STR4A100 Series Application Note

Off-Line PWM Controllers with Integrated Power MOSFET
STR4A100 Series
Application Note
General Descriptions
Package
The STR4A100 series are power ICs for switching
power supplies, incorporating a sense 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.
SOIC8
Not to Scale
Lineup
Features
 Auto Standby Function
No Load Power Consumption < 10mW
 Operation Mode
・Normal Operation ------------------------- PWM Mode
・Standby ------------------------ Burst Oscillation Mode
 Current Mode Type PWM Control
 Random Switching Function
 Slope Compensation Function
 Leading Edge Blanking Function
 Build-in Startup Circuit
 Bias Assist Function
 Soft Start Function
 Protections
Overcurrent Protection (OCP) --------- Pulse-by-Pulse
Overload Protection (OLP) ---------------- Auto-Restart
Overvoltage Protection (OVP) ------------ Auto-Restart
Thermal Shutdown Protection (TSD) ---- Auto-Restart
BR1
L2
D51
T1
VOUT
R1
C5
PC1
C1
P
S
R54
R51
R55
C51
D1
C4
R52
C53
C52 R53
8
6
7
U51
5
D2
R2
R56
S/GND S/GND S/GND S/GND
U1
STR4A100
FB/OLP VCC
1
C3
2
GND
D
C2
D/ST
4
 Electrical Characteristics
VD/ST(max.) = 730 V
Packages : D:DIP8, S:SOIC8
Products
fOSC(AVG)
RDS(ON)
(max.)
IDLIM(H)
65kHz
24.6 Ω
0.365 A
100kHz
12.9 Ω
0.485 A
STR4A162D
STR4A162S
STR4A164HD
 Output Power, POUT*
Adapter
Products
Open frame
AC230V
AC85
~265V
AC230V
AC85
~265V
STR4A162D
5.5 W
4.5 W
7.5 W
6W
STR4A162S
5W
4W
7W
5.5 W
STR4A164HD
9W
7W
13 W
10.5 W
* The output power is based on the thermal ratings, and the peak
Typical Application Circuit
VAC
DIP8
output power can be 120 to 140 % of the value stated here. At low
output voltage, small core and short ON Duty, the output power
may be less than the value stated here.
Applications
 White goods
 Auxiliary power for Flat TVs
 Low power AC/DC adapter
 Battery Chargers
 Other SMPS
PC1
STR4A100 - AN Rev.2.0
Jun. 25, 2013
C6
SANKEN ELECTRIC CO.,LTD.
1
STR4A100 Series
Application Note
CONTENTS
General Descriptions --------------------------------------------------------------------- 1
1. Absolute Maximum Ratings -------------------------------------------------------- 3
2. Recommended Operating Conditions -------------------------------------------- 3
3. Electrical Characteristics ----------------------------------------------------------- 4
4. Performance Curves ----------------------------------------------------------------- 6
5. Functional Block Diagram ---------------------------------------------------------- 7
6. Pin Configuration Definitions ------------------------------------------------------ 7
7. Typical Application Circuit -------------------------------------------------------- 8
8. Package Outline ---------------------------------------------------------------------- 8
9. Marking Diagram -------------------------------------------------------------------- 9
10. Operational Description ---------------------------------------------------------- 10
10.1 Startup Operation --------------------------------------------------------- 10
10.2 Undervoltage Lockout (UVLO) ----------------------------------------- 10
10.3 Bias Assist Function ------------------------------------------------------- 10
10.4 Soft Start Function -------------------------------------------------------- 11
10.5 Constant Output Voltage Control -------------------------------------- 11
10.6 Random Switching Function -------------------------------------------- 12
10.7 Automatic Standby Mode Function ------------------------------------ 12
10.8 Overcurrent Protection Function (OCP) ------------------------------ 12
10.9 Overvoltage Protection (OVP) ------------------------------------------ 13
10.10 Overload Protection Function (OLP) ---------------------------------- 13
10.11 Thermal Shutdown Function (TSD) ----------------------------------- 13
11. Design Notes ------------------------------------------------------------------------- 14
11.1 External Components ----------------------------------------------------- 14
11.2 PCB Trace Layout and Component Placement ---------------------- 15
12. Pattern Layout Example ---------------------------------------------------------- 17
13. Reference Design of Power Supply ---------------------------------------------- 18
OPERATING PRECAUTIONS ------------------------------------------------------ 20
IMPORTANT NOTES ----------------------------------------------------------------- 21
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
2
STR4A100 Series
Application Note
1. Absolute Maximum Ratings
 Refer to the datasheet of each product for these details.
