概述
规格参数
数据手册STR-L6452 概述
Switching Controller 开关式稳压器或控制器
STR-L6452 规格参数
| 生命周期： | Active | 包装说明： | , |
| Reach Compliance Code： | unknown | ECCN代码： | EAR99 |
| HTS代码： | 8542.39.00.01 | 风险等级： | 5.77 |
| 模拟集成电路 - 其他类型： | SWITCHING CONTROLLER | Base Number Matches： | 1 |
STR-L6452 数据手册
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PDF下载STR-L6400 APPLICATION NOTE
Ver. 1.4
STR-L6400 Series
Application Note (Ver. 1.4)
Sanken Electric Co., Ltd.
http://www.sanken-ele.co.jp
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.1
STR-L6400 APPLICATION NOTE
Ver. 1.4
/ / / / / / / / / / / / / / / / / Index / / / / / / / / / / / / / / / /
1. General Descriptions ·························································································3
2. Features and Production Lineup ·····································································3
3. Functional Block Diagram and Terminal List ················································4
4. Package Information ·························································································5
5. Electrical Characteristics ··················································································6～8
6. Typical Application Circuit ··············································································9
7. Functional Descriptions ····················································································10～26
7.1 VCC (No.6) Terminal ···················································································10～12
7.2 ADJ (No.10) Terminal ················································································13～16
7.3 FB (No.7) Terminal ·····················································································17～19
7.4 BD (No.8) Terminal ····················································································20～22
7.5 OCP (No.9) Terminal and Bottom-skip Operation ·································23～24
7.6 Standby Operation ······················································································25
7.7 Maximum ON Time Limitation Function ················································25
7.8 Phase Compensation ···················································································26
8. Design Notes ·······································································································27～28
/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
!WARNING!
● Sanken reserves the right to make changes without further notice to any products herein in the interest of improvements
in the performance, reliability, or manufacturability of its products.
Before placing order, Sanken advises its customers to obtain the latest version of the relevant information to verify that the
information being relied upon is current.
● Application and operation examples described in this application note are provided for a supplementary purpose only.
Conditions in actual use and variations in additional parts are not considered.
When using the products herein, the applicability and suitability of such products for the intended purpose or object shall be
reviewed at the user’s responsibility.
● Application and operation examples described in this application note are given for reference only and Sanken assumes 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.
● 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 society due to device failure or malfunction.
● This publication shall not be reproduced in whole or in part without prior written approval form Sanken.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.2
STR-L6400 APPLICATION NOTE
Ver. 1.4
1. General Descriptions
The STR-L6400 series devices comprise an integrated MOSFET and a multifunction controller chip for
quasi-resonant switching power supply applications.
In normal operation, the quasi-resonant operation mode coupled with the bottom-skip functions achieves high
efficiency and low noise. In standby operation, the burst operation mode ensures lower power consumption.
The controller circuit is common in the STR-Y6400 series, using the compact 7-pin full mold package
(TO220F-7L: Sanken designation: FMS207). The STR-L6400 series are using the SIP 10-pin type (Sanken
designation: STA-10), providing enough clearance and creepage isolation between high voltage terminals and
low voltage terminals. These switchers also provide various protection features that allow power supply designs
that are highly reliable and simple－with fewer peripheral components.
2. Features and Production Lineup
z SIP-10pin package
z Built-in Startup circuit (eliminates startup losses and results in low power consumption)
z Multi-mode control enables the high efficiency operation across the full load range
z Automatic Standby mode (improves efficiency by burst-oscillation at light loads,
Input wattage Pin < 0.1 W at zero output load condition)
z Bottom-skip mode reduces the switching loss under medium to light loads
z Built-in soft start function reduces the stress applied to power MOSFET during transitions
z Built-in Leading Edge Blanking (LEB) function
z Built-in protection functions for Overcurrent (OCP), Overvoltage (OVP), Overload (OLP), Thermal
shutdown (TSD) protection and maximum ON time limitation
z Two-chip structure: a MOSFET and a control IC (the MOSFET has an avalanche energy guarantee)
The production lineup for the STR-L6400 series provides the options shown in the following table.
MOSFET
RDS(ON)
DSS(MIN)[V] (MAX)[Ω]
Vin AC
[V]
Pout [W]
(Note 1,2)
Product No.
V
100
220
100
220
22
30
15
25
STR-L6452
STR-L6472
650
850
3.4
6.5
Note 1: The maximum output power is derived from thermal specifications. The actual output power may be
available around 120 – 140% of the above values, respectively, but will be limited by ON duty setting
on transformer design or lower output voltage.
Note 2: The condition of the maximum output power is “without heat sink”.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.3
STR-L6400 APPLICATION NOTE
Ver. 1.4
3. Functional Block Diagram and Terminal List
The devices share a common basic electrical configuration, as shown in the functional block diagram in fig.3.
The assignments of terminals in the packages also is common throughout the series, allowing easier design reuse.
The terminal assignments are shown in the Terminal List table in tab.3.
D/Startup
6
1
Startup
1-3
Vcc
UVLO
Reg/Iconst
DRV
5
7
S/GND
FB
Latch
OSC
Logic
FB/STB
OCP
9
8
OCP
BD
ADJ
10
BD
ADJ/SS
Fig.3 STR-L6400 Series Functional Block Diagram
Terminal List Table
Terminal
Symbol
Name
Descriptions
No.
1 - 3
5
6
D/Startup
S/GND
VCC
Drain / Start-up Terminal
Source / Ground Terminal
Power Supply Terminal
MOSFET Drain / Start-up current input
MOSFET Source / Ground
Input of power supply for control circuit
Constant voltage control signal input /
Standby control input / OLP signal input
7
FB
Feedback Terminal
Bottom Detection /
OCP Compensation for AC Input
Voltage Terminal
QR signal input /
Overcurrent compensation input
8
BD
OCP pulse input /
Bottom-skip signal input
Soft start control /
9
OCP
ADJ
OCP Input Terminal
10
Adjustment Terminal
Bottom-skip delay time control /
Remote ON/OFF signal input
Tab.3 STR-L6400 Series Terminal List table
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.4
STR-L6400 APPLICATION NOTE
Ver. 1.4
4. Package Information
SIP-10 pin type (Sanken designation: STA-10)
No.4 terminal is removed to provide greater clearance and creepage isolation for the high voltage input (No.1-3)
and No.3 terminal is cut.
The package dimensions and branding are shown below, and this lead framing number is LF437.
