 8-17 shows the FB pin peripheral circuit. The
FB pin is sunk the feedback current by the photo-coupler,
PC1, connected to FB pin. As a result, since the
oscillation frequency is controlled by the FB pin, the
output voltage is controlled to constant voltage (in
inductance area).
The feedback current increases under slight load
condition, and thus the FB pin voltage decreases. While
the FB pin voltage decreases to the oscillation stop
threshold voltage, VFB(OFF) = 0.20 V, or less, the IC stops
switching operation. This operation reduces switching
loss, and prevents the increasing of the secondary output
voltage. In Figure 8-17, R8 and C9 are for phase
compensation adjustment, and C5 is for high frequency
noise rejection.
The secondary-side circuit should be designed so that
the collector current of PC1 is more than 195 μA which
is the absolute value of the maximum source current,
IFB(MAX). Especially the current transfer ratio, CTR, of
the photo coupler should be taken aging degradation into
consideration.
U1
Figure 8-16 Bootstrap circuit
● D3
D3 should be an ultrafast recovery diode of short
recovery time and low reverse current. As for
Sanken’s diode lineup, AG01A (VRM = 600 V) of
UFRD series is recommended for the specification
that the maximum mains input voltage is 265VAC.
FB
3
C5
GND
10
R8
C9
PC1
Figure 8-17 FB pin peripheral circuit
● C11, C12, and R12
The values of C11, C12, and R12 are determined by
total gate charge, Qg, of external MOSFET and
voltage dip amount between the VB pin and the VS
pin in the burst mode of the standby mode change.
C11, C12, and R12 should be adjusted so that the
voltage between the VB pin and the VS is more than
VBUV(ON) = 6.8 V by measuring the voltage with a
high-voltage differential probe.
The reference value of C11 is 0.47μF to 1 μF.
The time constant of C12 and R12 should be less than
500 ns. The values of C12 and R22 are 0.047μF to 0.1
μF, and 2.2 Ω to 10 Ω.
C11 and C12 should be a film type or ceramic
capacitor of low ESR and low leakage current.
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SSC3S921
8.9
Standby Function
Standby
The IC has the Standby Function in order to increase
circuit efficiency in light load. When the Standby
Function is activated, the IC operates in the burst
oscillation mode as shown in Figure 8-18.
H
0
SB pin voltage
H
L
Standby operation
Discharging
by ISB(SNK)
VSB(OFF)
Primary-side main
winding current
Switching period
Non-switching period
VSB(STB)
0
FB pin voltage
VFB(OFF)
0
Primary-side
main winding
current
Soft-on
Time
Soft-off
0
Switching stop
Figure 8-18 Standby waveform
Time
Figure 8-20 Standby change operation waveforms
The burst oscillation has periodic non-switching
intervals. Thus, the burst mode reduces switching losses.
Generally, to improve efficiency under light load
conditions, the frequency of the burst mode becomes
just a few kilohertz. In addition, the IC has the Soft-on
and the Soft-off Function in order to suppress rapid and
sharp fluctuation of the drain current during the burst
mode. thus, the audible noises can be reduced (refer to
Section 8.9.2). The operation of the IC changes to the
standby operation by the external signal (refer to Section
8.9.1).
8.9.1 Standby Mode Changed by External
Signal
Figure 8-19 shows the standby mode change circuit
with external signal. Figure 8-20 shows the standby
change operation waveforms.
REG
12
C11
U1
FB
SB
3 R8
9
R58
R16
Q1
R15
PC2
R17
C5
C10
Standby
Q51
R59
C9
PC1
PC2
GND
Figure 8-19 Standby mode change circuit
When the standby terminal of Figure 8-19 is provided
with the L signal, Q1 turns off, C10 connected to the SB
pin is discharged by the sink current, ISB(SNK) = 10 µA,
and the SB pin voltage decreases. When the SB pin
voltage decrease to the SB Pin Oscillation Stop
Threshold Voltage, VSB(OFF) = 0.5 V, the operation of the
IC is changed to the standby mode. When SB pin
voltage is VSB(OFF) = 0.5 V or less and FB pin voltage is
Oscillation Stop Threshold Voltage VFB(OFF) = 0.20 V or
less, the IC stops switching operation. When the standby
terminal is provided with the H signal and the SB pin
voltage increases to Standby Threshold Voltage
VSB(STB) = 5.0 V or more, the IC returns to normal
operation.
8.9.2 Burst Oscillation Operation
In standby operation, the IC operates burst oscillation
where the peak drain current is suppressed by Soft-On
/Soft-off Function in order to reduce audible noise from
transformer. During burst oscillation operation, the
switching oscillation is controlled by SB pin voltage.
Figure 8-21 shows the burst oscillation operation
waveforms.
When the SB pin voltage decreases to VSB(OFF) = 0.5 V
or less and the FB pin voltage decreases to
VFB(OFF) = 0.20 V or less, the IC stops switching
operation and the output voltage decreases. Since the
output voltage decreases, the FB pin voltage increases.