 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
Characteristic
Symbol
Test Conditions
Pins
Rating
Units
Notes
FB/OLP Pin Voltage
VFB
1–5
−0.3 to 14
V
FB/OLP Pin Source Current
IFB
1–5
1.0
mA
VCC Pin Voltage
VCC
2–5
32
V
D/ST Pin Voltage
VD/ST
4–5
−0.3 to 730
V
−0.2 to 0.7
A
4A162D
−0.2 to 0.66
A
4A162S
−0.2 to 0.98
A
4A164HD
1.49
W
4A162D
1.34
W
4A162S
1.55
W
4A164HD
Drain Peak Current
Power Dissipation
Operating Ambient
Temperature
Storage Temperature
Junction Temperature
(1)
(2)
Positive: Single pulse
Negative: Within 2μs
of pulse width
IDP
(1)
4–5
–
(2)
PD
TOP
–
−40 to 125
°C
Tstg
–
−40 to 125
°C
Tj
–
150
°C
Refer to MOSFET Temperature versus Power Dissipation Curve
When embedding this hybrid IC onto the printed circuit board (cupper area in a 15mm×15mm)
2. Recommended Operating Conditions
Recommended operating conditions means the operation conditions maintained normal function shown in
electrical characteristics.
Rating
Characteristic
Symbol
Units
Min.
Max.
D/ST Pin Voltage in Operation
VD/ST(OP)
−0.3
584
V
VCC Pin Voltage in Operation
VCC(OP)
11
27
V
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
Notes
3
STR4A100 Series
Application Note
3. Electrical Characteristics
 Refer to the datasheet of each product for these details.
 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, VFB = 3 V, VD/ST = 10 V
Characteristic
Symbol
Power Supply Startup Operation
Operation Start Voltage
VCC(ON)
(1)
Operation Stop Voltage
VCC(OFF)
Circuit Current in
ICC(ON)
Operation
Startup Circuit Operation
VSTARTUP
Voltage
Startup Current
Startup Current Biasing
Threshold Voltage
PWM Operation
ISTARTUP
(1)
Average PWM Switching
Frequency
PWM Frequency
Modulation Deviation
Maximum ON Duty
VCC(BIAS)
Test
Conditions
Pins
Min.
Rating
Typ.
Max.
Units
Notes
VFB = 0 V
2−8
2−8
13.8
7.3
15.2
8.1
16.8
8.9
V
V
VCC = 12 V
2−8
―
―
2.5
mA
VFB = 0 V
VCC = 13.5 V
VFB = 0 V
VCC = 13.5 V
VD/ST = 100 V
8−3
19
29
39
V
2−8
−3.7
−2.1
−0.9
mA
VFB = 0 V
2−8
7.9
9.4
10.5
V
58
90
―
―
65
65
65
100
5
7
74
73
72
110
―
―
83
82
kHz
kHz
kHz
kHz
%
%
4A162D/S
―
290
―
ns
4A162D/S
―
250
―
ns
4A164HD
―
―
36
―
%
4−8
0.290
0.322
0.354
A
4−8
0.336
0.365
0.394
A
1−8
−120
−77
−45
µA
1−8
−28
−13
−6
µA
1−8
0.98
1.23
1.48
V
1−8
2−8
―
7.3
―
58
8.1
230
76
8.9
―
94
V
µA
ms
1−8
10.5
12.0
13.5
V
2−8
27.5
29.5
31.5
V
―
135
―
―
°C
―
―
70
―
°C
fOSC(AVG)
8−3
Δf
8−3
DMAX
8−3
tBW
―
4A164HD
4A162D/S
4A164HD
4A162D/S
4A164HD
Protection Function
Leading Edge Blanking
Time
(2)
Drain Current Limit
(2)
DDPC
Compensation ON Duty
Drain Current Limit
IDLIM(L)
(ON Duty = 0 %)
Drain Current Limit
IDLIM(H)
(ON Duty ≥ 36 %)
Maximum Feedback
IFB(MAX)
Current
Minimum Feedback
IFB(MIN)
Current
FB/OLP Pin Oscillation
VFB(OFF)
Stop Threshold Voltage
OLP Threshold Voltage
VFB(OLP)
OLP Operation Current
ICC(OLP)
OLP Delay Time
tOLP
FB/OLP Pin Clamp
VFB(CLAMP)
Voltage
OVP Threshold Voltage
VCC(OVP)
Thermal Shutdown
(2)
Tj(TSD)
Operating Temperature
Thermal Shutdown
(2)
Tj(TSDHYS)
Hysteresis
(1)
VCC(BIAS) > VCC(OFF) always.
(2)
Design assurance
STR4A100 - AN Rev.2.0
Jun. 25, 2013
VCC = 12 V
VFB = 0 V
VFB = 6.8 V
VFB = OPEN
VFB = OPEN
SANKEN ELECTRIC CO.,LTD.
