str3a400 ds en

Off-Line PWM Controllers with Integrated Power MOSFET
STR3A400 Series
Data Sheet
Description
Package
The STR3A400 series are power ICs for switching
power supplies, incorporating a MOSFET and a current
mode PWM controller IC.
The low standby power is accomplished by the
automatic switching between the PWM operation in
normal operation and the burst-oscillation under light
load conditions. The product achieves high
cost-performance power supply systems with few
external components.
DIP8
Features
● Electrical Characteristics
fOSC(AVG)(typ.) = 65 kHz
VDSS(min.) = 650 V
Products
● Low Thermal Resistance Package
● Improving circuit efficiency (Since the step drive
control can keep VRM of secondary rectification
diodes low, the circuit efficiency can be improved by
low VF)
● Current Mode Type PWM Control
● Soft Start Function
● Automatic Standby Function
No Load Power Consumption < 15mW
● Operation Mode
Normal Operation ----------------------------- PWM Mode
Light Load Operation ------------------------ Green-Mode
Standby ---------------------------- Burst Oscillation Mode
● Random Switching Function
● Slope Compensation Function
● Leading Edge Blanking Function
● Bias Assist Function
● Protections
Two Types of Overcurrent Protection (OCP):
Pulse-by-Pulse, built-in compensation circuit to
minimize OCP point variation on AC input voltage
Overload Protection (OLP): Auto-restart
Overvoltage Protection (OVP): Latched shutdown or
auto-restart
Thermal Shutdown (TSD): Latched shutdown or
auto-restart with hysteresis
Typical Application
Not to Scale
Lineup
STR3A45×
OVP, TSD Operation
Latched shutdown
STR3A45×D
Auto-restart
● MOSFET ON Resistance and Output Power, P OUT*
Products
RDS(ON)
(max.)
STR3A451
POUT
(Adapter)
AC85
AC230V
~265V
POUT
(Open frame)
AC85
AC230V
~265V
4.0 Ω
29.5 W
19.5 W
37 W
23 W
1.9 Ω
37 W
27.5 W
53 W
35 W
1.1 Ω
45 W
35 W
65 W
44 W
STR3A451D
STR3A453
STR3A453D
STR3A455
STR3A455D
* The output power is actual continues power that is measured
at 50 °C ambient. The peak output power can be 120 to
140 % of the value stated here. Core size, ON Duty, and
thermal design affect the output power. It may be less than
the value stated here.
Applications
L51
BR1
D51
T1
VAC
VOUT
R1
C5
PC1
C1
P
R55
C51
D1
S
R54
R51
● AC/DC adapter
● White goods
● Other SMPS
R52
C53
C52 R53
8
7
6
U51
5
D2
D/ST D/ST D/ST
NC D/ST
C4
R2
U1
R56
GND
STR3A400
C2
D
S/OCP VCC GND FB/OLP
1
2
ROCP
3
4
C3
PC1
CY
TC_STR3A400_1_R2
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
1
STR3A400 Series
CONTENTS
Description ------------------------------------------------------------------------------------------------------ 1
CONTENTS ---------------------------------------------------------------------------------------------------- 2
1. Absolute Maximum Ratings ----------------------------------------------------------------------------- 3
2. Electrical Characteristics -------------------------------------------------------------------------------- 4
3. Performance Curves -------------------------------------------------------------------------------------- 5
3.1 Derating Curves ------------------------------------------------------------------------------------- 5
3.2 MOSFET Safe Operating Area Curves --------------------------------------------------------- 6
3.3 Ambient Temperature versus Power Dissipation Curves ----------------------------------- 7
3.4 Transient Thermal Resistance Curves ---------------------------------------------------------- 8
4. Block Diagram --------------------------------------------------------------------------------------------- 9
5. Pin Configuration Definitions --------------------------------------------------------------------------- 9
6. Typical Application ------------------------------------------------------------------------------------- 10
7. External Dimensions ------------------------------------------------------------------------------------ 11
8. Marking Diagram --------------------------------------------------------------------------------------- 11
9. Operational Description ------------------------------------------------------------------------------- 12
9.1 Startup Operation --------------------------------------------------------------------------------- 12
9.2 Undervoltage Lockout (UVLO) ---------------------------------------------------------------- 12
9.3 Bias Assist Function------------------------------------------------------------------------------- 12
9.4 Soft Start Function -------------------------------------------------------------------------------- 13
9.5 Constant Output Voltage Control-------------------------------------------------------------- 13
9.6 Leading Edge Blanking Function -------------------------------------------------------------- 14
9.7 Random Switching Function -------------------------------------------------------------------- 14
9.8 Automatic Standby Function ------------------------------------------------------------------- 14
9.9 Step Drive Control -------------------------------------------------------------------------------- 15
9.10 Overcurrent Protection (OCP) ----------------------------------------------------------------- 16
9.10.1 OCP Operation ------------------------------------------------------------------------------ 16
9.10.2 OCP Input Compensation Function ----------------------------------------------------- 16
9.11 Overload Protection (OLP) ---------------------------------------------------------------------- 17
9.12 Overvoltage Protection (OVP) ------------------------------------------------------------------ 17
9.13 Thermal Shutdown (TSD) ----------------------------------------------------------------------- 18
10. Design Notes ---------------------------------------------------------------------------------------------- 18
10.1 External Components ---------------------------------------------------------------------------- 18
10.1.1 Input and Output Electrolytic Capacitor ----------------------------------------------- 18
10.1.2 S/OCP Pin Peripheral Circuit ------------------------------------------------------------ 19
10.1.3 VCC Pin Peripheral Circuit --------------------------------------------------------------- 19
10.1.4 FB/OLP Pin Peripheral Circuit ---------------------------------------------------------- 19
10.1.5 Snubber Circuit ------------------------------------------------------------------------------ 19
10.1.6 Peripheral Circuit of Secondary-side Shunt Regulator ------------------------------ 19
10.1.7 Transformer ---------------------------------------------------------------------------------- 19
10.2 PCB Trace Layout and Component Placement --------------------------------------------- 20
11. Pattern Layout Example ------------------------------------------------------------------------------- 22
12. Reference Design of Power Supply ------------------------------------------------------------------ 23
OPERATING PRECAUTIONS -------------------------------------------------------------------------- 25
IMPORTANT NOTES ------------------------------------------------------------------------------------- 26
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
2
STR3A400 Series
1.
Absolute Maximum Ratings
● The polarity value for current specifies a sink as "+," and a source as "−," referencing the IC.
● Unless otherwise specified TA = 25 °C, 5 pin = 6 pin = 7 pin = 8 pin
Parameter
Symbol
Conditions
Pins
Rating
Units
3.6
Drain Peak Current(1)
IDPEAK
Single pulse
8–1
5.2
ILPEAK = 2.13 A
Avalanche Energy(2)(3)
EAS
ILPEAK = 2.46 A
8–1
3A451 / 51D
A
3A455 / 55D
53
3A451 / 51D
mJ
110
1–3
−2~6
V
VCC Pin Voltage
VCC
2–3
32
V
FB/OLP Pin Voltage
VFB
4–3
− 0.3 ~ 14
V
FB/OLP Pin Sink Current
IFB
4–3
1.0
mA
VD/ST
8−3
−1 ~ VDSS
V
D/ST Pin Voltage
1.68
MOSFET Power
Dissipation(4)
PD1
(5)
8–1
1.76
3A453 / 53D
3A455 / 55D
VS/OCP
S/OCP Pin Voltage
3A453 / 53D
7.2
72
ILPEAK = 3.05 A
Notes
3A451 / 51D
W
1.81
3A453 / 53D
3A455 / 55D
Control Part Power
Dissipation
Operating Ambient
Temperature
Storage Temperature
PD2
2–3
1.3
W
TOP
−
− 40 ~ 125
°C
Tstg
−
− 40 ~ 125
°C
Channel Temperature(6)
Tch
−
150
°C
VCC × ICC
(1)
Refer to 3.2 MOSFET Safe Operating Area Curves
Refer to Figure 3-2 Avalanche Energy Derating Coefficient Curve
(3)
Single pulse, VDD = 99 V, L = 20 mH
(4)
Refer to Section 3.3 Ta-PD1 Curve
(5)
When embedding this hybrid IC onto the printed circuit board (cupper area in a 15 mm × 15 mm)
(6)
Recommended frame temperature in operation, TF, is 115 °C (max.)