Dimensions in mm
a. Type Number
Material of terminal: Cu
b. Lot Number : YMDD
Treatment of terminal : Ni plating + solder dip
Weight: Approx. 2.8g
Y is the last digit of the year of manufacture
M is the month( 1 to 9, O,N,D)
DD is the 2-digit date
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.5
STR-L6400 APPLICATION NOTE
Ver. 1.4
5. Electrical Characteristics (Example: STR-L6472 )
The following tables provide electrical characteristics for the STR-L6400 series.
The STR-L6472 is used as an example.
Both absolute maximum ratings and operating characteristics are provided.
Certain details vary among the individual devices.
5.1 Absolute Maximum Ratings, valid at Ta = 25°C
Parameter
Terminal
1－5
Symbol
IDpeak
IDMAX
EAS
ILpeak
VCC
Rating
4.2
Unit
A
Note
Single pulse
1
※
Drain Current
1
※
Maximum Switching Current
1－5
4.2
40
1.9
32
A
mJ
A
Ta=-30～+125℃
Single pulse
VDD=99V, L=20mH
1
※
Avalanche Energy
1－5
Supply Voltage for Control Circuit
Startup Terminal Voltage
6－5
1－5
10－5
7－5
8－5
8－5
9－5
V
VSTARTUP -1.0～VDSS
V
ADJ Terminal Sink Current
FB Terminal Sink Current
BD Terminal Sink Current
BD Terminal Source Current
OCP Terminal Voltage
IADJ
IFB
3.0
8.0
mA
mA
mA
IBDIN
IBDOUT
VOCP
2.0
-2.0
mA
V
-1.5～+2.0
With infinite
heat sink
14.7
W
1
※
Power Dissipation in MOSFET
1－5
PD1
2.0
0.8
W
W
Without heat sink
Power Dissipation in Control Circuit
Internal Frame Temperature
in Operation
―
―
PD2
TF
℃
-30～+125
―
―
―
Top
Tstg
Tch
-30～+125
-40～+125
+150
℃
℃
℃
Operating Ambient Temperature
Storage Temperature
Channel Temperature
＊1 Refer to individual device datasheet for details; value differs among devices.
Current characteristics are defined based on IC as Sink:+, Source:－.
＊
5. 2 Electrical Characteristics in MOSFET, valid at Ta = 25°C
Rating
MIN TYP MAX
Parameter
Terminal Symbol
Unit
Note
1
※
Drain-source Voltage
Drain Leakage Current
ON Resistance
1 – 5
1 – 5
1 – 5
1 – 5
―
VDSS
IDSS
RDS(ON)
tf
850
―
―
―
―
―
―
2.4
―
V
µA
Ω
300
6.5
200
1
※
1
※
Switching Time
―
nS
1
※
Thermal Resistance
θch-F
―
3.1 ℃/Ｗ Channel to internal frame
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.6
STR-L6400 APPLICATION NOTE
Ver. 1.4
5.3 Control Circuit Electrical Characteristics,
valid at Ta = 25°C, VCC=20V, unless otherwise specified (or noted).
Rating
MIN TYP MAX
Parameter
Terminal Symbol
Unit
Power Supply Start-up Operation
Operation Start Voltage
6－5
6－5
6－5
6－5
1－5
6－5
6－5
1－5
10－5
10－5
10－5
VCC(ON)
VCC(OFF)
ICC(ON)
14.4
9.0
―
16.2
10.0
3.5
18.4
11.3
5.5
V
V
Operation Stop Voltage
Circuit Current in Operation
Circuit Current in Non-operation
Start-up Circuit Operation Voltage
Start-up Current
mA
µA
V
ICC(OFF)
―
10
50
VSTART(ON)
55
82
100
-0.5
ICC(STARTUP) -2.4
-1.4
mA
Start-up Current after OLP Operation
Oscillation Frequency
ICC(STARTOLP) -1.10 -0.50 -0.15 mA
fOSC
17.5
2.0
21.0
2.3
25.0
2.6
kHz
V
Soft Start Operation Stop Voltage
Soft Start Operation Charge Current
Power-off Threshold Voltage
VADJ(SS)
IADJ(SS)
-148
8.2
-110
9.4
-71
µA
V
VADJ(OFF)
10.8
Normal Operation
Bottom-skip Operation Threshold Voltage 1
Bottom-skip Operation Threshold Voltage 2
Bottom-skip Operation Threshold Voltage 3
Bottom-skip Operation Start Voltage
Bottom-skip State Detection Bias Current
BD Terminal Upper Clamp Voltage
BD Terminal Lower Clamp Voltage
QR Operation Threshold Voltage 1
QR Operation Threshold Voltage 2
Maximum Feedback Current
9－5
9－5
9－5
10－5
10－5
8－5
8－5
8－5
8－5
7－5
VOCP(BS1) -0.720 -0.668 -0.605
VOCP(BS2) -0.485 -0.435 -0.381
VOCP(BS3) -0.205 -0.145 -0.085
V
V
V
VADJ(BS)
IADJ(BS)
3.8
-27
―
4.3
-20
4.8
-13
―
V
µA
V
VBD(HC)
VBD(LC)
VBD(TH1)
VBD(TH2)
IFB(MAX)
6.3
―
-0.075
0.31
0.15
-225
―
V
0.12
0.01
-315
0.60
0.32
-135
V
V
µA
Standby Operation
Standby State Detection Voltage
Standby State Start Voltage
7－5
10－5
7－5
1－5
VFB(STBIN)
VADJ(STB)
VFB(STBOP)
TONL(MIN)
1.40
5.7
1.63
6.2
1.85
6.8
V
V
Standby Operation Threshold Voltage
0.80
0.98
1.00
1.62
1.25
2.19
V
Minimum TON period (Normal Operation)
Minimum TON period
(Input Compensation Operation)
µS
1－5
TONH(MIN)
0.54
0.98
1.40
µS
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.7
STR-L6400 APPLICATION NOTE
Parameter
Ver. 1.4
Rating
MIN TYP MAX
Terminal
Symbol
Unit
Protection Operation
Maximum TON period
1－5
1－5
TON(MAX)
TON(LEB)
31
-
36
41
-
µS
nS
Leading Edge Blanking Time
354
Over Current Detection Threshold Voltage
(Normal Operation)
Over Current Detection Threshold Voltage
(Input Compensation Operation)
OCP* Terminal Source Current
9－5
9－5
VOCP(H)
VOCP(L)
-0.975 -0.930 -0.875
-0.904 -0.780 -0.656
V
V
9－5
8－5
8－5
7－5
7－5
7－5
7－5
6－5
6－5
IOCP(O)
IBD(TH1)
IBD(TH2)
IFB(OLP)
-260
-575
-565
-27
-130
-500
-450
-20
-40
-425
-375
-13
µA
µA
µA
µA
V
Input Compensation Detection Threshold Current 1
Input Compensation Detection Threshold Current 2
OLP* Bias Current
OLP* Auto-restart Threshold Voltage
OLP* Latch-off Bias Current
VFB(OLPAUTO) 6.3
IFB(OLPLa.OFF) -1.5
VFB(OLPLa.OFF) 8.6
6.7
7.3
-1.0
9.6
-0.5
10.2
31.0
8.9
mA
V
OLP* Latch-off Threshold Voltage
OVP* Operation Voltage
VCC(OVP)
26.0
6.2
28.5
7.5
V
2
※
Latch Circuit Release Voltage
FB Terminal Maximum Voltage
in Feedback Operation
VCC(La.OFF)
V
7－5
VFB(MAX)
Tj(TSD)
4.90
135
5.45
6.00
V
Thermal Shut-down Temperature
―
‐
‐
℃
＊2 Latch circuit is activated by OLP, OVP and TSD functions.