4
STR4A100 Series
Application Note
Characteristic
Test
Conditions
Symbol
Pins
Min.
Ratings
Typ.
Max.
―
―
50
µA
―
―
―
21.0
11.0
―
24.6
12.9
250
Ω
Ω
ns
―
―
―
―
―
―
―
―
―
―
―
―
18
21
16
15
16
15
°C /W
°C /W
°C /W
°C /W
°C /W
°C /W
Units
Notes
MOSFET
Drain Leakage Current
IDSS
On Resistance
RDS(ON)
Switching Time
Ta = 125 °C
VFB = 0 V
VD/ST = 584 V
ID = 37 mA
ID = 52 mA
4−8
4−8
4−8
tf
4A162D/S
4A164HD
Thermal Characteristics
(3)
θj-F
―
(2)
Thermal Resistance
(4)
θj-C
―
4A162D
4A162S
4A164HD
4A162D
4A162S
4A164HD
(2)
Design assurance
(3)
Frame temperature (TF) measured at the root of the 7 pin(S/GND).
(4)
Case temperature (TC) measured at the center of the case top surface.
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
5
STR4A100 Series
Application Note
4. Performance Curves
 STR4A162D
Ambient Temperature versus
Power Dissipation Curve
Transient Thermal Resistance Curve
10
1.6
PD = 1.49 W
Transient Thermal Resistance
θj-c (°C /W)
Power Dissipation, PD (W)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1
0.1
0.01
0
25
50
75
100
125
1μ
1.0E-06
150
10μ
1.0E-05
100μ
1.0E-04
Ambient Temperature, TA (°C )
1m
1.0E-03
10m
1.0E-02
100m
1.0E-01
10m
1.0E-02
100m
1.0E-01
10m
1.0E-02
100m
1.0E-01
Time (s)
 STR4A162S
Ambient Temperature versus
Power Dissipation Curve
Transient Thermal Resistance Curve
1.6
10
PD = 1.34 W
1.2
Transient Thermal Resistance
θj-c (°C /W)
Power Dissipation, PD (W)
1.4
1
0.8
0.6
0.4
0.2
0
0
25
50
75
100 125 150
1
0.1
0.01
1μ
1.0E-06
10μ
1.0E-05
100μ
1.0E-04
Ambient Temperature, TA (°C )
1m
1.0E-03
Time (s)
 STR4A164HD
Ambient Temperature versus
Power Dissipation Curve
Transient Thermal Resistance Curve
1.8
10
PD = 1.55 W
Transient Thermal Resistance
θj-c (°C /W)
Power Dissipation, PD (W)
1.6
1.4
1.2
1
0.8
0.6
0.4
1
0.1
0.2
0
0
25
50
75
100 125 150
0.01
1μ
1.0E-06
10μ
1.0E-05
100μ
1.0E-04
Ambient Temperature, TA (°C )
STR4A100 - AN Rev.2.0
Jun. 25, 2013
1m
1.0E-03
Time (s)
SANKEN ELECTRIC CO.,LTD.
6
STR4A100 Series
Application Note
5. Functional Block Diagram
VCC
D/ST
2
1
4
5~8
FB/OLP
S/GND
6. Pin Configuration Definitions
FB/OLP
1
8
S/GND
VCC
2
7
S/GND
3
6
S/GND
D/ST
4
5
S/GND
Pin
Name
1
FB/OLP
2
VCC
3
―
4
D/ST
Descriptions
Input of constant voltage control signal and
input of OLP signal
Power supply voltage input for Control
Part and input of Overvoltage Protection
(OVP) signal
(Pin removed)
MOSFET Drain and input of startup
current
5
6
7
S/GND
MOSFET Source and ground
8
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
7
STR4A100 Series
Application Note
7. Typical Application Circuit
 The PCB traces S/GND pins should be as wide as possible, in order to enhance thermal dissipation.
 In applications having a power supply specified such that VDS 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/GND pin.
VAC
CRD clamp snubber
BR1
VOUT
R1
C5
C1
L2
D51
T1
PC1
C（RC）
Damper snubber
P
R55
C51
D1
S
C4
R54
R51
R52
C53
C52 R53
8
6
7
U51
5
D2
R2
R56
S/GND S/GND S/GND S/GND
U1
STR4A100
FB/OLP VCC
1
C3
2
GND
D
C2
D/ST
4
PC1
C6
Figure 7-1 Typical application circuit
8. Package Outline
 DIP8
NOTES:
1) All liner dimensions are in inches
2) Pb-free. Device composition compliant with
the RoHS directive
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
8
STR4A100 Series
Application Note
 SOIC8
Land Pattern Example (not to scale)
NOTES:
1) All liner dimensions are in inches
2) Pb-free. Device composition compliant with
the RoHS directive
1.6
(0.063)
3.8
(0.15)
1.27
(0.0500)
0.61
(0.024)
Unit : mm (inch)
9. Marking Diagram
8
4A1×××
Part Number (4A162D / 4A162S / 4A164HD)
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
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
9
STR4A100 Series
Application Note
10. 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).