When the FB pin voltage increases to the oscillation
start threshold voltage, VFB(ON) = 0.30 V, C10 is charged
by ISB(SRC) = − 10 µA, and the SB pin voltage gradually
increases. When the SB pin voltage increases to the
oscillation start threshold voltage, VSB(ON) = 0.6 V, the
IC resumes switching operation, controlling the
frequency control by the SB pin voltage. Thus, the
output voltage increases (Soft-on). After that, when FB
pin voltage decrease to oscillation stop threshold voltage,
VFB(OFF) = 0.20 V, C10 is discharged by ISB(SNK) = 10 µA
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and SB pin voltage decreases. When the SB pin voltage
decreases to VSB(OFF) again, the IC stops switching
operation. Thus, the output voltage decreases (Soft-off).
The SB pin discharge time in the Soft-on and Soft-off
Function depends on C10. When the value of C10
increases, the Soft-On/Soft-off Function makes the peak
drain current suppressed, and makes the burst period
longer. Thus, the output ripple voltage may increase
and/or the VCC pin voltage may decrease. If the VCC
pin voltage decreases to VCC(BIAS) = 9.8 V, the Bias
Assist Function is always activated, and it results in the
increase of power loss (refer to Section 8.4).
Thus, it is necessary to adjust the value of C10 while
checking the input power, the output ripple voltage, and
the VCC pin voltage. The reference value of C10 is
about 0.001 μF to 0.1 μF.
Standby operation
SB pin voltage
VSB(STB)
VSB(OFF)
0
ADJ pin voltage
VREG
0
Figure 8-22 PFC ON/OFF Function
PFC IC
(SSC2016S)
VCC
U1
QC
12
RADJ1
Output current
0
REG
RADJ2
GND
4 ADJ
10 GND
Output voltage
0
Figure 8-23 Typical circuit that PFC IC is stopped by the
ADJ pin signal (VCC(ON)_PFC < VREG)
FB pin voltage
VFB(ON)
VFB(OFF)
0
Charged
by ISB(SRC)
SB pin voltage
8.10 Automatic Dead Time Adjustment
Function
Discharged
by ISB(SNK)
VSB(ON)
VSB(OFF)
0
Primary-side
main winding
current
0
Soft-on
Soft-off
Time
Figure 8-21 Burst oscillation operation waveforms
8.9.3 PFC ON/OFF Function
Figure 8-22 shows the operational waveform of PFC
ON/OFF Output Function. When output power
decreases and SB pin voltage reaches to V SB(OFF) = 0.5 V,
the PFC ON/OFF Function activates and ADJ pin
voltage increases to ADJ Pin Voltage in Standby
Operation, VADJ(H) = VREG = 10.0 V. When output power
increases and SB pin voltage reaches to VSB(STB) = 5.0 V,
the ADJ pin voltage decreases to ADJ Pin Voltage in
Normal Operation, VADJ(L) = 1 V.
Using the signal, the power supply of PFC control IC
can be turned on/off when the IC becomes standby
operation. When the operation starting voltage of PFC
IC, VCC(ON)_PFC, is less than VREG, the PFC circuit on/off
system can be realized by low component count as
shown in Figure 8-23. SSC2016S that is Sanken PFC
control IC is recommended.
The dead time is the period when both the high-side
and the low-side power MOSFETs are off.
As shown in Figure 8-24, if the dead time is shorter
than the voltage resonant period, the power MOSFET is
turned on and off during the voltage resonant operation.
In this case, the power MOSFET turned on and off in
hard switching operation, and the switching loss
increases. The Automatic Dead Time Adjustment
Function is the function that the ZVS (Zero Voltage
Switching) operation of Q(H) and Q(L) is controlled
automatically by the voltage resonant period detection of
IC. The voltage resonant period is varied by the power
supply specifications (input voltage and output power,
etc.). However, the power supply with this function is
unnecessary to adjust the dead time for each power
supply specification.
As shown in Figure 8-25, the VS pin detects the dv/dt
period of rising and falling of the voltage between drain
and source of the low-side power MOSFET, VDS(L), and
the IC sets its dead time to that period. This function
controls so that the high-side and the low-side power
MOSFETs are automatically switched to Zero Voltage
Switching (ZVS) operation. This function operates in the
period from td(MIN) = 0.24 µs to td(MAX) = 1.65 µs.
In minimum output power at maximum input voltage
and maximum output power at minimum input voltage,
the ZCS (Zero Current Switching) operation of IC (the
drain current flows through the body diode is about 600
ns as shown in Figure 8-26), should be checked based on
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SSC3S921
actual operation in the application.