(2)
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
3
STR3A400 Series
2.
Electrical Characteristics
● The polarity value for current specifies a sink as "+," and a source as "−," referencing the IC.
● Unless otherwise specified TA = 25 °C, VCC = 18 V, 5 pin = 6 pin = 7 pin = 8 pin
Parameter
Symbol
Conditions
Pins
Min.
Typ.
Max.
Units
Notes
VCC(ON)
2−3
13.8
15.0
16.2
V
VCC(OFF)
2−3
7.6
8.5
9.2
V
2−3
−
1.7
3.0
mA
VST(ON)
8−3
40
47
55
V
ICC(ST)
VCC = 13.5 V 2 − 3
− 4.5
− 2.5
− 1.2
mA
2−3
8.0
9.6
10.5
V
fOSC(AVG)
8−3
58
65
72
kHz
Δf
8−3
−
5.4
−
kHz
4−3
− 110
− 72
− 40
µA
IFB(MIN)
4−3
− 21
− 13
−5
µA
VFB(FDS)
1−8
2.64
3.30
3.96
2.40
3.00
3.60
3A455 / 55D
2.40
3.00
3.60
3A451 / 51D
3A453 / 53D
2.10
2.62
3.14
23
30
37
1.40
1.53
1.66
1.25
1.37
1.49
Power Supply Startup Operation
Operation Start Voltage
Operation Stop Voltage
(1)
Circuit Current in Operation
Startup Circuit Operation
Voltage
Startup Current
Startup Current Biasing
Threshold Voltage
Normal Operation
Average Switching Frequency
Switching Frequency
Modulation Deviation
Maximum Feedback Current
Minimum Feedback Current
ICC(ON)
VCC(BIAS)
IFB(MAX)
VCC = 12 V
ICC=−500µA
VCC = 12 V
Light Load Operation
FB/OLP Pin Starting Voltage
of Frequency Decreasing
FB/OLP Pin Ending Voltage
of Frequency Decreasing
Minimum Switching
Frequency
Standby Operation
Oscillation Stop FB Voltage
1−8
VFB(FDE)
fOSC(MIN)
5−8
VFB(OFF)
4−3
V
V
3A451 / 51D
3A453 / 53D
3A455 / 55D
kHz
V
3A451 / 51D
3A453 / 53D
3A455 / 55D
Protection
Maximum ON Duty
Leading Edge Blanking Time
OCP Compensation
Coefficient
OCP Compensation ON Duty
OCP Threshold Voltage at
Zero ON Duty
OCP Threshold Voltage at
36% ON Duty
OCP Threshold Voltage
During LEB (tBW)
OLP Threshold Voltage
OLP Operation Current
(1)
DMAX
8−3
70
75
80
%
tBW
−
−
330
−
ns
DPC
−
−
17.3
−
mV/μs
DDPC
−
−
36
−
%
VOCP(L)
1−3
0.735
0.795
0.855
V
VOCP(H)
1−3
0.843
0.888
0.933
V
VOCP(LEB)
1−3
−
1.69
−
V
VFB(OLP)
VCC = 32 V
4−3
6.8
7.3
7.8
V
ICC(OLP)
VCC = 12 V
2−3
−
260
−
µA
VCC(BIAS) > VCC(OFF) always.
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
4
STR3A400 Series
Parameter
Symbol
Pins
Min.
Typ.
Max.
Units
tOLP
−
55
75
90
ms
VFB(CLAMP)
4−3
10.5
11.8
13.5
V
VCC(OVP)
2−3
27.0
29.1
31.2
V
Tj(TSD)
−
127
145
−
°C
Tj(TSD)HYS
−
−
80
−
°C
OLP Delay Time
FB/OLP Pin Clamp Voltage
OVP Threshold Voltage
Thermal Shutdown Operating
Temperature
Thermal Shutdown Hysteresis
Temperature
MOSFET
Drain-to-Source Breakdown
Voltage
Drain Leakage Current
On Resistance
Notes
3A4××D
VDSS
IDS = 300 µA
8–1
650
−
−
V
IDSS
VDS = VDSS
8–1
−
−
300
μA
−
−
4.0
−
−
1.9
−
−
1.1
−
−
250
ns
−
−
18
°C/W
3A451 / 51D
3A453 / 53D
−
−
17
°C/W
3A455 / 55D
RDS(ON)
Switching Time
Conditions
IDS = 0.4 A
8–1
tf
8–1
θch-C
−
3A451 / 51D
Ω
3A453 / 53D
3A455 / 55D
Thermal Resistance
Channel to Case Thermal
Resistance(2)
(2)
θch-C is thermal resistance between channel and case. Case temperature (TC) is measured at the center of the case top
surface.
3.
3.1
Performance Curves
Derating Curves
EAS Temperature Derating Coefficient (%)
Safe Operating Area
Temperature Derating Coefficient (%)
100
80
60
40
20
0
0
25
50
75
100
125
150
100
80
60
40
20
0
25
75
100
125
150
Channel Temperature, Tch (°C)
Channel Temperature, Tch (°C)
Figure 3-1 SOA Temperature Derating Coefficient Curve
50
Figure 3-2 Avalanche Energy Derating Coefficient Curve
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
5
STR3A400 Series
3.2
MOSFET Safe Operating Area Curves
When the IC is used, the safe operating area curve should be multiplied by the temperature derating coefficient
derived from Figure 3-1. The broken line in the safe operating area curve is the drain current curve limited by
on-resistance.
Unless otherwise specified, TA = 25 °C, Single pulse.