10.1 Startup Operation
Figure10-2 shows the relationship of VCC pin voltage
and circuit current ICC. When VCC pin voltage decreases
to VCC(OFF) = 8.1 V, the control circuit stops operation by
UVLO (Undervoltage Lockout) circuit, and reverts to
the state before startup.
Circuit current, ICC
ICC（ON）
Figure 10-1 shows the circuit around VCC pin.
The IC incorporates the startup circuit. The circuit is
connected to D/ST pin. When D/ST pin voltage reaches
to Startup Circuit Operation Voltage VSTARTUP = 29 V,
the startup circuit starts operation.
During the startup process, the constant current,
ISTARTUP = −2.1 mA, charges C2 at VCC pin. When VCC
pin voltage increases to VCC(ON) = 15.2 V, the control
circuit starts switching operation.
During the IC operation, the voltage rectified the
auxiliary winding voltage, VD, of Figure 10-1 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 15 V to 20 V, taking account of the winding turns
of D winding so that VCC pin voltage becomes within
the specification of input and output voltage variation of
power supply.
VCC( BIAS) (max .)  VCC  VCC(OVP ) (min .)
⇒ 10.5(V)  VCC  27.5(V)
(1)
The startup time of IC is determined by C2 capacitor
value. The approximate startup time tSTART is calculated
as follows:
t START  C2 ×
10.2 Undervoltage Lockout (UVLO)
VCC( ON )－VCC( INT )
Stop
VCC（ON） VCC pin
voltage
VCC（OFF）
Figure10-2 Relationship between
VCC pin voltage and ICC
10.3 Bias Assist Function
Figure 10-3 shows VCC pin voltage behavior during
the startup period.
After VCC pin voltage increases to VCC(ON) = 15.2 V
at startup, the IC starts the operation. Then circuit
current increases and 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 VCC pin voltage.
VCC pin voltage
Startup success
IC starts operation
VCC(ON)
VCC(BIAS)
(2)
I STRATUP
Start
Target operating
voltage
Increase with rising of
output voltage
Bias assist period
VCC(OFF)
where,
tSTART : Startup time of IC (s)
VCC(INT) : Initial voltage on VCC pin
Startup failure
(V)
Time
T1
D1
Figure 10-3 VCC pin voltage during startup period
VAC
C1
4
D/ST
U1
VCC
2
D2
C2
S/GND
P
R2
VD
D
5~8
Figure 10-1 VCC pin peripheral circuit
STR4A100 - AN Rev.2.0
Jun. 25, 2013
The surge voltage is induced at output winding at
turning off a power MOSFET. When the output load is
light at startup, the surge voltage causes the unexpected
feedback control. This results the lowering of the output
power and VCC pin voltage. When the VCC pin voltage
decreases to VCC(OFF) = 8.1V, the IC stops switching
operation and a startup failure occurs. In order to prevent
this, the Bias Assist function is activated when the VCC
pin voltage decreases to the startup current threshold
biasing voltage, VCC(BIAS)= 9.4V. While the Bias Assist
function is activated, any decrease of the VCC pin
voltage is counteracted by providing the startup current,
SANKEN ELECTRIC CO.,LTD.
10
STR4A100 Series
Application Note
ISTARTUP, from the startup circuit. Thus, the VCC pin
voltage is kept almost constant.
By the Bias Assist function, the value of C2 is
allowed to be small and the startup time becomes shorter.
Also, because the increase of VCC pin voltage becomes
faster when the output runs with excess voltage, the
response time of the OVP function becomes shorter.
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.
10.4 Soft Start Function
Figure 10-4 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 6 ms.
during the soft start period, over current threshold is
increased step-wisely (5 steps). This function reduces
the voltage and the current stress of MOSFET and
secondary side rectifier diode.
Since the Leading Edge Blanking Function (refer to
Section 10.5 Constant Output Voltage Control) is
deactivated during the soft start period, there is the case
that ON time is less than the leading edge blanking time,
tBW = 290 ns.
After the soft start period, D/ST pin current, ID, is
limited by the Drain Current Limit, IDLIM, 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, tCCD ,
the output power is limited by the OLP protection
operation (OLP).
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 = 58 ms (min.).
provides the stable operation.
The FB/OLP pin voltage is internally added the slope
compensation at the feedback control (refer to Section
5.Functional 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 Figure10-5 and Figure10-6.
 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 ID decreases.
This control prevents the output voltage from
increasing.
 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.
STR4A100
FB Comp.