VAC
VGL
R2
VDC
VGH
Dead time
C1
U1
R3
1
Q(H) D-S voltage,
VDS(H)
Loss increase by hard
switching operation
VSEN
R4
10
GND
C4
Figure 8-27 VSEN pin peripheral circuit
Voltage resonant period
Figure 8-24 ZVS failure operation waveform
U1
VGH
RV
DETECTOR
VS 15
VGL
Main
T1
16
Given, the DC input voltage when the IC starts as
VIN(ON), the DC input voltage when the switching
operation of the IC stops as VIN(OFF). VIN(ON) is calculated
by Equation (9). VIN(OFF) is calculated by Equation (10).
Thus, the relationship between VIN(ON) and VIN(OFF) is
Equation (11).
VDS(L)
Cv
11
(9)
GND
10
Ci
(10)
Low-side, VDS(L) On
dv Off
dt
dt
On
Dead time period
(11)
Figure 8-25 VS pin and dead time period
The detection resistance is calculated from Equation
(9) as follows:
Q(H) drain current,
ID(H)
(12)
Flows through body
diode about 600 ns
Figure 8-26 ZCS check point
8.11 Brown-In and Brown-Out Function
Figure 8-27 shows the VSEN pin peripheral circuit.
This function detects the mains input voltage, and stops
switching operation during low mains input voltage, to
prevent exceeding input current and overheating.
R2 to R4 set the detection voltage of this function.
When the VCC pin voltage is higher than VCC(ON), this
function operates depending on the VSEN pin voltage as
follows:
Because R2 and R3 are applied high DC voltage and
are high resistance, the following should be considered:
● Select a resistor designed against electromigration
according to the requirement of the application, or
● Use a combination of resistors in series for that to
reduce each applied voltage
The reference value of R2 is about 10 MΩ.
C4 shown in Figure 8-27 is for reducing ripple
voltage of detection voltage and making delay time. The
value is 0.1 µF or more, and the reference value is about
0.47 µF.
The value of R2, R3 and R4 and C4 should be
selected based on actual operation in the application.
● When the VSEN pin voltage is more than V SEN
(ON) = 1.300 V, the IC starts.
● When the VSEN pin voltage is less than VSEN
(OFF) = 1.100 V, the IC stops switching operation.
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SSC3S921
The resonant power supply is operated in the
inductance area shown in Figure 8-28. In the capacitance
area, the power supply becomes the capacitive mode
operation (refer to Section 8.1). In order to prevent the
operation, the minimum oscillation frequency is needed
to be set higher than f0 on each power supply
specification. However, the IC has the capacitive mode
operation Detection Function kept the frequency higher
than f0. Thus, the minimum oscillation frequency setting
is unnecessary and the power supply design is easier. In
addition, the ability of transformer is improved because
the operating frequency can operate close to the resonant
frequency, f0.
The resonant current is detected by the RC pin, and
the IC prevents the capacitive mode operation. When the
capacitive mode is detected, the C7 connected to CL pin
is charged by ICL(SRC) = − 17 μA. When the CL pin
voltage increases to VCL(OLP), the OLP is activated and
the switching operation stops. During the OLP operation,
the intermittent operation by UVLO is repeated (refer to
Section 8.18). The detection voltage is changed to
VRC1 = ±0.10 V or VRC2 = ±0.50 V depending on the load
as shown in Figure 8-30 and Figure 8-31.
The Capacitive Mode Operation Detection Function
operations as follows:
● Period in which the Q(H) is ON
Figure 8-29 shows the RC pin waveform in the
inductance area, and Figure 8-30 and Figure 8-31
shows the RC pin waveform in the capacitance area.
In the inductance area, the RC pin voltage doesn’t
cross the plus side detection voltage in the downward
direction during the on period of Q(H) as shown in
Figure 8-29. On the contrary, in the capacitance area,
the RC pin voltage crosses the plus side detection
voltage in the downward direction. At this point, the
capacitive mode operation is detected. Thus, Q(H) is
turned off, and Q(L) is turned on, as shown in Figure
8-30 and Figure 8-31.
● Period in which the Q(L) is on
Contrary to the above of Q(H), in the capacitance area,
the RC pin voltage crosses the minus side detection
voltage in the upward directiont during the on period
of Q(L) At this point, the capacitive mode operation is
detected. Thus, Q(L) is turned off and Q(H) is turned on.
