an8027 Panasonic Corporation of North America, an8027 Datasheet - Page 26

• Manufacturer Part Number: an8027
• Description: Ac-dc Switching Power Supply Control Ic With Standby Mode
• Manufacturer: Panasonic Corporation of North America

AN8027, AN8037
26
[1] Operation descriptions (continued)
16. Overcurrent protection circuit (input voltage correction function) (continued)
17. Overcurrent protection circuit (Timer latch protection)
Application Notes (continued)
nected to the Out pin from damage in most cases if the primary winding is short-circuited and excessive current
flows to the power MOSFET.
primary winding, this circuit charges the capacitor connected to the SD pin, shut down the power supply, and
holds this state. (Refer to figure 29.)
[Setting the timer period]
The timer period (T
T
CLM
Example: If T
The CLM pin is used for timer latch in addition to pulse-by-pulse overcurrent protection.
This is because the pulse-by-pulse overcurrent protection alone cannot prevent the power MOSFET con-
If an excessive current flows to the power MOSFET for a certain period due to the short-circuiting of the
Power MOSFET
SD
{C
I
(I
CLM(AVE)
pin voltage
T
CLM
SD
IM
current
V
I
(V
OFF
500 ms
DS
SD
100 A)
0
0
TH1-SD
V
V
/ T is 50%, C
V
CLM
I
I
DS
CLM
CLM
DS
B
0 V
0 V
0 A
0 V
) is obtained from the following formula.
V
T
STB-SD
OFF
SD
/T
V
)}/I
Winding short-circuiting
is 10 F.
STB SD
CLM(AVE)
Input voltage; larger
Amount of correction;
larger
Figure 28
1.5 V
Figure 29
C
V
V
I
T
T
CLM
OFF
SD
TH1-SD
STB-SD
: Capacitor connected to SD pin
: Shutdown operating threshold voltage
: Shutdown standby voltage
: CLM timer charge current (100 A)
: Off-period
: Cycle
Correction corresponding
to the input voltage
Input voltage
FB voltage
V
FF voltage
TH1 SD
E
IN
3.9 V typ.
Voltage Regulators
Power supply
Power supply
stop
stop
Time
Time