VROCP
FB/OLP
S/GND
1
VCC pin
voltage
ROCP
5~8
Startup of IC Startup of SMPS
Normal opertion
PC1
tSTART
C3
VCC(ON)
IFB
VCC(OFF)
Time
D/ST pin
current, ID
Figure10-5 FB/OLP pin peripheral circuit
Target voltage including
Slope Compensation
Soft start period
approximately 6 ms (fixed)
IDLIM
-
VSC
+
VROCP
tLIM < tOLP (min.)
Time
FB Comparator
Voltage on both
sides of ROCP
Figure 10-4 VCC and ID behavior during startup
Drain current,
ID
10.5 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
STR4A100 - AN Rev.2.0
Jun. 25, 2013
Figure10-6 Drain current, ID, and FB comparator
operation in steady operation
SANKEN ELECTRIC CO.,LTD.
11
STR4A100 Series
Application Note
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
10-7. 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 VSC, 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.
Target voltage
without Slope Compensation
because of periodic non-switching intervals.
Generally, 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.
If the VCC pin voltage decreases to VCC(BIAS)= 9.4 V
during the transition to the burst mode, the Bias Assist
function is activated and stabilizes the Standby mode
operation, because ISTARTUP 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
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 secondary winding and/or reducing the
value of R2 in Figure 11-2 (refer to Section 11.1
Peripheral Components for a detail of R2).
Output current,
IOUT
Burst oscillation
Below several kHz
tON1
t
Drain current,
ID
tON2
t
Normal
operation
t
Figure 10-7 Drain current, ID, waveform
in subharmonic oscillation
In the current mode control method, the FB
comparator and/or the OCP comparator may respond to
the surge voltage resulting from the drain surge current
in turning-on the power MOSFET. As a result, the
power MOSFET may turn off irregularly. In order to
prevent this response to the surge voltage in turning-on
the power MOSFET, the Leading Edge Blanking,
tBW= 290 ns, is built-in.
10.6 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.
10.7 Automatic Standby Mode Function
Automatic standby mode is activated automatically
when the drain current, ID, reduces under light load
conditions, at which ID is less than 20% to 25% of the
maximum drain current (it is in the Overcurrent
Protection state). The operation mode becomes burst
oscillation, as shown in Figure 10-8. Burst mode reduces
switching losses and improves power supply efficiency
STR4A100 - AN Rev.2.0
Jun. 25, 2013
Standby
operation
Normal
operation
Figure 10-8 Auto Standby mode timing
10.8 Overcurrent Protection Function (OCP)
Overcurrent Protection Function (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 Drain Current Limit.
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
actual drain peak current is, compared to the Drain
Current Limit. Thus, the peak current has some variation
depending on the AC input voltage in the drain current
limitation state.
In order to reduce the variation of peak current in the
drain current limitation state, the IC incorporates a
built-in Input Compensation function.
The Input Compensation function superposes a signal
with a constant slope (Figure10-9) into the internal
current detection signal and varies the internal threshold
voltage.
When AC input voltage is low (ON Duty is broad),
the Drain Current Limit after compensation increases.
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
SANKEN ELECTRIC CO.,LTD.
12
STR4A100 Series
Application Note
relation between the ON Duty and the drain current limit
after compensation IDLIM' is expressed as Equation (5).
When ON Duty is broader than 36 %, the drain current
limit becomes a constant value IDLIM(H).
I DLIM ' 
I DLIM( H )  I DLIM( L)
36(%)
 Duty  I DLIM( L )
(3)
Drain Current Limit after
compensation, IDLIM'
where,
Duty : MOSFET ON Duty (%)
IDLIM(H) : Drain current limit (ON Duty ≥ 36 %)
IDLIM(L) : Drain current limit (ON Duty = 0 %)
IDLIM(H)
IDLIM(L)
STR4A162
0.365 A
0.322 A
STR4A164
0.485 A
0.428 A
IDLIM(H)
IDLIM(L)
10.10 Overload Protection Function (OLP)
Figure10-10 shows the FB/OLP pin peripheral circuit,
and Figure10-11shows each waveform for OLP
operation.
When the peak drain current of ID is limited by OCP
operation, the output voltage, VOUT, decreases and the
feedback current from the secondary photo-coupler
becomes zero. Thus, the feedback current, IFB, charges
C3 connected to the FB/OLP pin and the FB/OLP pin
voltage increases. When the FB/OLP pin voltage
increases to VFB(OLP) = 8.1 V or more for the OLP delay
time, tOLP = 76 ms or more, the OLP function is
activated and the IC stops switching operation.
When the OLP function is activated, the Bias Assist
function is disabled. Thus the intermittent operation by
UVLO is repeated during OLP state. When the fault
condition is removed, the IC returns to normal operation
automatically.