＊
QR : Quasi-resonant, OCP : Overcurrent Protection, OVP : Overvoltage Protection,
OLP : Overload Protection
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.8
STR-L6400 APPLICATION NOTE
Ver. 1.4
6. Typical Application Circuit
The PCB traces from the D/ST terminals (No.1-2 ), shall be as wide as possible, in order to enhance thermal
dissipation.
L
L2
OUT
AC
Input
D2
R5
PC1
R7
R8
R9
N
C1
P
R10
C8
STR-L6400
C9
C7
S
R2
D1
C2
Z2
1～3
D/Startup
Z1
6
D
VCC
8
BD
R3
(RBD
)
GND
Cont.FB
7
C10
(C
V
)
10
ADJ
R4
OCP
9
S/GND
5
T1
C3 C4 C5 C6 PC1
R1
(ROCP
)
C11
Fig.6 STR-L6400 typical application circuit
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.9
STR-L6400 APPLICATION NOTE
Ver. 1.4
7. Functional Descriptions
7.1 VCC (No. 6) Terminal
VCC is the power supply terminal for control circuit.
7. 1. 1 Start-up Circuit
The startup circuit is connected to the drain terminals, D/Startup
(No.1-3). During the start-up process, the constant current
(ICC(STARTUP) = –1.4 mA typical) charges C2 at VCC terminal
(see fig.7-1), and when the startup voltage level (VCC(ON) = 16.2
V typical) is reached, the device starts switching operation.
Hence, the C2 value decides the duration of the startup period,
according to the following formula:
C1
P
1～3
R2
D1
6
D/Startup
VCC
STR-L6400
S/GND
C2
D
OCP
5
9
tSTART = C2× (VCC(ON) – VCC(INIT)) / ICC(STARTUP) --- (1)
where tSTART is the startup period, in s, and VCC(INIT) is the initial
voltage on VCC terminal, in V. C2 shall be 10 to 47 µF,
if it is a general power supply application.
R1
T1
Fig.7-1 VCC peripheral circuit
After switching operation begins, the startup circuit turns off
automatically, to zero its current consumption.
CC
I
3.5mA
(TYP)
Fig.7-2 shows the relationship of VCC and ICC.
When VCC terminal voltage reaches VCC(ON) , the device starts
normal operation and ICC increases. While the device is in
operation, if VCC terminal voltage decreases to the shutdown
voltage level (VCC(OFF) = 10.0V typical), the undervoltage
lockout (UVLO) circuit stops device operation, and the device
reverts to the state before startup.
10μA
(TYP)
CC
V
10.0V
(TYP)
16.2V
(TYP)
Fig.7-2 Relationship of VCC and ICC at
startup and shutdown
As shown in fig.7-3, when the start-up fails because VCC
terminal voltage drops below VCC(OFF) = 10.0V (TYP), it will
be necessary for C2 to use a larger capacitance. As a larger
capacitance causes a longer start-up time, it is necessary to
examine about the problems on actual operations.
CC
V
Conrol circuit operation start
Operation success
16.2V
(TYP)
10.0V
(TYP)
Start-up failure
time
7. 1. 2 Auxiliary Winding
After the device starts normal operation, the voltage from
auxiliary winding (D in fig.7-1) becomes a power source to the
device. The auxiliary winding voltage needs to be adjusted to
approximately 18V, taking into account the turns ratio of
Fig.7-3 VCC behavior at startup
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.10
STR-L6400 APPLICATION NOTE
Ver. 1.4
auxiliary winding D, so that VCC terminal voltage becomes:
VCC(OFF) = 11.3V(max) < VCC < VCC(OVP) = 26.0 V(min) --- (2)
within the limits for input and output deviation.
And the bottom point of VCC terminal voltage is recommended 12.5V or higher.
In actual power supply circuits, there are cases in which VCC voltage fluctuates in direct proportion to the output
of the SMPS (see fig.7-4). This happens because the circuit current of STR-L6400 series is small, and C2 is
charged to a peak by the transient surge voltage that is generated at the moment MOSFET turns off.
To alleviate C2 peak charging, lowering the influence on auxiliary winding D of the surge voltage from the
primary winding shall be accomplished. It is effective to add some value R2, of several ohms to several tenths of
an ohm, in series with D1 (see fig.7-1). The optimal value of R2 shall be determined using a transformer
matching the application, because the proportion of VCC voltage versus the transformer output voltage differs
according to transformer structural design.
The proportion of change between VCC voltage and the SMPS output voltage becomes worse if:
▪ the coupling between the primary winding and the secondary winding of transformer get worse, and/or
▪ the coupling between the auxiliary winding D and the stabilizing output winding (a winding of the circuit that
controls a constant voltage) gets worse.
Considering the above, extra attention is required for the winding location of auxiliary winding D. Fig.7-5 and
7-6 diagram alternative designs for the location of auxiliary winding D.
Fig.7-4 Effect of R2 (see fig.7-1) on the proportion of
VCC versus the SMPS output current
Fig.7-5 Auxiliary winding D
remote from primary winding Px
Fig.7-6 Auxiliary winding D
within a stabilizing output winding, S1
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.11
STR-L6400 APPLICATION NOTE
Ver. 1.4
7. 1. 3 Over Voltage Protection
When more than OVP threshold voltage of VCC(OVP) = 28.5 V (TYP) occurs between VCC terminal and GND
terminal, the OVP function starts operation. It shuts down the device with latch mode.
The OVP function can detect overvoltage on the transformer secondary output, because the normal VCC power
supply voltage, from the auxiliary winding of transformer, is in proportion to the output voltage.
This provides protection in cases such as a circuit open on the secondary side.
