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參數(shù)資料
| 型號： | AN8038S |
| 廠商： | PANASONIC CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | AC-DC switching power supply control IC with RCC local resonance circuit for improved conformance with energy conservation laws |
| 中文描述： | 2 A SWITCHING CONTROLLER, PDSO8 |
| 封裝： | 0.225 INCH, PLASTIC, SOP-8 |
| 文件頁數(shù)： | 13/22頁 |
| 文件大小： | 179K |
| 代理商： | AN8038S |
Voltage Regulators
AN8038, AN8038S
13
I
Application Notes (continued)
[2] Operation descriptions (continued)
2. Oscillator circuit (continued)
Notes on setting the oscillator frequency
This section describes the calculation of the on- and off-periods.
1) On-period: t
ON
The output on-period is the discharge period when the CF pin is between the peak value of V
CFH
=
4.2
V (typical) and V
FB
.
The following formula can be used to calculate the on-period of the power MOSFET as a reasonable
approximation. (See figure 2.)
t
ON
=
C
CF
×
(V
CFH
V
FB
) / I
ON
Here,
V
CFH
=
4.2 V typ.
I
ON
=
I
TR
+
280
μ
A typ.
I
TR
=
(E
IN
×
NB/NP) / (R
TR1
+
R
TR2
)
V
FB
=
0.7 V typ.
(When I
IFB
≤
250
μ
A)
V
FB
=
4 k
×
(I
IFB
250
μ
A)
+
0.7 V
(When I
IFB
>
250
μ
A)
2) Off-period: t
OFF
The minimum off-period is the charging period from V
CFL
=
0.2 V (typical) to V
RSTB
.
The following formula can be used to calculate the minimum off-period as a reasonable approximation.
(See figure 3.)
t
OFF(min)
=
C
CF
×
{V
RSTB
V
CFL
} / I
OFF
I
OFF1
=
1250
μ
A typ. (V
FB
0.7 V typ. to V
RSTB
)
I
OFF2
=
55
μ
A typ.
(V
FB
V
RSTB
to 4.2 V typ.)
t
ON
t
OFF(min)
C
CF
V
CFH
V
CFL
V
RSTB
:On-period
:Minimum off-period
:Capacitance of the capacitor connected to the CF pin
:Upper limit voltage for the CF pin.
:Lower limit voltage for the CF pin
:Pin voltage that sets the light load detection level.
This voltage can be adjusted with an external resistor.
:Value that results from IC internal conversion of feedback current I
IFB
:On-period (CF pin discharge) current
:Off-period (CF pin charge) current when I
IFB
<
1 mA
:Off-period (CF pin charge) current when I
IFB
>
1 mA
:Flowing current at TR pin
:Primary winding voltage
:Number of turns in the bias winding
:Number of turns in the primary winding
R
TR1
/R
TR2
:Resistors connected to the TR pin
V
CFH
=
4.2 V typ.
V
RSTB
=
3.5 V typ.
V
FB
I
ON
I
OFF1
I
OFF2
I
TR
E
IN
N
B
N
P
However, the off-period for the local resonance circuit described later, is determined by the time for
the voltage fed back to TR pin (pin 1) if that time is longer than the t
OFF
time determined by C
CF
.
The power MOSFET is turned on and off continuously by repeating the above operations.
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