U1
S/GND
FB/OLP
1
5~8
0
0%
2
D2 R2
PC1
74%
36%
ON Duty
VCC
C3
C2
Figure10-9 Relationship between ON Duty and Drain
Current Limit after compensation
Figure10-10 FB/OLP pin peripheral circuit
10.9 Overvoltage Protection (OVP)
When a voltage between VCC pin and S/GND
terminal increases to VCC(OVP) = 29.5 V or more, OVP
Function is activated and stops switching operation.
When OVP Function is activated, VCC pin voltage
decreases to Operation Stop Voltage VCC(OFF) = 8.1 V.
After that, the IC reverts to the initial state by UVLO
(Undervoltage Lockout) circuit, and the IC starts
operation when VCC pin voltage increases to
VCC(ON) = 15.2 V by Startup Current. Thus the
intermittent operation by UVLO is repeated in OVP
condition.
This intermittent operation reduces the stress of parts
such as power MOSFET and secondary side rectifier
diode. In addition, this operation reduces power
consumption because the switching period in this
intermittent operation is short compared with oscillation
stop period. When the abnormal condition is removed,
the IC returns to normal operation automatically.
In case the VCC pin voltage is provided by using
auxiliary winding of transformer, the overvoltage
conditions such as FB pin open can be detected because
the VCC pin voltage is proportional to FB pin voltage.
The approximate value of output voltage VOUT(OVP) in
OVP condition is calculated by using Equation (4).
VOUT(OVP) 
D
Output voltage in normal operation
×29.5V 
VCC pin voltage in normal operation
Non-switching interval
VCC pin voltage
VCC(ON)
VCC(OFF)
FB/OLP pin voltage
tOLP
VFB(OLP)
tOLP
Drain current,
ID
Figure10-11 OLP operational waveforms
10.11 Thermal Shutdown Function (TSD)
When the temperature of control circuit increases to
Tj(TSD) = 135 °C (min.) or more, Thermal Shutdown
function is activated and stops switching operation.
When the OLP function is activated, the Bias Assist
function is disabled. Thus the intermittent operation by
UVLO is repeated. When the temperature of the IC
decreases to Tj(TSD) − Tj(TSDHYS), the IC returns to normal
operation automatically.
(4)
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
13
STR4A100 Series
Application Note
11. Design Notes
11.1 External Components
Take care to use properly rated, including derating as
necessary and proper type of components.
 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.
 FB/OLP Pin Peripheral Circuit
Figure 11-1 performs high frequency noise rejection
and phase compensation, and should be connected
close to these pins. The value of C3 is recommended
to be about 2200p to 0.01µF, and should be selected
based on actual operation in the application.
T1
VAC
R1
C5
C1
C4
BR1
8
6
7
P
D1
5
S/GND S/GND S/GND S/GND
D2
R2
U1
C2
FB/OLP VCC
1
2
C3
D
D/ST
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 11-1). 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.
 D/ST Pin
Figure 11-3 shows D/ST pin peripheral circuit and
Figure 11-4 shows D/ST pin waveform in normal
operation.
The internal power MOSFET connected to D/ST pin
is permanently damaged when the D/ST pin voltage
and the current exceed the Absolute Maximum
Ratings. The D/ST pin voltage is tuned to be less than
about 90 % of the Absolute Maximum Ratings (657
V) in all condition of actual operation, and the value
of transformer and components should be selected
based on actual operation in the application. And the
D/ST pin voltage in normal operation is tuned to be
the Recommended Operating Conditions, VD/ST(OP) <
584 V.
The fast recovery diodes are recommended for using
as D1, D2 and D51. (for D1, SARS is also
recommended)
4
PC1
VAC
BR1
C5
Figure 11-1 The IC peripheral circuit
 VCC Pin Peripheral Circuit
The value of C2 in Figure 11-1 is generally
recommended to be 10µ to 47μF (refer to Section 10.1
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 11-2), and the
Overvoltage Protection function (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.
D51
T1
R1
C51
P
C1
D1
U1
S
4
D/ST
VCC
2
D2
R2
Control
C2
D
S/GND
5~8
Figure 11-3 D/ST pin peripheral circuit
D/ST pin voltage
< 657 V
VCC pin voltage
VD/ST(OP) < 584 V
Without R2
With R2
Time
Output current, IOUT
Figure 11-2 Variation of VCC pin voltage and power
STR4A100 - AN Rev.2.0
Jun. 25, 2013
Figure 11-4 D/ST pin voltage waveform
in normal operation
SANKEN ELECTRIC CO.,LTD.
14
STR4A100 Series
Application Note
 Phase Compensation
A typical phase compensation circuit with a
secondary shunt regulator (U51) is shown in Figure
11-5.