The secondary side output voltage that initiates OVP operation can be calculated approximately from the
following formula:
VOUT ( normal )[V ]
--- (3)
Vout(OVP) [V ]≒
× 28.5[V] (TYP )
VCC ( normal )[V ]
7. 1. 4 Latch Operation
The fault latch function prevents the device from normal switching while OVP, OLP, TSD protection functions
are in operation.
Fig.7-7 shows the transition diagram in OVP operation. When the device switching stops after a protection state
is latched, the VCC terminal voltage falls once to VCC(OFF) = 10.0V (TYP). After that, VCC terminal repeats the
charge and discharge between VCC(ON) = 16.2V (TYP) and VCC(OFF) = 10.0V (TYP) and prevents VCC voltage
excess increase.
Releasing the latch is done by dropping VCC voltage below VCC(La.Off) = 7.5V (TYP) (Latch Circuit Release Voltage),
which is normally done by shutting off AC input.
AC off
(Input electrolytic capacitor, C1, voltage falls)
OVP operation
28.5V
(TYP)
Keeping latch operation
16.2V
(TYP)
Available to re-start
10.0V
(TYP)
Latch circuit release voltage →
time
Fig.7-7 Transition diagram in OVP operation
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.12
STR-L6400 APPLICATION NOTE
Ver. 1.4
7.2 ADJ (No.10) Terminal
ADJ terminal has 5 functions as below.
① Soft start function
② Delay time setting for QR mode switching
③ Delay time setting for auto standby switching
④ Disabling bottom-skip function / Auto standby function
⑤ External ON /OFF control
7.2.1 Soft Start Function
The built-in soft start function reduces the voltage and current stresses to MOSFET and secondary diode, during
the start-up period. Fig.7-8 shows the peripheral circuit for ADJ terminal and the waveforms of MOSFET drain
current ID and ADJ terminal voltage VADJ
.
C3 between ADJ terminal and GND terminals is charged with IADJ(SS) = －110µA (TYP) (Soft Start Operation
Charge Current). The tON period of MOSFET is limited depending on the ADJ terminal voltage. The soft start
operation continues until the ADJ terminal voltage reaches VADJ(SS) = 2.3V(TYP) (Soft Start Operation Stop
Voltage). For reference, in case that C3 is 0.22µF, the soft start period is about 4.6ms (TYP).
VADJ
Soft start
period
VADJ(SSCP)= 2.9V(TYP)
|
STR-L6400
VADJ(SS)= 2.3V(TYP)
Charged with 110uA
ADJ
10
110uA
C3
S/GND
5
time
ID
OCP limit
time
Fig.7-8 ADJ terminal peripheral circuit / Soft start operation at start-up
VADJ(SSCP) is 2.9V (TYP) on the steady state condition.
7.2.2 Delay Time Setting for QR Mode Switching
STR-L6400 series has the delay time setting for the transit between QR and Bottom-skip mode, between
1 bottom-skip and 2 bottom-skip mode. Therefore, the operation in the same mode is available corresponding for
frequent dynamic load changes, and the reduction of audible noise from transformer is achieved with this
function. The delay time setting is adjusted using the charge time for soft start capacitor, C3, connected to ADJ
terminal as shown in fig.7-8.
Under the load change, only when OCP terminal voltage reaches VOCP(BSX) (Bottom-skip Operation Threshold
Voltage) and continues for a delay time, the operation mode is switched.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.13
STR-L6400 APPLICATION NOTE
Ver. 1.4
In case the load condition returns to the previous condition within a delay time, the operation mode is not
switched.
As VOCP(BSX) has hysteresis, the same mode is maintained with the hysteresis unless a load change exceeds
hysteresis.
V
ADJ
Charged with 20uA
The point detected
VADJ(BS)= 4.3V(TYP)
V
OCP(BSX)
V
ADJ(SSCP)= 2.9V(TYP)
STR-L6400
ADJ
10
20uA
C3
Delay time
S/GND
The fixed delay time in which C3 is
charged with 20uA from 2.9V to 4.3V.
5
time
1 bottom-skip operation
QR operation
The operation mode continues in the same mode
when VOCP(BSX)
detection is cancelled during the fixed delay time.
Fig.7-9 Transition diagram under dynamic load change / ADJ terminal peripheral circuit
When C3 is 0.22μF, the delay time is about 15.4mS.
7.2.3 Delay Time Setting for Auto Standby Switching
STR-L6400 series has the delay time setting for auto standby switching. It is also implemented in the same
manner of the delay time setting for QR mode switching in 7.2.2.
Fig.7-10 shows the transition diagram for the switching to auto standby operation.
ADJ
V
Charged with 110uA
ADJ(STB)= 6.2V(TYP)
V
Delay time
STR-L6400
ADJ
time
time
10
110uA
C3
FB
V
S/GND
5
VFB(STBIN)=1.63V(TYP)
V
FB(STBOP)
=1.00V(TYP)
2 bottom-skip operation
Standby operation
Fig.7-10 Transition diagram for the switching to auto standby operation
In case C3 is 0.22μF, the delay time is about 6.6mS.
When the load condition changes lighter from low load condition, the feedback current to FB terminal from the
photo-coupler is increasing, and the FB terminal voltage is decreasing. If FB terminal voltage falls below
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.14
STR-L6400 APPLICATION NOTE
Ver. 1.4
VFB(STBIN) = 1.63V (TYP) (Standby State Detection Voltage), C3 connected to ADJ terminal starts to be charged
with IADJ(SS) = 110µA (TYP) (Soft Start Operation Charging Current). When the ADJ terminal voltage reaches
VADJ(STB) = 6.2V (TYP) (Standby State Start Voltage), the device becomes ready to enter into the burst operation
mode. If the load becomes heavier again during the delay time and the FB terminal voltage exceeds VFB(STB)
=
1.63V (TYP), the device returns to the bottom-skip operation or the QR operation according to the load
conditions, without switching to the burst operation mode.
When the FB terminal voltage continues decreasing and falls below VFB(STBOP) = 1.0V (TYP) (Standby Operation
Threshold Voltage), the burst operation mode starts. In addition, when the TON period reaches TONL(MIN)* /
TONH(MIN)* = 1.62µS / 0.98µS (TYP) (Minimum TON period (Normal Operation) / (Minimum TON period (Input
Compensation Operation), the feedback current is increasing higher. Therefore, the minimum TON period works
for the trigger to enter to standby mode.
The burst operation mode cycle varies on the feedback current according to the load conditions.
※ TONL(MIN)* / TONH(MIN)*: Actual Ton period to standby mode depends on input compensation: refer to 7.4.2.