● STR3A451 / 51D
● STR3A453 / 53D
1ms
0.1
1
S_STR3A453x_R1
1
0.1ms
Drain Current, ID (A)
Drain Current, ID (A)
0.1ms
S_STR3A451x_R1
10
10
1ms
0.1
0.01
0.01
1
10
100
1000
1
10
100
1000
Drain-to-Source Voltage (V)
Drain-to-Source Voltage (V)
10
Drain Current, ID (A)
0.1ms
1
S_STR3A455x_R1
● STR3A455 / 55D
1ms
0.1
0.01
1
10
100
1000
Drain-to-Source Voltage (V)
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
6
STR3A400 Series
Ambient Temperature versus Power Dissipation Curves
PD1 = 1.68 W
0
25
50
75
100
125
150
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
PD1_STR3A453x_R2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
● STR3A453 / 53D
PD1_STR3A451x_R2
Power Dissipation, PD1 (W)
● STR3A451 / 51D
Power Dissipation, PD1 (W)
3.3
PD1 = 1.76 W
0
25
50
75
100
125
150
Ambient Temperature, TA (°C )
Ambient Temperature, TA (°C )
● STR3A455 / 55D
PD1 = 1.81 W
1.8
Power Dissipation, PD1 (W)
PD1_STR3A455x_R2
2.0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
25
50
75
100
125
150
Ambient Temperature, TA (°C )
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
7
STR3A400 Series
3.4
Transient Thermal Resistance Curves
● STR3A451 /51D
TR_STR3A451x_R1
Transient Thermal Resistance
θch-c (°C/W)
10
1
0.1
0.01
1µ
10µ
100µ
1m
10m
100m
1m
10m
100m
1m
10m
100m
Time (s)
● STR3A453 / 53D
TR_STR3A453x_R1
Transient Thermal Resistance
θch-c (°C/W)
10
1
0.1
0.01
1µ
10µ
100µ
Time (s)
TR_STR3A455x_R1
● STR3A455 / 55D
Transient Thermal Resistance
θch-c (°C/W)
10
1
0.1
0.01
1µ
10µ
100µ
Time (s)
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
8
STR3A400 Series
4.
Block Diagram
VCC
D/ST
2
STARTUP
UVLO
REG
PWM OSC
S Q
VREG
OVP
5~8
TSD
DRV
R
OCP
VCC
OLP
Feedback
Control
FB/OLP
Drain Peak Current
Compensation
S/OCP
LEB
4
1
GND
Slope
Compensation
3
BD_STR3A400_R1
5.
Pin Configuration Definitions
Pin
Name
S/OCP
1
8
D/ST
1
S/OCP
VCC
2
7
D/ST
2
VCC
GND
3
6
D/ST
3
GND
FB/OLP
4
5
D/ST
4
FB/OLP
Descriptions
MOSFET source and input of Overcurrent
Protection (OCP) signal
Power supply voltage input for control part and
input of Overvoltage Protection (OVP) signal
Ground
Input of constant voltage control signal and input
of Overload Protection (OLP) signal
5
6
7
D/ST
MOSFET drain and input of startup current
8
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
9
STR3A400 Series
6.
Typical Application
The PCB traces D/ST pins should be as wide as possible, in order to enhance thermal dissipation.
In applications having a power supply specified such that V DS has large transient surge voltages, a clamp snubber
circuit of a capacitor-resistor-diode (CRD) combination should be added on the primary winding P, or a damper
snubber circuit of a capacitor (C) or a resistor-capacitor (RC) combination should be added between the D/ST pin and
the S/OCP pin.
CRD clamp snubber
L51
BR1
D51
T1
VAC
VOUT
R1
C5
PC1
C1
P
R55
C51
D1
S
R54
R51
R52
C53
C52 R53
8
7
6
U51
5
D2
D/ST D/ST D/ST
NC D/ST
C4
U1
R56
GND
STR3A400
C（RC）
dumper snubber
R2
C2
D
S/OCP VCC GND FB/OLP
1
2
ROCP
3
4
C3
PC1
CY
TC_STR3A400_2_R2
Figure 6-1 Typical application
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
10
STR3A400 Series
7.
External Dimensions
● DIP8
NOTES:
1) Dimension is in millimeters
2) Pb-free. Device composition compliant with the RoHS directive
8.
Marking Diagram
8
Part Number (3A4×× / 3A4××D)
YMD
1
Lot Number
Y = Last Digit of Year (0-9)
M = Month (1-9,O,N or D)
D =Period of days (1 to 3)
1 : 1st to 10th
2 : 11th to 20th
3 : 21st to 31st
Sanken Control Number
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
11
STR3A400 Series
9.
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).
9.1
Startup Operation
VAC
C1
(2)
I CC(ST )
: Startup time of the IC (s)
: Initial voltage on the VCC pin (V)
Undervoltage Lockout (UVLO)
P
Circuit current, ICC
5-8
D/ST
2
D2
C2
GND
VCC ( ON )－VCC( INT )
Figure 9-2 shows the relationship of VCC pin voltage
and circuit current ICC. When the VCC pin voltage
decreases to VCC(OFF) = 8.5 V, the control circuit stops
operation by UVLO (Undervoltage Lockout) circuit, and
reverts to the state before startup.
T1
BR1
VCC
where,
tSTART
VCC(INT)
9.2
Figure 9-1 shows the circuit around the VCC pin.
U1
t START  C2 ×
R2
VD
Stop
D
Start
3
VCC（OFF）
Figure 9-1 VCC pin peripheral circuit
The IC incorporates the startup circuit. The circuit is
connected to the D/ST pin. When D/ST pin voltage
reaches to Startup Circuit Operation Voltage
VST(ON) = 47 V, the startup circuit starts operation.
During the startup process, the constant current,
ICC(ST) = − 2.5 mA, charges C2 at the VCC pin. When
VCC pin voltage increases to VCC(ON) = 15.0 V, the
control circuit starts switching operation. During the IC
operation, the voltage rectified the auxiliary winding
voltage, VD, of Figure 9-1 becomes a power source to
the VCC pin.
After switching operation begins, the startup circuit
turns off automatically so that its current consumption
becomes zero. The approximate value of auxiliary
winding voltage is about 18V, taking account of the
winding turns of D winding so that the VCC pin voltage
becomes Equation (1) within the specification of input
and output voltage variation of power supply.
VCC( BIAS) (max .)  VCC  VCC(OVP ) (min .)
⇒10.5 (V) < VCC < 27.0 (V)
(1)
The startup time of the IC is determined by C2
capacitor value. The approximate startup time t START is
calculated as follows:
VCC（ON） VCC pin
voltage
Figure 9-2 Relationship between
VCC pin voltage and ICC
9.3
Bias Assist Function
By the Bias Assist Function, the startup failure is
prevented and the latched state is kept.
The Bias Assist Function is activated in the following
condition. Where, VFB(OFF) is the FB/OLP Pin Oscillation
Stop Threshold Voltage, VCC(BIAS) is the Startup Current
Biasing Threshold Voltage.
● Auto-restart type (STR3A4××D)
When FB pin voltage is VFB(OFF) or less and VCC pin
voltage decreases to VCC(BIAS) = 9.6 V, the Bias Assist
Function is activated.
● Latched shutdown type (STR3A4××)
When VCC pin voltage decreases to VCC(BIAS) = 9.6 V
in the following condition, the Bias Assist Function is
activated.
FB pin voltage is VFB(OFF) or less
or the IC is in the latched state due to activating the
protection function.
When the Bias Assist Function is activated, the VCC
pin voltage is kept almost constant voltage, VCC(BIAS) by
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
12
STR3A400 Series
providing the startup current, ICC(ST), from the startup
circuit. Thus, the VCC pin voltage is kept more than
VCC(OFF).
Since the startup failure is prevented by the Bias
Assist Function, the value of C2 connected to the VCC
pin can be small. Thus, the startup time and the response
time of the Overvoltage Protection (OVP) become
shorter.
The operation of the Bias Assist Function in startup is
as follows. It is necessary to check and adjust the startup
process based on actual operation in the application, so
that poor starting conditions may be avoided.
Figure 9-3 shows the VCC pin voltage behavior
during the startup period. After the VCC pin voltage
increases to VCC(ON) = 15.0 V at startup, the IC starts the
operation. Then circuit current increases and the VCC
pin voltage decreases. At the same time, the auxiliary
winding voltage, VD, increases in proportion to output
voltage. These are all balanced to produce the VCC pin
voltage.