C52 and R53 are for phase compensation. The value
of C52 and R53 are recommended to be around
0.047μF to 0.47μF and 4.7 kΩ to 220 kΩ, respectively.
They should be selected based on actual operation in
the application.
L51
VOUT
D51
PC1
Margin tape
R55
C51
S
R54
R51
R52
C53
Bobbin
T1
auxiliary winding D from the primary windings P1
and P2.
where: P1 and P2 are windings divided the primary
winding into two.
▫ Winding structural example (b): Placing the
auxiliary winding D within the secondary-side
stabilized output winding, S1, in order to improve
the coupling of those windings.
where: S1 is a stabilized output winding of
secondary-side windings, controlled to constant
voltage.
P1 S1 P2 S2 D
P1、P2 ： Primary main winding
D
： Primary auxiliary winding
S1
： Secondary Stabilized
output winding
S2
： Secondary output winding
Margin tape
C52 R53
U51
Winding structural example (a)
R56
GND
Figure 11-5 Peripheral circuit around secondary shunt
regulator (U51)
 Transformer
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 about 3 to
4A/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.
Fluctuation of the VCC pin voltage by IOUT worsens
in the following cases, requiring a transformer
designer to pay close attention to the placement of
the auxiliary winding D:
▫ Poor coupling between the primary and secondary
windings (this causes high surge voltage and is seen
in a design with low output voltage and high output
current)
▫ Poor coupling between the auxiliary winding D and
the secondary stabilized output winding where the
output line voltage is controlled constant by the
output voltage feedback (this is susceptible to surge
voltage)
In order to reduce the influence of surge voltage on
the VCC pin, Figure11-6 shows winding structural
examples that are considered the placement of the
auxiliary winding D.
▫ Winding structural example (a): Separating the
STR4A100 - AN Rev.2.0
Jun. 25, 2013
Bobbin
Margin tape
P1 S1 D S2 S1 P2
Margin tape
Winding structural example (b)
Figure11-6 Winding structural examples
11.2 PCB Trace Layout and Component
Placement
PCB circuit trace design and component layout
significantly affects operation, EMI noise, and power
dissipation. Therefore, pay extra attention to these
designs. In general, trace loops shown in Figure11-7
where high frequency currents flow should be wide,
short, and small to reduce line impedance. In addition,
earth ground traces affect radiated EMI noise, and wide,
short traces should be taken into account.
Switch-mode power supplies consist of current traces
with high frequency and high voltage, and thus trace
design and component layouts should be done to comply
with all safety guidelines.
Furthermore, because the power MOSFET has a
positive thermal coefficient of RDS(ON), consider it when
preparing a thermal design.
Figure11-7 High frequency current loops
(hatched areas)
SANKEN ELECTRIC CO.,LTD.
15
STR4A100 Series
Application Note
Figure11-8shows the circuit design example.
 Secondary Rectifier Smoothing Circuit Trace Layout:
T1(winding S) to D51 to C51
This is the trace of the rectifier smoothing loop,
carrying the switching current, and thus it should be
as wide and short 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.
 IC Peripheral Circuit
(1) S/GND pin Trace Layout: S/GND pin to C1 to T1
(winding P) to D/ST pin
This is the main trace containing switching currents,
and thus it should be as wide and short as possible. If
C1 and the IC are distant from each other, placing a
capacitor such as film capacitor (about 0.1μF and
with proper voltage rating) close to the transformer
or the IC is recommended to reduce impedance of
the high frequency current loop.
(2) S/GND Pin Trace Layout: S/GND pin to C2(−) to
T1(winding D) to R2 to D2 to C2(+) to VCC pin
This is the trace for supplying power to the IC, and
thus it should be as wide and short as possible. If C2
and the IC are distant from each other, placing a
capacitor such as film capacitor (about 0.1μ to
1.0μF) close to the VCC pin and the GND pin is
recommended.
D51
T1
R1
C5
C1
P
C4
S
D1
8
6
7
C51
5
S/GND S/GND S/GND
NC S/GND
D2
R2
U1
STR4A100
D
C2
FB/OLP VCC
1
D/ST
2
Main power
circuit trace
4
GND trace for the IC
C3
PC1
C9
Secondary Rectifier
Smoothing Circuit
Trace
Figure11-8 Peripheral circuit example around the IC
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
16
STR4A100 Series
Application Note
12. Pattern Layout Example
The following show the PCB pattern layout example and the schematic of circuit using STR4A100 series (DIP8
type). Only the parts in the schematic are used. Other parts in PCB are leaved open.
