an8022l Panasonic Corporation of North America, an8022l Datasheet - Page 14

• Manufacturer Part Number: an8022l
• Description: Ac-dc Switching Power Supply Control Ic
• Manufacturer: Panasonic Corporation of North America

AN8022L, AN8022SB
14
[3] Design reference data
1. Setting the output frequency
2. Setting the timer latch period
3. Setting the soft start time
Application Notes (continued)
Output frequency
However, it may deviate a little from the design value due to delay of the internal circuit.
(Reference value)
to the time when the overvoltage protector is activated, can be set to any desired value by using the external
capacitance C
[Reference calculated value]
by using the constant current source which is determined by the internal resistance. However, the above charging
method suffers from problems on dispersion or temperature change and can not ensure the soft start time. For this
reason, the AN8022L and AN8022SB use the following method: The soft start charge current is given from the
constant current source used in the internal triangular wave oscillation circuit. In addition, the above constant
current source is stable with respect to dispersion or fluctuation with temperature because it has the current value
which is determined by the external resistor and the terminal voltage given from the resistor-divider of internal
reference voltage. However, for this method, particular care should be taken on the application: Since each time
the setting of oscillation frequency is changed, the soft start constant should be also changed.
[Reference calculation formula]
Soft start charge current
V
V
CT (C6) Capacitor terminal for triangular oscillation
RT (C7) Resistor terminal for triangular oscillation
OSC
OSC
The output is controlling the triangular oscillation with PWM control: Triangular oscillation frequency
f
at C
The timer latch period t, the period from the time when an abnormality of the power supply output is detected
t
Most of the conventional ICs are charged by using the internal resistor from the internal reference voltage, or
t
OUT
TIM/OVP Capacitor terminal for timer latch period setting
SS (C5)
T
C
C
(C6)
5
H
L
2
approximately 200 kHz
I
I
· V
· V
SS
TIM
TIM
SS
TIM
Capacitor terminal for soft start
220 pF and R
(C2) based on the following equation:
T
[s]
1
[s]
T
2
T
(R7)
V
I
(Varies depending on R7 value, at R7 19 k )
I
(Varies depending on R7 value, at R7
I
V
V
TIM
SS
SS
TIM
SS
SS
Soft start charging current
30 A (typ.)
2.0 V, at duty
4.1 V, at maximum duty
19 k
Timer latch charge current
V
6 V (typ.): Over voltage protection threshold value
I
TIM
30 A (typ.)
[Reference calculation formula]
V becomes approximately 3 V, the output frequency is obtained
in the following equation:
T
Since the I
f
OUT
1
0%
T
2
T
1
RT
1
2I
T
RT
is given by rough calculation of 2.5 V/R
2
(charge/discharge current)
C
19 k )
I
6
RT
· V
C
6
· V
Voltage Regulators
6 · C
5
6
· R
7
T
and