When the VCC pin voltage is decrease to
VCC(OFF) = 8.5 V in startup operation, the IC stops
switching operation and a startup failure occurs. When
the output load is light at startup, the output voltage may
become more than the target voltage due to the delay of
feedback circuit. In this case, the FB pin voltage is
decreased by the feedback control. When the FB pin
voltage decreases to VFB(OFF) or less, the IC stops
switching operation and the VCC pin voltage decreases.
When the VCC pin voltage decreases to VCC(BIAS), the
Bias Assist Function is activated and the startup failure
is prevented.
VCC pin
voltage
Target operating
voltage
Increase with rising of
output voltage
Bias assist period
Startup failure
Time
Figure 9-3 VCC pin voltage during startup period
9.4
VCC pin
voltage
Startup of IC Startup of SMPS
Normal opertion
tSTART
VCC(ON)
VCC(OFF)
Time
D/ST pin
current, ID
Soft start period
approximately 8.75 ms (fixed)
Limited by OCP operation
tLIM < tOLP (min.)
Time
Figure 9-4 VCC and ID behavior during startup
Startup success
IC starts operation
VCC(ON)
VCC(BIAS)
VCC(OFF)
Section 9.6) is deactivated during the soft start period,
there is the case that ON time is less than the leading
edge blanking time, tBW = 330 ns.
After the soft start period, D/ST pin current, ID, is
limited by the Overcurrent Protection (OCP), until the
output voltage increases to the target operating voltage.
This period is given as tLIM.
In case tLIM is longer than the OLP Delay Time, tOLP,
the output power is limited by the Overload Protection
(OLP) operation.
Thus, it is necessary to adjust the value of output
capacitor and the turn ratio of auxiliary winding D so
that the tLIM is less than tOLP = 55 ms (min.).
Soft Start Function
Figure 9-4 shows the behavior of VCC pin voltage
and drain current during the startup period.
The IC activates the soft start circuitry during the
startup period. Soft start time is fixed to around 8.75 ms.
during the soft start period, overcurrent threshold is
increased step-wisely (7 steps). This function reduces
the voltage and the current stress of a power MOSFET
and the secondary side rectifier diode.
Since the Leading Edge Blanking Function (refer to
9.5
Constant Output Voltage Control
The IC achieves the constant voltage control of the
power supply output by using the current-mode control
method, which enhances the response speed and
provides the stable operation. The FB/OLP pin voltage
is internally added the slope compensation at the
feedback control (refer to Section 4. Block Diagram),
and the target voltage, VSC, is generated. The IC
compares the voltage, VROCP, of a current detection
resistor with the target voltage, VSC, by the internal FB
comparator, and controls the peak value of VROCP so that
it gets close to VSC, as shown in Figure 9-5 and Figure
9-6.
● Light load conditions
When load conditions become lighter, the output
voltage, VOUT, increases. Thus, the feedback current
from the error amplifier on the secondary-side also
increases. The feedback current is sunk at the FB/OLP
pin, transferred through a photo-coupler, PC1, and the
FB/OLP pin voltage decreases. Thus, VSC decreases,
and the peak value of VROCP is controlled to be low,
and the peak drain current of I D decreases.
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
13
STR3A400 Series
This control prevents the output voltage from
increasing.
Target voltage
without slope compensation
● Heavy load conditions
When load conditions become greater, the IC
performs the inverse operation to that described above.
Thus, VSC increases and the peak drain current of ID
increases.
This control prevents the output voltage from
decreasing.
In the current mode control method, when the drain
current waveform becomes trapezoidal in continuous
operating mode, even if the peak current level set by the
target voltage is constant, the on-time fluctuates based
on the initial value of the drain current.
This results in the on-time fluctuating in multiples of
the fundamental operating frequency as shown in Figure
9-7. This is called the subharmonics phenomenon.
In order to avoid this, the IC incorporates the Slope
Compensation Function. Because the target voltage is
added a down-slope compensation signal, which reduces
the peak drain current as the on-duty gets wider relative
to the FB/OLP pin signal to compensate V SC, the
subharmonics phenomenon is suppressed.
Even if subharmonic oscillations occur when the IC
has some excess supply being out of feedback control,
such as during startup and load shorted, this does not
affect performance of normal operation.
U1
S/OCP
1
T
tON2
T
T
Figure 9-7 Drain current, ID, waveform
in subharmonic oscillation
9.6
Leading Edge Blanking Function
The constant voltage control of output of the IC uses
the peak-current-mode control method.
In peak-current-mode control method, there is a case
that the power MOSFET turns off due to unexpected
response of a FB comparator or Overcurrent Protection
(OCP) circuit to the steep surge current in turning on a
power MOSFET.
In order to prevent this response to the surge voltage
in turning-on the power MOSFET, the Leading Edge
Blanking, tBW = 330 ns is built-in. During tBW, the OCP
threshold voltage becomes VOCP(LEB) = 1.69 V in order
not to respond to the turn-on drain current surge (refer to
Section 9.10).
GND FB/OLP
3
9.7
4
PC1
ROCP
VROCP
tON1
C3
IFB
Figure 9-5 FB/OLP pin peripheral circuit
Target voltage including
slope compensation
-
VSC
+
VROCP
FB comparator
Voltage on both
sides of ROCP
Drain current,
ID
Figure 9-6 Drain current, ID, and FB comparator
operation in steady operation
Random Switching Function
The IC modulates its switching frequency randomly
by superposing the modulating frequency on fOSC(AVG) in
normal operation. This function reduces the conduction
noise compared to others without this function, and
simplifies noise filtering of the input lines of power
supply.
9.8
Automatic Standby Function
The IC has Automatic Standby Function to achieve
higher efficiency at light load. In order to reduce the
switching loss, the Automatic Standby Function
automatically changes the oscillation mode to green
mode or burst oscillation mode (refer to Figure 9-8).
When the output load becomes lower, FB/OLP pin
voltage decreases. When the FB/OLP pin voltage
decreases to VFB(FDS) or less, the green mode is activated
and the oscillation frequency starts decreasing. When the
FB/OLP pin voltage becomes VFB(FDE), the oscillation
frequency stops decreasing (refer to Table 9-1). At this
point, the oscillation frequency becomes fOSC(MIN) = 30
kHz. When the FB/OLP pin voltage further decreases
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
14
STR3A400 Series
and becomes the standby operation point, the burst
oscillation mode is activated. As shown in Figure 9-9,
the burst oscillation mode consists of the switching
period and the non-switching period. The oscillation
frequency during the switching period is the Minimum
Frequency, fOSC(MIN) = 30 kHz.
Switching
frequency
fOSC
fOSC(AVG)
standby mode, the power loss increases. Therefore, the
VCC pin voltage should be more than VCC(BIAS), for
example, by adjusting the turns ratio of the auxiliary
winding and the secondary-side winding and/or reducing
the value of R2 in Figure 10-2 (refer to Section 10.1).
9.9
Normal
operation
fOSC(MIN)
Burst oscillation
Green mode
Standby power
Output power, PO
Figure 9-8 Relationship between PO and fOSC
Step Drive Control
Figure 9-10 shows a flyback control circuit. The both
end of secondary rectification diode (D51) is generated
surge voltage when a power MOSFET turns on. Thus,
VRM of D51 should be set in consideration of the surge.