Top view
Bottom view
Figure 12-1 PCB circuit trace layout example (DIP8 type)
F1
L1
L51
D50
T1
VOUT
VAC
R56
BR1
C3
C1
C51
R1
R51
C2
R54
PC1
R57
R53
R2
P1
C8
S1
R55
6
7
C53
D1
U50
8
C54
C52
R58
5
S/GND S/GND S/GND
NC S/GND
D2
R6
GND
U1
STR4A100
D
C4
FB/OLP VCC
1
C7
2
D/ST
4
PC1
C9
Figure 12-2 Circuit schematic for PCB circuit trace layout
The above circuit symbols correspond to these of Figure 12-1.
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
17
STR4A100 Series
Application Note
13. 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 voltage
Output current
STR4A162D
AC85V to AC265V
5 W (peak)
5V
1 A (max.)
 Circuit schematic
F1
L51
L1
D50
T1
VOUT
VAC
R56
BR1
C3
C1
R51
C51
R1
C2
R54
PC1
R57
R53
R2
P1
C8
8
6
7
C54
C52
S1
R55
C53
D1
U50
5
D2
S/GND S/GND S/GND
NC S/GND
R58
R6
U1
GND
STR4A100
D
C4
FB/OLP VCC
1
C7
2
D/ST
4
PC1
C9
 Bill of materials
Symbol
BR1
F1
L1
C1
(2)
C2
C3
C4
(2)
(2)
C7
C8
C9
R1
(3)
Part type
Recommended
Sanken Parts
Ratings(1)
Symbol
Part type
Ratings(1)
T1
Transformer
AC 250 V, 1 A
L51
Inductor
See
the specification
5 μH
470 μH
400 V, 10 μF
D50
C51
Schottky
Ceramic, chip
40 V, 2.5 A
50 V, 2200 pF
Electrolytic
Ceramic, chip
Electrolytic
400 V, 10 μF
2 kV, 1000 pF
50 V, 10 µF
C52
C53
C54
Electrolytic
Electrolytic
Electrolytic
10 V, 1000 µF
0.1 µF
10 V, 470 µF
Ceramic, chip
Ceramic, chip
Ceramic, Y1
Metal oxide,
chip
General, chip
General, chip
General, chip
4700 pF
Open
250 V, 2200 pF
R51
R53
R54
General, chip
General, chip
General, chip
22 Ω
220 Ω
1.5 kΩ
470 kΩ
R55
General, chip
33 kΩ
General, chip
600 V, 1 A
Fuse
CM inductor
Electrolytic
(2)
(2)
(2)
RK34
100 Ω
10 kΩ
10 kΩ
VREF = 2.5 V
D2
First recovery
200 V, 1 A
AL01Z
U50
Shunt regulator
TL431 or equiv
PC123
U1
IC
STR4A162D
PC1
Photo-coupler
or 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.
(2)
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 for that to reduce each applied voltage, according to the requirement of the application.
R2
R6
D1
(2)
STR4A100 - AN Rev.2.0
Jun. 25, 2013
47 Ω
2.2 Ω
SARS01
EM01A
Recommended
Sanken Parts
R56
R57
R58
(2)
General, chip
General, 1%
General, 1%
SANKEN ELECTRIC CO.,LTD.
18
STR4A100 Series
Application Note
 Transformer specification
▫ Primary inductance, LP
▫ Core size
▫ Al-value
▫ Winding specification
：2.2 mH
：EI-16
：119 nH/N2 (Center gap of about 0.3 mm)
Winding
Symbol
Number of
turns (T)
Wire diameter
(mm)
Construction
Primary winding
P1
136
φ 0.20
Four layers
Output winding
S1
8
φ 0.3 × 2
Single-layer
Auxiliary winding
D
21
φ 0.20
Single-layer
D
S1
VDC
P1
D/ST
P1
Enameled
Copper Wire
Triple insulated
wire
Enameled
Copper Wire
5V
S1
VCC
Bobbin
Core
Wire
GND
D
GND
●: Start at this pin
Cross-section view
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
19
STR4A100 Series
Application Note
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 Silicone Grease with a Heatsink
 When silicone grease is used in mounting the products on a heatsink, it shall be applied evenly and thinly. If more
silicone grease than required is applied, it may produce excess stress.
 Volatile-type silicone greases may crack after long periods of time, resulting in reduced heat radiation effect.
Silicone greases with low consistency (hard grease) may cause cracks in the mold resin when screwing the
products to a heatsink.
Our recommended silicone greases for heat radiation purposes, which will not cause any adverse effect on the
product life, are indicated below:
Type
Suppliers
G746
Shin-Etsu Chemical Co., Ltd.
YG6260 Momentive Performance Materials Inc.
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 (DIP8).
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.
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
20
STR4A100 Series
Application Note
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 and operation 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 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.
 The contents in this document must not be transcribed or copied without Sanken’s written consent.
STR4A100 - AN Rev.2.0
Jun. 25, 2013
SANKEN ELECTRIC CO.,LTD.
21