As above, since the capacitive mode operation is
detected by pulse-by-pulse and the operating frequency
is synchronized with the frequency of the capacitive
mode operation, and the capacitive mode operation is
prevented. In addition to the adjusting method of ROCP,
C3, and R6 in Section 1.1, ROCP, C3, and R6 should be
adjusted so that the absolute value of the RC pin voltage
increases to more than |VRC2| = 0.50 V under the
condition caused the capacitive mode operation easily,
such as startup, turning off the mains input voltage, or
output shorted. The RC pin voltage must be within the
absolute maximum ratings of −6 to 6 V
Capacitance area
Inductance area
Impedance
8.12 Capacitive Mode Detection Function
Operating area
f0
Resonant fresuency
Hard switching
Sift switching
Uncontrollable operation
Figure 8-28 Operating area of resonant power supply
VDS(H)
OFF
ON
RC pin
voltage
+VRC
0
Figure 8-29 RC pin voltage in inductance area
VDS(H)
0
OFF
ON
Capacitive mode
operation detection
RC pin
voltage +VRC2
+VRC1
0
Figure 8-30 High side capacitive mode detection in light
load
VDS(H)
0
RC pin
voltage +VRC2
+VRC1
0
OFF
ON
Capacitive mode
operation detection
Figure 8-31 High side capacitive mode detection in
heavy load
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SSC3S921
8.13 Input Electrolytic Capacitor
Discharge Function
8.14 Reset Detection Function
Figure 8-32 shows an application that residual voltage
of the input capacitor, C1, is reduced after turning off
the mains input voltage. R2 is connected to the AC input
lines through D7 and D8. Just after turning off the mains
input voltage, the VSEN pin voltage decreases to
VSEN(OFF) = 1.100 V according to a short time of the time
constant with R2 to R4 and C4, and C1 is discharged by
the equivalent to ICC(ST) = 6.0 mA.
D7
Main input →off
D8
6 mA
(ICC(ST))
C1
R2
18
ST
R3
C4
U1
VSEN
1
GND
10
R4
Figure 8-32 Input capacitor discharge
The magnetizing current means the circulating current
applied for resonant operation, and that flows only into
the primary-side circuit. During the startup period when
the feedback control for the output voltage is inactive, if
the magnetizing current cannot be reset in the on-period
because of unbalanced operation, negative current may
flows just before a power MOSFET turns off, and hard
switching may occur, and stresses of power MOSFET
may increase. To prevent this hard switching, the IC
incorporates the Reset Detection Function.
Figure 8-34 shows the high-side operation and drain
current waveform examples in normal resonant
operation and reset failure operation. The Reset
Detection Function extends the on-period until the
absolute value of RC pin voltage, |VRC1|, increases to
0.10 V or more. Thus, this function prevents the hard
switching operation. When the on-period reaches the
maximum reset time, tRST(MAX) = 5 μs, the on-period
expires at that moment, and the power MOSFET turns
off (refer to Figure 8-33).
VGH pin
voltage Low
High
VGL pin High
voltage
Low
Turning-on
in negative drain current
ID(H)
Reset failure waveform
VRC= +0.1V
0
Expanded
on-period
Normal on-period
tRST(MAX)
Figure 8-33 Reset detection operation example
at high-side on-period
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○ Normal resonant operation
B
ID(H)
C
● Reset failure operation
ID(H)
Magnetizing
current
Point D
VDS(H)=0V
A
Point A
VDS(H)=0V
Q(H)
Lr
Q(L)
Lr
Q(L)
ID(H)
Off
Ci
Lp
ID(H)
Cv
Ci
Point E
VDS(H)=0V
Q(H)
Q(H)
Lr
On
Q(L)
Q(L)
ID(H)
Off
Ci
Q(H)
Off
Lp
Q(L)
Lp
ID(H)
Cv
Ci
Point F
Q(H)
Lr
Lr
On
Lp
Cv
Point C
Off
E
D
Off
Lp
Cv
Point B
VDS(H)=0V
Off
0
Q(H)
Off
Off
F
Recovery current
of body diode
ID(H)
Off
Lr
Lp
Q(L)
Cv
Ci
Turning on at VDS(L)= 0V results in　soft-switching
On
Cv
Ci
Turning on at VDS(L) >> 0V results in hard-switching
Figure 8-34 High-side operation and drain current waveform examples in normal resonant operation
and in reset failure operation
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SSC3S921
8.15 Overvoltage Protection (OVP)
When the voltage between the VCC pin and the GND
pin is applied to the OVP threshold voltage,
VCC(OVP) = 32.0 V, or more, the Overvoltage Protection
(OVP) is activated, and the IC stops switching operation
in protection mode. After stopping, the VCC pin voltage
decreases to VCC(OFF) = 8.9 V, the Undervoltage Lockout
(UVLO) Function is activated, and the IC reverts to the
state before startup again.
After that, the startup circuit is activated, the VCC pin
voltage increases to VCC(ON) = 17.0 V, and the IC restarts.
During the protection mode, restart and stop are repeated.
When the fault condition is removed, the IC returns to
normal operation automatically. When the auxiliary
winding supplies the VCC pin voltage, the OVP is able
to detect an excessive output voltage, such as when the
detection circuit for output control is open in the
secondary-side circuit because the VCC pin voltage is
proportional to the output voltage.
The output voltage of the secondary-side circuit at
OVP operation, VOUT(OVP), is approximately given as
below:
and C6 should be adjusted based on actual operation in
the application. The following is a reference adjusting
method of ROCP, C3, R6, and C8:
● C3 and ROCP
C3 is 100pF to 330pF (around 1 % of Ci value).