The IC optimally controls the gate drive of the
internal power MOSFET (Step drive control) depending
on the load condition. The step drive control reduces the
surge voltage of D51 when the power MOSFET turns on
(See Figure 9-11). Since VRM of D51 can be set to lower
value than usual, the price reduction and the increasing
circuit efficiency are achieved by using a diode of low
VF.
Table 9-1 FB/OLP Pin Starting and Ending Voltage of
Frequency Decreasing
Products
VFB(FDS) (Typ.)
VFB(FDE) (Typ.)
STR3A451 / 51D
STR3A453 / 53D
3.30 V
3.00 V
STR3A455 / 55D
3.00 V
2.62 V
ID
VD51
BR1
VAC
T1
D51
Switching period
Non-switching period
P1
C1
S1
C51
ID
5-8
D/ST
U1
S/OCP
1
ROCP
fOSC(MIN)
Time
Figure 9-10 Flyback control circuit
Figure 9-9 Switching waveform at burst oscillation
Generally, in order to improve efficiency under light
load conditions, the frequency of the burst mode
becomes just a few kilohertz. Because the IC suppresses
the peak drain current well during burst mode, audible
noises can be reduced.
The IC has some detection delay time. The higher the
AC input voltage is, the steeper the slope of the drain
current, ID is. Thus, the peak of ID at automatic standby
mode becomes high at a high AC input voltage.
It is necessary to consider that the burst frequency
becomes low at a high AC input.
If VCC pin voltage decreases to VCC(BIAS) = 9.6 V
during the transition to the burst mode, Bias Assist
Function is activated and stabilizes the standby mode,
because the Startup Current, ICC(ST), is provided to the
VCC pin so that the VCC pin voltage does not decrease
to VCC(OFF). However, if the Bias Assist Function is
always activated during steady-state operation including
ID
Time
Time
Reducing surge voltage
VD51
Time
Without step drive
control
Time
With step drive
control
Figure 9-11 ID and VD51 waveforms
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
15
STR3A400 Series
9.10.1 OCP Operation
Overcurrent Protection (OCP) detects each drain peak
current level of a power MOSFET on pulse-by-pulse
basis, and limits the output power when the current level
reaches to OCP threshold voltage.
During Leading Edge Blanking Time, the OCP
threshold voltage becomes VOCP(LEB) = 1.69 V which is
higher than the normal OCP threshold voltage as shown
in Figure 9-12. Changing to this threshold voltage
prevents the IC from responding to the surge voltage in
turning-on the power MOSFET. This function operates
as protection at the condition such as output windings
shorted or unusual withstand voltage of secondary-side
rectifier diodes.
When the power MOSFET turns on, the surge voltage
width of the S/OCP pin should be less than tBW, as
shown in Figure 9-12. In order to prevent surge voltage,
pay extra attention to ROCP trace layout (refer to Section
10.2). In addition, if a C (RC) damper snubber of Figure
9-13 is used, reduce the capacitor value of damper
snubber.
tBW
VOCP(LEB)
VOCP’
9.10.2 OCP Input Compensation Function
ICs with PWM control usually have some propagation
delay time. The steeper the slope of the actual drain
current at a high AC input voltage is, the larger the
detection voltage of actual drain peak current is,
compared to VOCP. Thus, the peak current has some
variation depending on AC input voltage in OCP state.
In order to reduce the variation of peak current in OCP
state, the IC has Input Compensation Function.
This function corrects OCP threshold voltage
depending on the AC input voltage, as shown in Figure
9-14.
When the AC input voltage is low (ON Duty is broad),
the OCP threshold voltage is controlled to become high.
The difference of peak drain current become small
compared with the case where the AC input voltage is
high (ON Duty is narrow).
The compensation signal depends on ON Duty. The
relation between the ON Duty and the OCP threshold
voltage after compensation VOCP' is expressed as
Equation (3). When ON Duty is broader than 36 %, the
VOCP' becomes a constant value VOCP(H) = 0.888 V
1.0
OCP Threshold Voltage after
compensation, VOCP'
9.10 Overcurrent Protection (OCP)
VOCP(H)
VOCP(L)
DDPC=36%
0.5
Surge pulse voltage width at turning-on
Figure 9-12 S/OCP pin voltage
0
50
DMAX=75%
100
ON Duty (%)
Figure 9-14 Relationship between ON Duty and Drain
Current Limit after compensation
C（RC）
Damper snubber
T1
VOCP '  VOCP ( L)  DPC  ONTime
D51
C1
C51
5~8
D/ST
U1
S/OCP
1
 VOCP ( L )  DPC 
C（RC）
Damper snubber
ROCP
Figure 9-13 Damper snubber
ONDuty
f OSC ( AVG )
(3)
where,
VOCP(L): OCP Threshold Voltage at Zero ON Duty (V)
DPC: OCP Compensation Coefficient (mV/μs)
ONTime: On-time of power MOSFET (μs)
ONDuty: On duty of power MOSFET (%)
fOSC(AVG): Average PWM Switching Frequency (kHz)
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
16
STR3A400 Series
9.11 Overload Protection (OLP)
Figure 9-15 shows the FB/OLP pin peripheral circuit,
and Figure 9-16 shows each waveform for Overload
Protection (OLP) operation.
U1
GND
FB/OLP
1
8
VCC
7
PC1
C5
D2 R2
9.12 Overvoltage Protection (OVP)
When a voltage between the VCC pin and the GND
pin increases to VCC(OVP) = 29.1 V or more, Overvoltage
Protection (OVP) is activated. The IC has two operation
types of OVP. One is latched shutdown. The other is
auto-restart.
When VCC pin voltage is provided by using auxiliary
winding of transformer, the VCC pin voltage is
proportional to output voltage. Thus, the VCC pin can
detect the overvoltage conditions such as output voltage
detection circuit open. The approximate value of output
voltage VOUT(OVP) in OVP condition is calculated by
using Equation (4).
C4
D
Figure 9-15 FB/OLP pin peripheral circuit
VCC pin voltage
the circuit current increases. After that, the VCC pin
voltage decreases. When the VCC pin voltage decreases
to VCC(OFF) = 8.5 V, the control circuit stops operation.
Skipping the UVLO operation of VCC(OFF) (refer to
Section 9.2), the intermittent operation makes the
non-switching interval longer and restricts the
temperature rise of the power MOSFET.
When the abnormal condition is removed, the IC
returns to normal operation automatically.
Non-switching
interval
Non-switching
interval
VCC(ON)
VCC(OFF)SKP
VCC(OFF)
FB/OLP pin voltage
tOLP
tOLP
tOLP
VOUT(OVP) 
VFB(OLP)
Drain current,
ID
Figure 9-16 OLP operational waveforms
When the peak drain current of ID is limited by
Overcurrent Protection operation, the output voltage,
VOUT, decreases and the feedback current from the
secondary photo-coupler becomes zero. Thus, the
feedback current, IFB, charges C5 connected to the
FB/OLP pin and FB/OLP pin voltage increases. When
the FB/OLP pin voltage increases to VFB(OLP) = 7.3 V or
more for the OLP delay time, tOLP = 75 ms or more, the
OLP is activated, the IC stops switching operation.
During OLP operation, the intermittent operation by
VCC pin voltage repeats and reduces the stress of parts
such as a power MOSFET and secondary side rectifier
diodes.
When the OLP is activated, the IC stops switching
operation, and the VCC pin voltage decreases.