7.2.4 Disabling Bottom-skip Function / Auto Standby Function
The bottom-skip function and the auto standby function are disabled by connecting external components to
ADJ terminal.
Fig.7-11 shows the circuit example for disabling both functions, and fig.7-12 shows only for disabling the auto
standby function.
110uA
20uA
10
STR-L6400
STR-L6400
ADJ
ADJ
10
D3
C3
R10
C3
S/GND
5
S/GND
5
A zener diode of Vz= 5.6V
A resistor of around 100kΩ
Fig.7-11 Circuit disabling both functions
of bottom-skip and auto standby
Fig.7-12 Circuit disabling only auto standby
function
Disabling Bottom-skip Function
During bottom-skip operation, the ADJ terminal charges C3 with IADJ(BS) = －20µA (TYP) (Bottom-skip State
Detection Bias Current). By connecting a resistor, R10, in parallel with C3 and limiting the terminal voltage
increase, the bottom-skip function is disabled. As shown in fig.7-11, by connecting R10 of around 100KΩ, the
bottom-skip function is disabled because ADJ terminal voltage is limited at 2V (= 20µA × 100kΩ), which is
lower than VADJ(BS) = 3.8V (MIN) (Bottom-skip Operation Start Voltage).
Disabling Auto Standby Function
To start the burst operation mode, the ADJ terminal voltage shall reach higher than VADJ(STB) = 6.2V (TYP).
However, by connecting a zener diode of VZ = 5.6V, D3, in parallel with C3, the auto standby function is
disabled because ADJ terminal voltage is limited under VADJ(STB) = 6.2V (TYP). In this case, the voltage
difference between VZ = 5.6V and VADJ(BS) = 4.3V (TYP) is not enough. It is necessary to take care of the zener
voltage accuracy and select the proper zener diode rank.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.15
STR-L6400 APPLICATION NOTE
Ver. 1.4
7.2.5 External ON / OFF Control
The ADJ terminal has the remote ON / OFF control function by applying the external signal. By increasing ADJ
terminal voltage to VADJ(OFF) = 9.4V (TYP) (Power-off Threshold Voltage) and over, the device is stopped (OFF).
Fig.7-13 shows the typical circuit example, the external power supply (12－16V) provides ADJ terminal with
more than VADJ(OFF) through R11 (10k – 30KΩ) and a photo-coupler when the photo-coupler turns on by the
external signal. And also by continuing to apply the higher voltage than VADJ(OFF), the device holds OFF state.
In this example, if the ON state is activated from the OFF state by turning off the photo-coupler, the operation
always starts from discharging the soft start capacitor. As a result, when the ON signal is applied, the ON state
begins after the soft start period.
External power supply
For example, 12～16V
V
ADJ
R11
For example,
10k～33kΩ
VADJ(OFF) = 9.4V(TYP)
VADJ(SSCP)= 2.9V(TYP)
PC2
time
ON
STR-L6400
ON
OFF
ADJ
10
I
D
C3
S/GND
5
time
Fig.7-13 Typical circuit for external ON / OFF control
On the circuit design like the above, as the maximum rating of ADJ terminal sink current is = 3.0mA (MAX), the
R11 value shall be calculated using the external power supply voltage and ADJ terminal current(below 3mA).
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.16
STR-L6400 APPLICATION NOTE
Ver. 1.4
7.3 FB (No. 7) Terminal
FB terminal has 3 functions:
① Output voltage control
② Overload protection (OLP)
③ Burst operation control for standby mode ⇒ Refer 7.6 Standby Operation
7.3.1 Constant Output Voltage Control
The constant output voltage control is achieved by connecting a photo-coupler to FB terminal and sinking the
feedback current. Fig.7-14 shows the peripheral circuit of FB terminal. As the maximum feedback current,
IFB(MAX), is –315µA (MIN), the forward current of photo-coupler on secondary side shall be set in consideration
of aging degradation of CTR(Current Transfer Ratio) and others.
phase compensation
Normal setting (OLP: Latch shutdown)
STR-L6400
FB
7
PC1
R4
S/GND
5
C5
C6
CR for OLP latch delay timing setting
Vz=8.2V
Option 1 (OLP: Auto restart)
phase compensation
STR-L6400
FB
7
PC1
R4
C5
S/GND
5
C6
D4
CR for OLP latch delay timing setting
220kΩ
Option 2 (OLP: Disabling both functions)
phase compensation
STR-L6400
FB
7
PC1
S/GND
5
R12
C6
Fig.7-14 FB terminal peripheral circuit / OLP operation mode selection
＊As for the values of resistance (R4) and capacitance (C5) for latch delay, generally, around 47kΩ and
4.7µF-10µF are recommended, respectively. The OLP function shall not activate on transient condition
(power on and power off), but activate on overload condition. The delay time for OLP shall be adjusted by
C5 value when it is shorter.
＊The capacitance (C6) for phase compensation shall be adjusted in the range of 470pF to 0.022µF. (Refer to
7.8, for the detail.)
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.17
STR-L6400 APPLICATION NOTE
Ver. 1.4
7.3.2 Overload Protection (OLP) Function
Fig.7-15 shows the transition diagram in OLP operation. When the secondary output is in overload and the
overcurrent protection function is activated on primary side, the output voltage decreases. As a result, the
secondary error amplifies is cut-off and the feedback current from the photo-coupler is eliminated. At this time,
the FB terminal is charged with IFB(OLP) = －20µA (TYP) (OLP Bias Current) during the latch delay time. If the
FB terminal voltage reaches VFB(OLPAUTO) = 6.7V (TYP) (OLP Auto-restart Threshold Voltage), the OLP
function starts and the oscillation stops. During this period, the VCC terminal voltage decreases. However, after
the FB terminal voltage reaches VFB(OLPAUTO) = 6.7V (TYP), the internal bias is switched to IFB(OLPLa.OFF)
=
－1.0mA(TYP) (OLP Latch-off Bias Current). As a result, the FB terminal voltage rapidly reaches VFB(OLPLa.OFF)
= 9.6V (TYP) (OLP Latch-off Threshold Voltage) and the device enters into the latch mode, before VCC
terminal voltage falls below VCC(OFF) = 10.0V (TYP) (Operation Stop Voltage). The typical circuit of this
operation is shown in the normal setting (OLP: Latch Shutdown) in fig.7-14.
Latch shutdown
VFB
9.6V(TYP)
VFB(OLPLa.OFF)
Charged with -1.0mA(TYP)
in VFB
> 6.7V(TYP)
VFB(OLPAUTO)
ΔV
Charged with
-20μA(TYP)
tdly
VFB(MAX)
time
Fig.7-15 Transition diagram in OLP operation
There is the relative relation between VFB(OLPAUTO) and VFB(MAX), and the difference voltage, ΔV, between them
is around 1V verified by design.