ROCP is around 100 Ω.
Given the current of the high side power MOSFET at
ON state as ID(H). ROCP is calculated Equation (14).
The detection voltage of ROCP is used the detection of
the capacitive mode operation (refer to Section 8.12).
Therefore, setting of ROCP and C3 should be taken
account of both OCP and the capacitive mode
operation.
(14)
● R6 and C8 are for high frequency noise reduction.
R6 is 100 Ω to 470 Ω. C6 is 100 pF to 1000 pF.
Q(H)
VGH
(13)
VS
U1
where,
VOUT(NORMAL) : Output voltage in normal operation
VCC(NORMAL): VCC pin voltage in normal operation
8.16 REG Overvoltage Protection
(REG_OVP)
The IC has REG Overvoltage Protection (REG_OVP)
for the overvoltage of the REG pin.
When the REG pin voltage increases to REG Pin
OVP Threshold Voltage, VREG(OVP) = 12.4 V, the
REG_OVP is activated and the IC stops switching
operation at latched state. Releasing the latched state is
done by dropping the VCC pin voltage below REG Pin
Overvoltage Protection Release Threshold Voltage,
VCC(L.OFF) = 5.0 V.
8.17 Overcurrent Protection (OCP)
The Overcurrent Protection (OCP) detects the drain
current, ID, on pulse-by-pulse basis, and limits output
power. In Figure 8-35, this circuit enables the value of
C3 for shunt capacitor to be smaller than the value of Ci
for current resonant capacitor, and the detection current
through C3 is small. Thus, the loss of the detection
resistor, ROCP, is reduced, and ROCP is a small-sized one
available. There is no convenient method to calculate the
accurate resonant current value according to the mains
input and output conditions, and others. Thus, ROCP, C3,
T1
15
Q(L)
VGL
CSS RC
5 7
16
11
10
PL GND
8 R7
Cv
I(H)
Ci
C3
R6
R5
C6 C8 ROCP
Figure 8-35 RC pin peripheral circuit
The OCP operation has two-step threshold voltage as
follows:
Step I, RC pin threshold voltage (Low), VRC(L):
This step is active first. When the absolute value of
the RC pin voltage increases to more than |VOC(L) | = 1.50
V, C6 connected to the CSS pin is discharged by
ICSS(L) = 1.8 mA. Thus, the switching frequency increases,
and the output power is limited. During discharging C6,
when the absolute value of the RC pin voltage decreases
to |VRC(L)| or less, the discharge stops.
Step II, RC pin threshold voltage (High-speed),
VRC(S):
This step is active second. When the absolute value of
the RC pin voltage increases to more than |VRC(S) | = 2.30
V, the high-speed OCP is activated, and power
MOSFETs reverse on and off. At the same time, C6 is
discharged by ICSS(S) = 20.5 mA. Thus, the switching
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SSC3S921
frequency quickly increases, and the output power is
quickly limited. This step operates as protections for
exceeding overcurrent, such as the output shorted.
When the absolute value of the RC pin voltage
decreases to |VRC(S)| or less, the operation is changed to
the above Step I.
8.18 Overload Protection (OLP)
Figure 8-36 shows the Overload Protection (OLP)
waveforms.
When the absolute value of RC pin voltage increases
to |VRC(L)| = 1.50 V by increasing of output power, the
Overcurrent Protection (OCP) is activated. After that,
the C7 connected to CL pin is charged by ICL(SRC) = − 17
μA. When the OCP state continues and CL pin voltage
increases to VCL(OLP), the OLP is activated.
When CL pin voltage becomes the threshold voltage
of OLP, VCL(OLP) = 4.2 V, the OLP is activated and the
switching operation stops. During the OLP operation,
the intermittent operation by UVLO is repeated (refer to
Section 8.15). When the fault condition is removed, the
IC returns to normal operation automatically.
RC pin voltage
VRC(L)
voltage is proportional to the output current.
On actual operation of the application, C7 connected
to the CL pin should be adjusted so that ripple voltage
of the CL pin reduces. R7 connected to the PL pin
should be adjusted so that the OLP at the minimum
mains input voltage is activated before the OCP
limited by the low threshold voltage of OCP, VRC(L).
The PL pin voltage and the CL pin voltage must be
within the absolute maximum ratings of −0.3 to 6 V,
by adjusting R7, in the OCP operation point at the
minimum mains input voltage.
When the proportional voltage to the output current is
unused, the PL pin should be pulled down by the
resistance of about 47 kΩ connected between PL pin
and GND pin.