During OLP operation, the Bias Assist Function is
disabled. When the VCC pin voltage decreases to
VCC(OFF)SKP (about 9 V), the startup current flows, and
the VCC pin voltage increases. When the VCC pin
voltage increases to VCC(ON), the IC starts operation, and
VOUT ( NORMAL )
VCC( NORMAL )
 29.1 (V)
(4)
where,
VOUT(NORMAL): Output voltage in normal operation
VCC(NORMAL): VCC pin voltage in normal operation
● Latched Shutdown type: STR3A4××
When the OVP is activated, the IC stops switching
operation at the latched state. In order to keep the
latched state, when VCC pin voltage decreases to
VCC(BIAS), the Bias Assist Function is activated and the
VCC pin voltage is kept to over the VCC(OFF).
Releasing the latched state is done by turning off the
input voltage and by dropping the VCC pin voltage
below VCC(OFF).
● Auto-Restart Type: STR3A4××D
When the OVP is activated, the IC stops switching
operation. During OVP operation, the Bias Assist
Function is disabled, the intermittent operation by the
UVLO is repeated (refer to Section 9.11). When the
fault condition is removed, the IC returns to normal
operation automatically (refer to Figure 9-17).
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
17
STR3A400 Series
VCC pin voltage
VCC(OVP)
Junction Temperature,
Tj
VCC(ON)
Tj(TSD)−Tj(TSD)HYS
Tj(TSD)
VCC(OFF)
Bias assist
function
Drain current,
ID
ON
ON
OFF
OFF
VCC pin voltage
VCC(ON)
VCC(BIAS)
VCC(OFF)
Figure 9-17 OVP operational waveforms
Drain current
ID
9.13 Thermal Shutdown (TSD)
Figure 9-18 TSD operational waveforms
When the temperature of control circuit increases to
Tj(TSD) = 145 °C or more, Thermal Shutdown (TSD) is
activated. The IC has two operation types of TSD. One
is latched shutdown, the other is auto-restart.
● Latched Shutdown type: STR3A4××
When TSD is activated, the IC stops switching
operation at the latched state. In order to keep the
latched state, when VCC pin voltage decreases to
VCC(BIAS), the Bias Assist Function is activated and the
VCC pin voltage is kept to over VCC(OFF).
Releasing the latched state is done by turning off the
input voltage and by dropping the VCC pin voltage
below VCC(OFF).
● Auto-Restart Type: STR3A4××D
Figure 9-18 shows the TSD operational waveforms.
This type has the thermal hysteresis of TSD.
When TSD is activated, and the IC stops switching
operation. After that, VCC pin voltage decreases.
When the VCC pin voltage decreases to VCC(BIAS), the
Bias Assist Function is activated and the VCC pin
voltage is kept to over the VCC(OFF).
When the temperature reduces to less than
Tj(TSD)−Tj(TSD)HYS, the Bias Assist Function is disabled
and the VCC pin voltage decreases to VCC(OFF). At that
time, the IC stops operation and reverts to the state
before startup. After that, the startup circuit is
activated, the VCC pin voltage increases to VCC(ON),
and the IC starts switching operation again.
In this way, the intermittent operation by the TSD and
the UVLO is repeated while there is an excess thermal
condition.
When the fault condition is removed, the IC returns to
normal operation automatically.
10. Design Notes
10.1 External Components
Take care to use properly rated, including derating as
necessary and proper type of components.
CRD clamp snubber
BR1
T1
VAC
C5
C1
R1
P
D1
8
C4
7
6
D2
5
R2
D/ST D/ST D/ST
NC D/ST
U1
C2
STR3A400
C（RC）
Damper snubber
D
S/OCP VCC GND FB/OLP
1
2
ROCP
3
4
C3
PC1
Figure 10-1 The IC peripheral circuit
10.1.1 Input and Output Electrolytic
Capacitor
Apply proper derating to ripple current, voltage, and
temperature rise. Use of high ripple current and low
impedance types, designed for switch mode power
supplies, is recommended.
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
18
STR3A400 Series
10.1.2 S/OCP Pin Peripheral Circuit
In Figure 10-1, ROCP is the resistor for the current
detection. Since high frequency switching current flows
to ROCP, choose the resistor of low inductance and high
power dissipation capability.
10.1.3 VCC Pin Peripheral Circuit
The value of C2 in Figure 10-1 is generally
recommended to be 10 µF to 47 μF (refer to Section 9.1
Startup Operation, because the startup time is
determined by the value of C2)
In actual power supply circuits, there are cases in
which the VCC pin voltage fluctuates in proportion to
the output current, IOUT (see Figure 10-2), and the
Overvoltage Protection (OVP) on the VCC pin may be
activated. This happens because C2 is charged to a peak
voltage on the auxiliary winding D, which is caused by
the transient surge voltage coupled from the primary
winding when the power MOSFET turns off. For
alleviating C2 peak charging, it is effective to add some
value R2, of several tenths of ohms to several ohms, in
series with D2 (see Figure 10-1). The optimal value of
R2 should be determined using a transformer matching
what will be used in the actual application, because the
variation of the auxiliary winding voltage is affected by
the transformer structural design.
● A clamp snubber circuit of a capacitor-resistor- diode
(CRD) combination should be added on the primary
winding P.
● A damper snubber circuit of a capacitor (C) or a
resistor-capacitor (RC) combination should be added
between the D/ST pin and the S/OCP pin.
In case the damper snubber circuit is added, this
components should be connected near D/ST pin and
S/OCP pin.
10.1.6
Peripheral Circuit of
Secondary-side Shunt Regulator
Figure 10-3 shows the secondary-side detection
circuit with the standard shunt regulator IC (U51).
C52 and R53 are for phase compensation. The value
of C52 and R53 are recommended to be around 0.047 μF
to 0.47 μF and 4.7 kΩ to 470 kΩ, respectively. They
should be selected based on actual operation in the
application.
L51
T1
VOUT
(+)
D51
PC1
R55
C51
VCC pin voltage
Without R2
S
R54
R51
R52
C53
C52 R53
U51
R56
(-)
With R2
Output current, IOUT
Figure 10-3 Peripheral circuit of secondary-side shunt
regulator (U51)
Figure 10-2 Variation of VCC pin voltage and power
10.1.7 Transformer
10.1.4 FB/OLP Pin Peripheral Circuit
C3 (see Figure 10-1) is for high frequency noise
rejection and phase compensation, and should be
connected close to the FB/OLP pin and the GND pin.
The value of C3 is recommended to be about 2200 pF to
0.01 µF, and should be selected based on actual
operation in the application.
10.1.5 Snubber Circuit
In case the serge voltage of VDS is large, the circuit
should be added as follows (see Figure 10-1);
Apply proper design margin to core temperature rise
by core loss and copper loss.
Because the switching currents contain high frequency
currents, the skin effect may become a consideration.
Choose a suitable wire gauge in consideration of the
RMS current and a current density of 4 to 6 A/mm2.
If measures to further reduce temperature are still
necessary, the following should be considered to
increase the total surface area of the wiring:
● Increase the number of wires in parallel.
● Use litz wires.
● Thicken the wire gauge.
In the following cases, the surge of VCC pin voltage
becomes high.
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
19
STR3A400 Series
● The surge voltage of primary main winding, P, is high
(low output voltage and high output current power
supply designs)
● The winding structure of auxiliary winding, D, is
susceptible to the noise of winding P.
When the surge voltage of winding D is high, the
VCC pin voltage increases and the Overvoltage
Protection (OVP) may be activated. In transformer
design, the following should be considered;
● The coupling of the winding P and the secondary
output winding S should be maximized to reduce the
leakage inductance.