The tdly charged with －20μA can be calculated approximately from the following formula:
1V × C5
--- (4)
tdly ≒
20uA
7.3.2-1 Overload Protection (OLP) Function with Auto-restart
The transition diagram of OLP function with auto-restart is shown in fig.7-16. The circuit in "Option 1" in
fig.7-14 is for this function with auto-restart. A zener diode of VZ = 8.2V, D4, is placed between FB terminal and
GND terminal, limiting FB terminal voltage not to reach VFB(OLPLa.OFF) = 9.6V (TYP).
As a result, the intermittent operation starts under the overload condition.
When the overload condition is released, the auto-restart is available. As shown in fig.7-16, after the FB terminal
voltage reaches VFB(OLPAUTO) = 6.7V (TYP), the oscillation stops. Then the VCC terminal voltage decreases and
the auto-restart operation starts. In this operation, as the start-up current decreases to ICC(STARTOLP) = －0.5mA
(TYP) (Start-up Current after OLP Operation), the oscillation stop period is extended and the heat generation at
switching elements is reduced.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.18
STR-L6400 APPLICATION NOTE
Ver. 1.4
As ICC decreases to ICC(STARTOLP)
the OFF period is extended.
,
time
Reduce the start-up current to ICC(STARTOLP)
Fig.7-16 Transition diagram in auto-restart operation
7.3.2-2 Disabling OLP Function
The circuit in "Option 2" in fig.7-14 is for disabling OLP function. When R12 (220KΩ or lower ) is placed
between FB terminal and GND terminal, IFB(OLP) = －20µA (TYP) (OLP Bias Current) flows through R12, and
the FB terminal voltage does not reach VFB(OLPAUTO) = 6.7V (TYP). Then the OLP functions (both of the latch
operation and the auto-restart operation) are disabled.
When the OLP function is disabled, the output characteristics shall be constant power.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.19
STR-L6400 APPLICATION NOTE
Ver. 1.4
7.4 BD (No 8) Terminal
BD terminal has two separated functions.
① Turn-on timing determination by flyback voltage (plus voltage) of auxiliary winding
② Input compensation by forward voltage (minus voltage) of auxiliary winding
7. 4. 1 Bottom-on Timing (QR Signal)
The bottom-on function* is maintained, not only in the QR mode, but else in the bottom-skip mode.
※Bottom-on Function*: To reduce the switching losses at MOSFET turn-on, by turning-on at each bottom
point of VDS waveform of MOSFET.
Fig.7-17 shows the peripheral circuit for BD terminal and auxiliary winding voltage. After limiting the current of plus
side (fly-back side) waveform generated on auxiliary winding by R3(RBD), the plus side voltage is input to BD
terminal.
T1
D1
R2
Flyback voltage
R3
C2
D
)
(
BD
R
Plus side
O V
Forward voltage
8
Minus side
BD
STR-L6400
S/GND
ON
T
5
Waveform of auxiliary winding
Fig.7-17 BD terminal peripheral circuit and auxiliary winding voltage
By clamping BD terminal voltage internally, the voltage shown in fig.7-18 (example: QR mode under heavy
load) is input to BD terminal. During this voltage is input, MOSFET TOFF period continues. After that, the BD
terminal voltage falls.
When the falling is detected at VBD(TH2) = 0.15V (TYP) (Quasi-resonant Operation Threshold Voltage 2),
MOSFET is turned-on. After the detection of the falling, the BD terminal threshold voltage is set to VBD(TH1)
0.31V (TYP) (Quasi-resonant Operation Threshold Voltage 1), to prevent malfunctions.
=
Unfavorable waveform
Normal waveform
= 6.3V(TYP)
= 0.31V(TYP)
V
BD(HC)
= 6.3V(TYP)
BD(HC)
V
V
V
BD(TH1)
= 0.31V(TYP)
= 0.15V(TYP)
VBD(TH1)
= 0.15V(TYP)
BD(TH2)
BD(TH2)
0V
V
0V
BD terminal
blanking time 1.0uS(TYP)
Fig.7-19 BD terminal voltage
using a poor coupling transformer
Fig.7-18 BD terminal voltage in QR operation
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.20
STR-L6400 APPLICATION NOTE
Ver. 1.4
Fig.7-19 shows the BD terminal waveform using a transformer with poor coupling. For example, if the turn ratio
(P/S) of primary and secondary winding is large (such as in the low-voltage and high current output
specifications), a surge voltage may be generated on BD terminal voltage through auxiliary winding at MOSFET
turning-off.
As BD terminal blanking time (1.0μS(TYP)) is implemented, the QR signal is not detected during this time.
If the surge is applied beyond the blanking time, the MOSFET may be switched with high frequency by the
detection of ringing voltage as the QR signal. In this case, the MOSFET loss shall be excessive. If the channel
temperature exceeds the maximum rating, the MOSFET destruction is caused. When the high frequency
operation occurs, it is necessary to examine the pattern layout (between BD terminal and GND terminal),
the transformer design (structure of primary – secondary windings and position of auxiliary winding),
the snubber circuit adjustment, the probe position of oscilloscope and others.
Due to the inherent delay at BD terminal, if R3(RBD) value is too large, the turn-on timing shall be delayed as
shown in fig.7-20.
As R3(RBD) value is relating to the input compensation of overcurrent protection (OCP) and the input
compensation of standby, R3(RBD) value shall be adjusted on actual operations referring the following 7.4.2.
Turn-on timing is delayed
VDS
VDS
Bottom point
Bottom point
ID
ID
The turn-on timing is delayed from the bottom
point of VDS waveform due to a large RBD
The ideal “bottom-on”: the turn-on timing is
at the bottom point of VDS waveform.
.
Fig.7-20 Waveform Examples at Bottom Point with / without Delay
7. 4. 2 OCP Input Compensation / Standby Input Compensation by R3(RBD
)
The switching between VOCP(H) / VOCP(L) (Over Current Detection Threshold Voltage), between TONH(MIN)
/
TONL(MIN) (Minimum TON period) (threshold for standby operation) is achieved by detecting the current which is
determined by forward voltage of auxiliary winding and R3(RBD).
The switching is done using the same detection threshold value of IBD(TH1) = －500µA (TYP) (Input
Compensation Detection Threshold Current 1).
7.4.2-1 OCP Input Compensation
When the QR mode converter is used in a universal input voltage range, the peak drain current varies because
the operating frequency and the input voltage vary (The drain peak current decreases in the higher input voltage
range.)