Mains Input
Load current
U1
CL pin voltage
VCL(OLP)
Charged by ICL(SRC)
0
0
VGH/VGL
16
VS
15
R3
Q(L)
VGL
11
Cv
1 VSEN
GND 10
CL RC PL
6 7
8
R7
Ci
C3
R6
R4
C4 C7 C8 ROCP
Figure 8-37 the peripheral circuit of PL pin and CL pin
VGH pin
voltage
ROCP voltage
VCC pin voltage
VCC(ON)
VCC(P.OFF)
VGH
R2
0
VRC(L)
Magnetizing current
Output current
T1
Q(H)
C1
0V
CL pin source
current 0A
CL pin voltage
0V
Load current
Magnetizing
current
Proportional
voltage to
output current
0
Figure 8-38 The waveforms of CL pin
Figure 8-36 OLP waveform
● PL Pin and CL Pin Setup:
The primary-side winding current as shown in Figure
8-37 includes the magnetizing current not transferred
to the secondary-side circuit, and the load current
proportional to the output current.
The current separated from the primary-side winding
current by C3 flows to the PL pin. As shown in Figure
8-38, the primary-side winding current flows to the
C7 connected to CL pin during the high side power
MOSFET turning on. The magnetizing current
becomes zero by charging and discharging. Only the
load current is charged to C7. As a result, the CL pin
8.19 Thermal Shutdown (TSD)
When the junction temperature of the IC reach to the
Thermal Shutdown Temperature T j(TSD) = 140 °C (min.),
Thermal Shutdown (TSD) is activated and the IC stops
switching operation. When the VCC pin voltage is
decreased to VCC(P.OFF) = 8.9 V or less and the junction
temperature of the IC is decreased to less than Tj(TSD),
the IC restarts.
During the protection mode, restart and stop are
repeated. When the fault condition is removed, the IC
returns to normal operation automatically.
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SSC3S921
9.
9.1
Design Notes
When the gate resistances are adjusted, the gate
waveforms should be checked that the dead time is
ensured as shown in Figure 9-2.
External Components
RB
Take care to use the proper rating and proper type of
components.
DS
Drain
Gate
RA
9.1.1
Input and Output Electrolytic
Capacitors
RGS
Apply proper derating to ripple current, voltage, and
temperature rise. The electrolytic capacitor of high
ripple current and low impedance types, designed for
switch mode power supplies, is recommended to use.
9.1.2
Source
Figure 9-1 Power MOSFET peripheral circuit
High-side
Gate
Resonant Transformer
Vth(min.)
The resonant power supply uses the leakage
inductance of transformer. Therefore, in order to reduce
the effect of the eddy current and the skin effect, the
wire of transformer should be used a bundle of fine litz
wires.
Low-side
Gate
Dead time
Dead time
Vth(min.)
9.1.3
Current Detection Resistor, ROCP
Choose a type of low internal inductance because a
high frequency switching current flows to ROCP, and of
properly allowable dissipation.
9.1.4
Current Resonant Capacitor, Ci
Large resonant current flows through Ci. Ci should
use the polypropylene film capacitor with low loss and
high current capability. In addition, Ci must be
considered its frequency characteristic since high
frequency current flows.
9.1.5
Figure 9-2 Dead time confirmation
9.2
PCB Trace Layout and Component
Placement
Since the PCB circuit design and the component
layout significantly affect the power supply operation,
EMI noise, and power dissipation, the high frequency
trace of PCB shown in Figure 9-3 should be designed
low impedance by small loop and wide trace.
Gate Pin Peripheral Circuit
The VGH pin and the VGL pin are gate drive output
pins for external power MOSFETs.
The peak source current of both of them is – 540 mA,
and the peak sink current is 1.50 A.
DS of Figure 9-1 makes a turn-off speed faster.
RA, RB and Ds should be adjusted considering power
losses of power MOSFETs, gate waveforms (reduction
of ringing caused by pattern layout and others), and EMI
noise.
RA is about 33 Ω to 330 Ω. RB is about 10 Ω.
RGS prevents malfunctions caused by steep dv/dt at
turning off power MOSFET. RGS is recommended to be
a resistor of 10 k to 100 kΩ close to the Gate and the
Source of power MOSFET.
Figure 9-3 High frequency current loops (hatched areas)
In addition, the PCB circuit design should be taken
account as follows:
Figure 9-4 shows the circuit design example.
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SSC3S921
1) Main Circuit Trace Layout
This is the main trace containing switching currents,
and thus it should be as wide trace and small loop as
possible.
4) Peripheral Components for the IC Control
These components should be placed close to the IC,
and be connected to the IC pin as short as possible.
5) Bootstrap Circuit Components
These components should be connected to the IC pin
as short as possible, and the loop for these should be
as small as possible.
2) Control Ground Trace Layout
When large current flows into the control ground trace,
the operation of IC might be affected by it. The
control ground trace should be separate from the main
circuit trace, and should be connected at a single point
grounding as close to the GND pin as possible.
6) Secondary side Rectifier Smoothing Circuit Trace
Layout
This is the trace of the rectifier smoothing loop,
carrying the switching current, and thus it should be as
wide trace and small loop as possible.