● The coupling of the winding D and the winding S
should be maximized.
● The coupling of the winding D and the winding P
should be minimized.
In the case of multi-output power supply, the coupling
of the secondary-side stabilized output winding, S1, and
the others (S2, S3…) should be maximized to improve
the line-regulation of those outputs
Figure 10-4 shows the winding structural examples of
two outputs.
● Winding structural example (a):
S1 is sandwiched between P1 and P2 to maximize the
coupling of them for surge reduction of P1 and P2. D
is placed far from P1 and P2 to minimize the coupling
to the primary for the surge reduction of D.
● Winding structural example (b)
P1 and P2 are placed close to S1 to maximize the
coupling of S1 for surge reduction of P1 and P2.。
D and S2 are sandwiched by S1 to maximize the
coupling of D and S1, and that of S1 and S2. This
structure reduces the surge of D, and improves the
line-regulation of outputs.
Bobbin
Margin tape
P1 S1 P2 S2 D
Margin tape
Winding structural example (a)
Bobbin
Margin tape
P1 S1 D S2 S1 P2
Margin tape
Winding structural example (b)
Figure 10-4 Winding structural examples
10.2 PCB Trace Layout and Component
Placement
Since the PCB circuit trace design and the component
layout significantly affects operation, EMI noise, and
power dissipation, the high frequency PCB trace should
be low impedance with small loop and wide trace. In
addition, the ground traces affect radiated EMI noise,
and wide, short traces should be taken into account.
Figure 10-5 shows the circuit design example.
(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.
If C1 and the IC are distant from each other, placing
a capacitor such as film capacitor (about 0.1 μF and
with proper voltage rating) close to the transformer
or the IC is recommended to reduce impedance of
the high frequency current loop.
(2) Control Ground Trace Layout
Since the operation of the IC may be affected from
the large current of the main trace that flows in
control ground trace, the control ground trace should
be separated from main trace and connected at a
single point grounding of point A in Figure 10-5 as
close to the ROCP pin 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 C2 and
the IC are distant from each other, placing a
capacitor such as film capacitor Cf (about 0.1 μF to
1.0 μF) close to the VCC pin and the GND pin is
recommended.
(4) ROCP Trace Layout
ROCP should be placed as close as possible to the
S/OCP pin. The connection between the power
ground of the main trace and the IC ground should
be at a single point ground (point A in Figure 10-5)
which is close to the base of ROCP.
(5) FB/OLP Trace Layout
The components connected to FB/OLP pin should be
as close to FB/OLP pin as possible. The trace
between the components and FB/OLP pin should be
as short as possible.
(6) Secondary 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. If this trace
is thin and long, inductance resulting from the loop
may increase surge voltage at turning off the power
MOSFET. Proper rectifier smoothing trace layout
helps to increase margin against the power MOSFET
breakdown voltage, and reduces stress on the clamp
snubber circuit and losses in it.
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
20
STR3A400 Series
(7) Thermal Considerations
Because the power MOSFET has a positive thermal
coefficient of RDS(ON), consider it in thermal design.
Since the copper area under the IC and the D/ST pin
trace act as a heatsink, its traces should be as wide as
possible.
(1) Main trace should be wide
trace and small loop
(6) Main trace of secondary side should
be wide trace and small loop
D51
T1
R1
C5
C1
P
(7)Trace of D/ST pin should beDST
wide for heat release
8
7
D/ST D/ST
C4
6
C51
D1
S
5
D2
NC
D/ST
D/ST
R2
U1
STR3A400
C2
D
S/OCP VCC GND FB/OLP
1
2
3
4
(3) Loop of the power
supply should be small
ROCP
PC1
C3
(5)The components connected to
FB/OLP pin should be as close
to FB/OLP pin as possible
A
(4)ROCP Should be as close to S/OCP pin as
possible.
CY
(2) Control GND trace should be connected at a
single point as close to the ROCP as possible
Figure 10-5 Peripheral circuit example around the IC
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
21
STR3A400 Series
11. Pattern Layout Example
The following show the two outputs PCB pattern layout example and the schematic of circuit using STR3A400 series.
The PCB pattern layout example is made usable to other ICs in common. The parts in Figure 11-2 are only used.
Figure 11-1 PCB circuit trace layout example
1
F1
L1
C10
C2
C1
D1
D2 TH1
D4
D3
L51
T1
CN51
D51
VOUT1
R5
C11
C4
3
R1
R54
R51
C56 R62
C3
J1
P1
R4
PC1
C51
R52
R53
U51
8
7
6
D/ST
D/ST
D/ST
NC
JW52
GND
D/ST
JW51
D6
S/OCP VCC
2
R60
JW53
STR3A400
1
C52
R56
5
U1
C8
C53
R57
S1
D5
R55
D52
R2
R58
R59
L52
GND FB/OLP
3
OUT2
4
C5
D
C57 R63
C54
C55
R61
C7
R3
GND
C6
PC1
C9
CN52
Figure 11-2 Circuit schematic for PCB circuit trace layout
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
22
STR3A400 Series
12. Reference Design of Power Supply
As an example, the following show the power supply specification, the circuit schematic, the bill of materials, and the
transformer specification.
● Power supply specification
IC
Input voltage
Maximum output power
Output 1
Output 2
STR3A453D
85VAC to 265VAC
34.8 W (40.4 W peak)
8 V / 0.5 A
14 V / 2.2 A (2.6 A peak)
● Circuit schematic
Refer to Figure 11-2
● Bill of materials
Symbol
F1
L1
TH1
D1
D2
D3
D4
D5
D6
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
R1
R2
R3
R4
R5
PC1
U1
T1
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(3)
(2)
(2)
(2)
(3)
Part type
Ratings(1)
Fuse
CM inductor
NTC thermistor
General
General
General
General
General
Fast recovery
Film, X2
Electrolytic
Electrolytic
Ceramic
Electrolytic
Ceramic
Ceramic
Ceramic
Ceramic, Y1
Ceramic
Ceramic
Metal oxide
General
General
General
Metal oxide
Photo-coupler
IC
250 VAC , 3 A
3.3 mH
Short
600 V, 1 A
600 V, 1 A
600 V, 1 A
600 V, 1 A
800 V, 1.2 A
200 V, 1 A
0.1 μF, 275 V
Open
150 μF, 400 V
1000 pF, 2 kV
22 μF, 50 V
0.01 μF
Open
15 pF, 2 kV
2200 pF, 250 V
Open
Open
330 kΩ, 1 W
10 Ω
0.47 Ω, 1/2 W
47 Ω, 1 W
Open
PC123 or equiv
－
Transformer
See
the specification
Recommended
Sanken Parts
EM01A
EM01A
EM01A
EM01A
SARS01
AL01Z
STR3A453D
Symbol
L51
L52
D51
D52
C51
C52
C53
C54
C55
C56
C57
R51
R52
R53
R54
R55
R56
R57
R58
R59
R60
R61
R62
R63
JW51
JW52
JW53
U51
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(2)
Part type
Inductor
Inductor
Schottky
Schottky
Electrolytic
Ceramic
Electrolytic
Electrolytic
Electrolytic
Ceramic
Ceramic
General
General
General
General, 1%
General, 1%
General, 1%
General
General
General
General, 1%
General
General
General
Shunt regulator
Ratings(1)
Short
Short
60 V, 1.5 A
100V, 10A
680 μF, 25 V
0.1 μF, 50 V
680 μF, 25 V
470 μF, 16 V
Open
Open
Open
Open
1.5 kΩ
100 kΩ
Open
Open
10 kΩ
Open
1 kΩ
6.8 kΩ
39 kΩ
Open
Open
Open
Short
Short
Short
VREF = 2.5 V
TL431 or equiv
Recommended
Sanken Parts
EK16
FMEN-210A
TL431or
equiv
(1)
Unless otherwise specified, the voltage rating of capacitor is 50 V or less and the power rating of resistor is 1/8 W or less.