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.21
STR-L6400 APPLICATION NOTE
Ver. 1.4
As the value of OCP detection resistor, R1 (ROCP), is fixed, the above influence causes that the OCP operation
point shifts to the more overload side in the higher input voltage range. Comparing with the OCP operation point,
which is adjusted under the condition of the minimum input voltage of AC100V range and the maximum load,
the operation point in AC230V range shall shift around double. To suppress this phenomenon, the OCP threshold
voltage is possible to be switched, by sinking the current more than 500µA (TYP) from BD terminal through R3
(RBD) during the TON period, using the forward (minus) voltage of auxiliary winding shown in fig.7-17.
The OCP threshold voltage is switched as shown below:
① VOCP(H): －0.930V (TYP)
② VOCP(L): －0.780V (TYP)
when the current through RBD is below 500µA (TYP) during TON period
when the current through RBD is above 500µA (TYP) during TON period
＊On usual R3(RBD) design, the OCP operation point shall be VOCP(H) in AC100V input range, and VOCP(L)
in AC230V input range.
[Reference Example]
In case of: AC85V - AC264V universal input, 15V / 20W output QR mode converter
･Transformer winding: Np: 110T (Lp = 3.34mH), NS (15V): 9T
・Auxiliary winding D: 10T (equivalent to 18V)
・For input compensation around AC160V, the forward voltage is;
160 2 ×
(
10T /110 T = 20.57V
)
・To flow 500µA at 20.57V,
R3(RBD)= 20.57V / 500µA= 41.14kΩ → 39kΩ shall be selected in the E12 / E24 series (Although the
impedance between BD terminal and GND terminal gives influence actually, the approximate value shall be
calculated.)
・The maximum absolute rating of BD terminal is ±2mA. When R3(RBD) is 39kΩ, the current at the minus
side on the auxiliary winding voltage in fig.7-17 is －870µA at maximum input voltage, and the current at the
plus side is 300µA because of 18V output (auxiliary winding voltage ) and 6.3V (BD terminal clamp voltage).
Both of them are confirmed to be within the above range.
7.4.2-2 Standby Input Compensation
As described in 7.2.3, the minimum TON period works for the trigger to enter to standby mode.
For universal input operation, the TON period at entering to standby shall be largely different depending on the
input conditions. Even if the auto standby is achieved in AC230V input range, the auto standby shall not
achieved due to the wider TON period in AC100V input range, under the same load conditions.
In order to prevent this phenomenon, the minimum TON period compensation for entering to standby is
implemented.
For universal input design, it is recommended the compensation shall be effective around AC140 – AC160V.
Under the load condition to change the mode like standby ⇔ 2 bottom-skip, the TON period shall be detected to
be the following width, in addition to the conditions described in 7.2.3.
① TONL(MIN): 1.62µs when the current through RBD is below 500µA (TYP) during TON period
--- AC100V input range
② TONH(MIN): 0.98µs when the current through RBD is above 500µA (TYP) during TON period
--- AC230V input range
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.22
STR-L6400 APPLICATION NOTE
Ver. 1.4
7. 5 OCP (No. 9) Terminal and Bottom-skip Operation
7.5.1 Connection of OCP Terminal
The Overcurrent Protection (OCP) circuit detects each drain peak current level (on a pulse-by-pulse basis) of
MOSFET with a OCP detection resistor, R1 (ROCP), and limits the output power of the power supply.
The external circuit is shown in fig.7-21.
At the OCP detection, the leading edge blanking (LEB) function works. During TON(LEB) = 354ns (TYP)
(Leading Edge Blanking Time), the OCP detection is disabled preventing the unstable oscillations.
When coupling capacitance of transformer, drain voltage at MOSFET turning-on, resonance capacitor are higher
or the bottom detection is improper, the surge current at MOSFET turning-on may occur like the right side in
fig.7-22. If the surge voltage of turn-on portion, which is beyond TON(LEB) = 354ns (TYP), reaches the OCP
terminal voltage (the control value) determined by FB terminal voltage, the oscillation may be unstable.
When this phenomena occurs, an external filter with a resistor and a capacitor shown on the lower side in
fig.7-21 is recommended. In case of a larger filter resistor, the overcurrent may vary largely, due to the influence
of IOCP(O) = －130µA (TYP) (OCP Terminal Source Current) and longer response time. Considering the above,
the recommended values are approximately 100Ω and 220pF, respectively.
Generally, a filter circuit is unnecessary,
STR-L6400
because of the implemented LEB.
S/GND
5
OCP
9
R1
A filter circuit is recommended in case LEB does not work properly due
to a higher surge current at turn-on.
STR-L6400
S/GND
5
OCP
9
around 220pF
around 100Ω
R1
Fig.7-21 Typical examples for OCP terminal peripheral circuit
VOCP
VOCP
Surge voltage on R1(ROCP)generated by
surge current at turn-on
TON(LEB)
In case of small influence of surge
voltage at turn-on
In case of large influence of surge
voltage at turn-on
Fig.7-22 Waveforms of OCP Terminal Voltage
Page.23
Copy Right: SANKEN ELECTRIC CO., LTD.
STR-L6400 APPLICATION NOTE
Ver. 1.4
7.5.2 Bottom-skip Operation
The bottom-skip operation with multi-mode control is available.
The function is to switch between QR operation (under heavy load) and bottom-skip operation (under middle or
light load) according to the secondary load condition by detecting the drain current (actually OCP terminal
voltage).
Fig.7-23 and 7-24 show the transition diagrams from no load to heavy load, from heavy load to no load,
respectively. The multi-mode control changes the modes like standby mode ⇔ 2-bottom-skip mode ⇔
1-Bottom-skip mode ⇔ QR mode.
In actual operations, there are delay time settings for rapid load changes described in 7.2.2 and 7.2.3. However,
fig.7-23 and 7-24 are shown just the conceptual diagrams, and such delays are omitted.
VOCP(BS2)
-0.435V
VOCP(BS1)
-0.668V
VOCP(L)
-0.78V
Standby
No load
2 Skip
1 Skip
QR
Heavy load
Fig.7-23 Transition diagram from no load to heavy load
VFB(STBOP) = 1V,
TON = TONL(MIN) or TONH(MIN)
VOCP(BS2)
-0.435V
VOCP(BS3)
-0.145V
VOCP(L)
-0.78V
1 Skip
2 Skip
QR
Standby
Heavy load
No load
Fig.7-24 Transition diagram from heavy load to no load
As the hysteresis is implemented for each mode
switching of the increasing / decreasing load transitions,
the oscillation is stable near the switching thresholds
and the mode switching is achieved stably.