3) VCC Trace Layout
This is the trace for supplying power to the IC, and
thus it should be as small loop as possible. If C3 and
the IC are distant from each other, placing a film
capacitor Cf (about 0.1 μF to 1.0 μF) close to the VCC
pin and the GND pin is recommended.
(1)Main trace should
be wide and short
C1
R4
R3
R2
VSEN
VCC
R8
FB
ADJ
RADJ1 CADJ
R5
RADJ2
C6
QC
CSS
CL
C7
C8
RC
ROCP
R6
(4)Peripheral
components for IC
control should
place near IC
1
18
2
17
3
16
(6)Main trace of
secondary side should
be wide and short
ST
C4
R7
PL
SB
T1
4
5
SSC3S921
Cf
C5
C9
PC1
PFC
IC
VCC
CY
BR1
6
15
14
7
8
9
R15
VGH
R10
D53
D5
C52
Q(H)
R11
VS
VB
C12
D4
CV
R12
13
U1
VAC
12
11
10
D3
D54
REG
D6
R16
VGL
GND
Q(L)
Ci
R13
C11
(5)Boot strap trace should
be small loop
C3
R14
D1
C10
A
R1
C2
(2)GND trace for IC
should be connected
at a single point
(3)Loop of VCC and C2 should be short
Figure 9-4 Peripheral circuit trace example around the IC
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SSC3S921
10. Pattern Layout Example
The following show the PCB pattern layout example and the schematic of circuit using SSC3S921.
(5)Boot strap trace should be
small loop
(1)Main trace should be
wide and short
(6)Main trace of secondary side
should be wide and short
S3
Lp
S4
S1
S2
D
(2)GND trace for IC should be
connected at a single point
(4)Peripheral components for IC
control should placed near IC
(3)Loop of VCC and C2
should be short
Figure 10-1 PCB pattern layout example
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SSC3S921
Main1
CN1
FP101
LX101
PSA50117_Rev.2.0
LX102
CP110
DP101
RX101
CY101
CX102
BD101
VR101
LP101
RX102
1,2,3
(1,2)
RX103
6,7,8,9
(5,6,7,8)
PFC OUT
DBH282312
(DBH332514)
CY102
CX101
DP102
RP102
CX103
11
(12)
TH101
RP106
12(13,14)
RP115
Main2
CP102 CP103
DP103
RP107
QP101
QP103
CP115
CP101
RP103
RP108
RP114
QP104
RP109
RP104
RP113
CP111
RP111 RP112
ZP101
SSC2016S
RP101
RP105
5 ZCD
CS 4
6 GND
COMP 3
7 OUT
CT 2
8 VCC
FB 1
PFC Vcc
QP102
STBY
ON/OFF
RP116
CP104
CP106
CP105
CP112 CP113
CP109
RP110
CP114
CP108
CP107
RP117
DM210
Main1
DM211
Main2
RM201
PFC OUT
T1
RM205
RM204
RM203
RM202
DM303
ZM201
SSC3S921
CM201
CN602
(15, 16)
12
18Vout
QM201
PFC
ON/OFF
VSEN
2
VCC
ST
18
CM214
RM212
CM202
VGH
3
FB
4
ADJ
VS 15
CM203
5
CSS
VB 14
CM204
6
CL
CM205
7
16
RM214
1
RM213
1
(1,2)
DM202
RM210 RM209
DM203
CM210
8
RC
PL
QM202
RM309
CM215
VGL
RM310
RM215
(3,4)
2,3
11
GND
S1
10
DM301
12.8Vout
RM301
PC201
S2
RM225
RM222
CM207
CM211
CM216 CM217
QM204
RM224
CM208
RM319
RM306
9 (12)
CM213
RM206
Jumper
QM203
DM206
5
(7,8)
RM302
6,7
(9,10)
RM316
QM301
RM208
PC202
CM209
DM208
RM322
CM304
RM311
D
(5,6)
4
DBS3360
(TBS4016)
RM317
RM314
RM303 CM305
DM305
RM308
QM303
PC202
RM315
QM302
PC201
POWER
_ON
ZM301
RM219
CM206
CN603
RM313
RM312
RM318
RM220
RM320
RM307
DM302
RM207 DM207
PFC Vcc
CN601
CM303
RM217
C212
RM221
CM301CM307
(11)
8
DM205
SB
RM321
CM306
DM204
REG 12
RM223
9
CM302
11
(14)
Lp
RM218
RM216
RM211
S3
10 (13)
S4
DM304
CM310
RM305
RM304
DM209
CY203
Fault signal_1
Fault signal_2
Figure 10-2 PCB pattern layout example circuit
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SSC3S921
IMPORTANT NOTES
● All data, illustrations, graphs, tables and any other information included in this document as to Sanken’s products listed herein (the
“Sanken Products”) are current as of the date this document is issued. All contents in this document are subject to any change
without notice due to improvement of the Sanken Products, etc. Please make sure to confirm with a Sanken sales representative
that the contents set forth in this document reflect the latest revisions before use.
