AN8037 Panasonic Semiconductor, AN8037 Datasheet - Page 9

• Manufacturer Part Number: AN8037
• Description: AC-DC switching power supply control IC with standby mode
• Manufacturer: Panasonic Semiconductor

Voltage Regulators
[1] Operation descriptions (continued)
V
Application Notes (continued)
TH(OFF)
V
Out pin voltage
CF pin voltage
L2 CF
Oscillation circuit (continued)
V
V
H CF
CC
Setting the off-period
Refer to figure 3.
time required for the input voltage on the TR pin to drop below the threshold voltage or the minimum off-
period (T
The minimum off-period is the charge period from V
An approximate minimum off-period of the power MOSFET is obtained from the following formula.
When the IC is in local resonance operation, the off-period is determined by the longer one of either the
Thus the power MOSFET is in continuous on/off operation.
2.4 V
0.2 V
1.5 V
T
T
C
V
V
I
I
PC
4 V
0 V
0 V
OFF1
OFF2
OFF(min)
OFF(min)
CF
FB
TH(OFF)
OFF(min)
FB
T
V
I
I
: Minimum off-period
: Value of a capacitor connected to the CF pin
: Voltage internally converted from feedback signal I
: Threshold voltage of V
: Charge current until CF pin voltage increases from 0.2 V to 2.4 V
: Charge current until CF pin voltage increases from 2.4 V to V
OFF1
OFF2
OFF(min)
) specified by the C
TH(OFF)
C
{C
20 k
I
Current mirror
T
CF
FB
CF
OFF
Figure 3. Off-period block diagram and control waveform
660 A typ.
160 A typ.
1 : 5
V
0.6 mA
V
TH(OFF)
2.4 V typ.
TH(OFF)
V
FB
AN8027, AN8037
/I
I
(I
I
(I
OFF
OFF
On
OFF1
/ I
FB
FB
OFF1
CF
0.6 mA)
0.6 mA)
V
.
660 A typ.
160 A typ.
(I
FB
}
FB
FB
to extend off-period
{C
0.6 mA)
CF
V
TH(OFF)
V
(V
Out pin voltage
I
L2 CF
C
CF pin voltage
OFF
FB
V
V
CF
H CF
CC
L-CF
V
Out
GND
V
CC
TH(OFF)
2.4 V
0.2 V
1.5 V
E
0 V
0 V
4V
IN
0.2 V (typical) to V
) / I
FB
OFF2
T
OFF(min)
} (I
T
I
FB
NP
NB
OFF
FB
FB
0.6 mA
AN8027, AN8037
TH(OFF)
0.6 mA)
or V
I
T
FB
OFF(min)
On
; large
FB
.
V
FB
; large
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