Fig.7-25 shows the switching hysteresis for each mode
switching.
Fig.7-25 Hysteresis for each mode switching
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.24
STR-L6400 APPLICATION NOTE
Ver. 1.4
7.6 Standby Operation
FB Terminal Voltage during Standby
As described in 7.2.3, the conditions for entering to standby mode are:
zWhen the ADJ terminal voltage reaches VADJ(STB) = 6.2V (TYP) (Standby State Start Voltage), the device
becomes ready to enter into the burst operation.
zWhen the FB terminal voltage falls below VFB(STBOP) = 1.0V (TYP) (Standby Operation Threshold Voltage),
the burst operation mode starts.
Under light load condition, when the TON period reaches TONL(MIN)/ TONH(MIN) = 1.62µS / 0.98µS (TYP)
(Minimum TON period (Normal Operation) / (Minimum TON period (Input Compensation Operation),
the feedback current is increasing higher. Therefore, the minimum TON period works for the trigger to enter to
standby mode.
As described in 7.4.2-2, when the input compensation is effective, the minimum TON period shall be
automatically switched; TONL(MIN) = 1.64µS (TYP) in AC100V input range or 0.98µS (TYP) in AC230V input
range.
Fig.7-26 shows the standby operation. During the standby operation, the burst operation mode repeats between
oscillation-stop mode and 2-bottom-skip mode.
In the burst operation mode, the energy supply from auxiliary winding synchronizes with the energy supply to
the output. As a result, the ripple may be generated on VCC terminal voltage due to burst operation. If the VCC
terminal voltage falls below VCC(OFF) = 11.3V (MAX) (Operation Stop Voltage), some adjustments, such as
increasing the C2 value between VCC terminal and S /GND terminal, are necessary to stabilize the VCC terminal
voltage.
VCC
↑UVLO: VCC(OFF)= 11.3V(MAX)
time
Non-oscillation
period
Non-oscillation
period
ID
Oscillation period →
Oscillation period →
time
Fig.7-26 Waveform in Standby Operation
7.7 Maximum ON Time Limitation Function
During low input voltage or the transition operation
such as power supply ON/OFF, the maximum TON
period is limited to be TON(MAX) = 36µsec (TYP)
(Maximum TON period) (refer to fig.7-27).
Maximum On time
ID
VDS
On the power supply design, the confirmation about
MOSFET TON period is necessary, under the condition
with minimum input voltage and maximum load
condition.
time
Fig.7-27 Maximum TON period confirmation
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.25
STR-L6400 APPLICATION NOTE
Ver. 1.4
7.8 Phase Compensation
Fig.7-28 shows the circuit diagram for the secondary error amplifier, using a general shunt regulator. As for
the phase compensation capacitor, C8, the capacitance shall be adjusted in the range of 0.047 – 0.47µF, and
finally determined on actual operations.
In case the load specification is not general, the phase compensation on secondary error amplifier is not
enough due to the larger ripples on rectifier capacitor, or the operation is not stable due to the noises to FB
terminal, it is recommended to place a capacitor, C6, between FB terminal and GND terminal shown in
fig.7-29. As for C6, the capacitance shall be adjusted in the range of 470pF to 0.022µF and finally determined
on actual operations.
L2
PC1
T1
OUTPUT
C9
phase compensation
R5
D2
STR-L6400
R8
R9
FB
7
PC1
R4
C5
R7
S/GND
5
C8
S
C6
C7
R10
Z2
CR for OLP latch delay timing setting
Normal setting (OLP: Latch shutdown)
GND
Fig.7-28 Peripheral circuit
around secondary shunt regulator
Fig.7-29 FB terminal peripheral circuit
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.26
STR-L6400 APPLICATION NOTE
Ver. 1.4
8. Design Notes
8. 1 External Components
Please take care to use properly rated, including derating as necessary, and proper type of components.
▪ Input and output electrolytic capacitors. Apply proper derating against ripple current, voltage, and temperature rise.
Use of high ripple current and low impedance types, designed for switch mode power supplies, is recommended.
▪ Transformer. Apply proper derating against core temperature rise from core loss and copper loss.
▪ Current sensing resistor R1 (ROCP). A high frequency switching current flows to R1 (ROCP), and may cause poor
operation if a high inductance resistor is used. Choose a low inductance and surge-proof type.
8. 2 Component Layout and Trace Design
PCB circuit trace design and component layout affect proper
functioning during operation, EMI noise, and power dissipation.
Therefore, where high frequency current traces form a loop, as in
fig.8-1, wide, short patterns and small circuit loops are important.
In addition, local GND and earth ground traces affect radiated
EMI noise, thus the same measures should be taken into account.
Switching mode power supplies consist of current traces of high
Fig.8-1 High frequency current loops
(hatched areas)
frequency and high voltage, thus trace design and component
layouts should be done to comply with all safety guidelines.
Furthermore, in the case where a MOSFET is being used as the
switching device, take into account the positive thermal
coefficient of RDS(on) when preparing a thermal design.
(1) S/GND terminal to R1 (ROCP) to C1 to T1 [winding P] to D/ST terminal Trace Layout
This is the main circuit containing the switching current, and thus it should be as wide and as short as possible.
In case the distance between C1 and the device is lengthy, an isolation capacitor near the device or the
transformer is recommended.
The capacitors may be either electrolytic or film type capacitors, 0.1 µF, in the range considered maximum
input voltage.
(2) S/GND terminal to C2 to T1 [winding D] to R2 to D1 to C2 to VCC terminal Trace Layout
This circuit also needs to be as wide and short as possible. In case the distance between C2 and the device is
not short, placing a 0.1 µF / 50 V film capacitor between VCC and S/OCP terminals is recommended.
(3) R1 (ROCP) Trace Layout
Place R1 (ROCP) as close as possible to S/GND terminal. There should be a single connection (A in fig.8-2)
between the power pattern and the control circuit pattern, and a single connection (B in fig.8-2) between the
power pattern and the OCP terminal pattern close to R1 (ROCP), in order to reduce the common impedance of
the pattern and to avoid interference from the switching current to the control circuit.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.27
STR-L6400 APPLICATION NOTE
Ver. 1.4
D2
C1
P
STR-L6400
C7
S
R2
D1
C2
1～3
D/Startup
Z1
6
D
VCC
8
BD
T1
BD
R3(R )
Cont.FB
7
C10
V
)
(C
10
ADJ
R4
Power
OCP
9
S/GND
5
Control
A
R1
OCP
(R
)
C3 C4 C5 C6 PC1
B
C11
Fig.8-2 External component layout
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.28
STR-L6452 相关器件
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