● The Sanken Products are intended for use as components of general purpose electronic equipment or apparatus (such as home
appliances, office equipment, telecommunication equipment, measuring equipment, etc.). Prior to use of the Sanken Products,
please put your signature, or affix your name and seal, on the specification documents of the Sanken Products and return them to
Sanken. When considering use of the Sanken Products for any applications that require higher reliability (such as transportation
equipment and its control systems, traffic signal control systems or equipment, disaster/crime alarm systems, various safety
devices, etc.), you must contact a Sanken sales representative to discuss the suitability of such use and put your signature, or affix
your name and seal, on the specification documents of the Sanken Products and return them to Sanken, prior to the use of the
Sanken Products. The Sanken Products are not intended for use in any applications that require extremely high reliability such as:
aerospace equipment; nuclear power control systems; and medical equipment or systems, whose failure or malfunction may result
in death or serious injury to people, i.e., medical devices in Class III or a higher class as defined by relevant laws of Japan
(collectively, the “Specific Applications”). Sanken assumes no liability or responsibility whatsoever for any and all damages and
losses that may be suffered by you, users or any third party, resulting from the use of the Sanken Products in the Specific
Applications or in manner not in compliance with the instructions set forth herein.
● In the event of using the Sanken Products by either (i) combining other products or materials therewith or (ii) physically,
chemically or otherwise processing or treating the same, you must duly consider all possible risks that may result from all such
uses in advance and proceed therewith at your own responsibility.
● Although Sanken is making efforts to enhance the quality and reliability of its products, it is impossible to completely avoid the
occurrence of any failure or defect in semiconductor products at a certain rate. You must take, at your own responsibility,
preventative measures including using a sufficient safety design and confirming safety of any equipment or systems in/for which
the Sanken Products are used, upon due consideration of a failure occurrence rate or derating, etc., in order not to cause any human
injury or death, fire accident or social harm which may result from any failure or malfunction of the Sanken Products. Please refer
to the relevant specification documents and Sanken’s official website in relation to derating.
● No anti-radioactive ray design has been adopted for the Sanken Products.
● No contents in this document can be transcribed or copied without Sanken’s prior written consent.
● The circuit constant, operation examples, circuit examples, pattern layout examples, design examples, recommended examples, all
information and evaluation results based thereon, etc., described in this document are presented for the sole purpose of reference of
use of the Sanken Products and Sanken assumes no responsibility whatsoever for any and all damages and losses that may be
suffered by you, users or any third party, or any possible infringement of any and all property rights including intellectual property
rights and any other rights of you, users or any third party, resulting from the foregoing.
● All technical information described in this document (the “Technical Information”) is presented for the sole purpose of reference
of use of the Sanken Products and no license, express, implied or otherwise, is granted hereby under any intellectual property
rights or any other rights of Sanken.
● Unless otherwise agreed in writing between Sanken and you, Sanken makes no warranty of any kind, whether express or implied,
including, without limitation, any warranty (i) as to the quality or performance of the Sanken Products (such as implied warranty
of merchantability, or implied warranty of fitness for a particular purpose or special environment), (ii) that any Sanken Product is
delivered free of claims of third parties by way of infringement or the like, (iii) that may arise from course of performance, course
of dealing or usage of trade, and (iv) as to any information contained in this document (including its accuracy, usefulness, or
reliability).
● In the event of using the Sanken Products, you must use the same after carefully examining all applicable environmental laws and
regulations that regulate the inclusion or use of any particular controlled substances, including, but not limited to, the EU RoHS
Directive, so as to be in strict compliance with such applicable laws and regulations.
● You must not use the Sanken Products or the Technical Information for the purpose of any military applications or use, including
but not limited to the development of weapons of mass destruction. In the event of exporting the Sanken Products or the Technical
Information, or providing them for non-residents, you must comply with all applicable export control laws and regulations in each
country including the U.S. Export Administration Regulations (EAR) and the Foreign Exchange and Foreign Trade Act of Japan,
and follow the procedures required by such applicable laws and regulations.
● Sanken assumes no responsibility for any troubles, which may occur during the transportation of the Sanken Products including
the falling thereof, out of Sanken’s distribution network.
● Although Sanken has prepared this document with its due care to pursue the accuracy thereof, Sanken does not warrant that it is
error free and Sanken assumes no liability whatsoever for any and all damages and losses which may be suffered by you resulting
from any possible errors or omissions in connection with the contents included herein.
● Please refer to the relevant specification documents in relation to particular precautions when using the Sanken Products, and refer
to our official website in relation to general instructions and directions for using the Sanken Products.
DSGN-CEZ-16001
SSC3S921 - DSJ Rev.1.5
SANKEN ELECTRIC CO.,LTD.
Apr. 01, 2016
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2015
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