It is necessary to be adjusted based on actual operation in the application.
(3)
Resistors applied high DC voltage and of high resistance are recommended to select resistors designed against electromigration or
use combinations of resistors in series to reduce applied voltage to each of them, according to the requirement of the application.
(2)
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
23
STR3A400 Series
● Transformer specification
Primary inductance, LP: 518 μH
Core size: EER-28
Al-value: 245 nH/N2 (Center gap of about 0.56 mm)
Winding specification
Symbol
Number of
turns (T)
Wire diameter
(mm)
Primary winding
P1
18
φ 0.23 × 2
Primary winding
P2
28
φ 0.30
D
S1-1
S1-2
S2-1
S2-2
12
6
6
4
4
φ 0.30 × 2
φ 0.4 × 2
φ 0.4 × 2
φ 0.4 × 2
φ 0.4 × 2
Winding
Auxiliary winding
Output 1 winding
Output 1 winding
Output 2 winding
Output 2 winding
Construction
Single-layer, solenoid
winding
Single-layer, solenoid
winding
Solenoid winding
Solenoid winding
Solenoid winding
Solenoid winding
Solenoid winding
4mm
2mm
VDC
P2
8V
D
S2-1 S1-1
P2
P1
Pin side
S2-2 S1-2
Margin tape
Margin tape
P1
S1-2
Drain
14V
VCC
D
Bobbin
Core
S1-1
S2-1
S2-2
GND
GND
Cross-section view
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
●: Start at this pin
24
STR3A400 Series
OPERATING PRECAUTIONS
In the case that you use Sanken products or design your products by using Sanken products, the reliability largely
depends on the degree of derating to be made to the rated values. Derating may be interpreted as a case that an operation
range is set by derating the load from each rated value or surge voltage or noise is considered for derating in order to
assure or improve the reliability. In general, derating factors include electric stresses such as electric voltage, electric
current, electric power etc., environmental stresses such as ambient temperature, humidity etc. and thermal stress caused
due to self-heating of semiconductor products. For these stresses, instantaneous values, maximum values and minimum
values must be taken into consideration. In addition, it should be noted that since power devices or IC’s including power
devices have large self-heating value, the degree of derating of junction temperature affects the reliability significantly.
Because reliability can be affected adversely by improper storage environments and handling methods, please
observe the following cautions.
Cautions for Storage
● Ensure that storage conditions comply with the standard temperature (5 to 35°C) and the standard relative humidity
(around 40 to 75%); avoid storage locations that experience extreme changes in temperature or humidity.
● Avoid locations where dust or harmful gases are present and avoid direct sunlight.
● Reinspect for rust on leads and solderability of the products that have been stored for a long time.
Cautions for Testing and Handling
When tests are carried out during inspection testing and other standard test periods, protect the products from power
surges from the testing device, shorts between the product pins, and wrong connections. Ensure all test parameters are
within the ratings specified by Sanken for the products.
Remarks About Using Thermal Silicone Grease
● When thermal silicone grease is used, it shall be applied evenly and thinly. If more silicone grease than required is
applied, it may produce excess stress.
● The thermal silicone grease that has been stored for a long period of time may cause cracks of the greases, and it
cause low radiation performance. In addition, the old grease may cause cracks in the resin mold when screwing the
products to a heatsink.
● Fully consider preventing foreign materials from entering into the thermal silicone grease. When foreign material is
immixed, radiation performance may be degraded or an insulation failure may occur due to a damaged insulating
plate.
● The thermal silicone greases that are recommended for the resin molded semiconductor should be used.
Our recommended thermal silicone grease is the following, and equivalent of these.
Type
Suppliers
G746
Shin-Etsu Chemical Co., Ltd.
YG6260 Momentive Performance Materials Japan LLC
SC102
Dow Corning Toray Co., Ltd.
Soldering
● When soldering the products, please be sure to minimize the working time, within the following limits:
260 ± 5 °C 10 ± 1 s (Flow, 2 times)
380 ± 10 °C 3.5 ± 0.5 s (Soldering iron, 1 time)
● Soldering should be at a distance of at least 1.5 mm from the body of the products.
Electrostatic Discharge
● When handling the products, the operator must be grounded. Grounded wrist straps worn should have at least 1MΩ
of resistance from the operator to ground to prevent shock hazard, and it should be placed near the operator.
● Workbenches where the products are handled should be grounded and be provided with conductive table and floor
mats.
● When using measuring equipment such as a curve tracer, the equipment should be grounded.
● When soldering the products, the head of soldering irons or the solder bath must be grounded in order to prevent leak
voltages generated by them from being applied to the products.
● The products should always be stored and transported in Sanken shipping containers or conductive containers, or be
wrapped in aluminum foil.
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
25
STR3A400 Series
IMPORTANT NOTES
● The contents in this document are subject to changes, for improvement and other purposes, without notice. Make sure
that this is the latest revision of the document before use.
● Application examples, operation examples and recommended examples described in this document are quoted for the
sole purpose of reference for the use of the products herein and Sanken can assume no responsibility for any
infringement of industrial property rights, intellectual property rights, life, body, property or any other rights of
Sanken or any third party which may result from its use.
● Unless otherwise agreed in writing by Sanken, Sanken makes no warranties of any kind, whether express or implied,
as to the products, including product merchantability, and fitness for a particular purpose and special environment,
and the information, including its accuracy, usefulness, and reliability, included in this document.
● Although Sanken undertakes to enhance the quality and reliability of its products, the occurrence of failure and defect
of semiconductor products at a certain rate is inevitable. Users of Sanken products are requested to take, at their own
risk, preventative measures including safety design of the equipment or systems against any possible injury, death,
fires or damages to the society due to device failure or malfunction.
● Sanken products listed in this document are designed and intended for the use as components in general purpose
electronic equipment or apparatus (home appliances, office equipment, telecommunication equipment, measuring
equipment, etc.).
When considering the use of Sanken products in the applications where higher reliability is required (transportation
equipment and its control systems, traffic signal control systems or equipment, fire/crime alarm systems, various
safety devices, etc.), and whenever long life expectancy is required even in general purpose electronic equipment or
apparatus, please contact your nearest Sanken sales representative to discuss, prior to the use of the products herein.
The use of Sanken products without the written consent of Sanken in the applications where extremely high
reliability is required (aerospace equipment, nuclear power control systems, life support systems, etc.) is strictly
prohibited.
● When using the products specified herein by either (i) combining other products or materials therewith or (ii)
physically, chemically or otherwise processing or treating the products, please duly consider all possible risks that
may result from all such uses in advance and proceed therewith at your own responsibility.
● Anti radioactive ray design is not considered for the products listed herein.
● Sanken assumes no responsibility for any troubles, such as dropping products caused during transportation out of
Sanken’s distribution network.
STR3A400-DSE Rev.2.1
SANKEN ELECTRIC CO.,LTD.
Sept. 18, 2015
http://www.sanken-ele.co.jp/en/
© SANKEN ELECTRIC CO.,LTD. 2014
26