an8021l Panasonic Corporation of North America, an8021l Datasheet - Page 15

• Manufacturer Part Number: an8021l
• Description: Ac-dc Switching Power Supply Control Ic
• Manufacturer: Panasonic Corporation of North America

Voltage Regulators
[3] Design reference data (continued)
2. Setting the timer latch period
3. Setting the soft start time
4. Start circuit
Application Notes (continued)
1) When the overload shutting-off condition is kept, the shut-off bias current (OVP operating bias current) of the
2) When automatic reset is desired after the overload shut-off, the standby current of the AN8021L and AN8021SB
to the time when the overvoltage protector is activated, can be set to any desired value by using the external
capacitance C
[Reference calculation formula]
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 AN8021L and AN8021SB 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]
time makes the power supply to rise slowly.
[Setting the start resistor R1]
[Setting the C1]
up to the time when the supply current is supplied from the auxiliary bias coil. Therefore set the C1 as shown in
the following equation:
Soft start charge current
The timer latch period t, the period from the time when an abnormality of the power supply output is detected
Most of the conventional ICs are charged by using the internal resistor from the internal reference voltage, or
The start time from the power-on to the actual start can be set by using the values of R1 and C1. Too long start
AN8021L and AN8021SB is 550 A (typical) at V
equation :
is 70 A (typical) at V
When the AN8021L or AN8021SB is started, the operating supply current of 7.5 mA is required at V
The current should be supplied with the discharge current of the C1 during the period from the soft start time
TIM/OVP capacitor terminal for timer latch period setting
t
SS (C5)
t
C
C
2
5
(V
I
· V
I
TIM
· V
V
R
SS
TIM
CC(START)
1
IN
550 A
TIM
capacitor terminal for soft start
SS
(C2) based on the following equation:
V
10 V
[s]
[s]
IN
550 A
7.5 mA
10 V
V
CC
R
CC(STOP)
V
I
(Varies depending on R7 value, at R7
I
(Varies depending on R7 value, at R
I
V
V
1
TIM
SS
SS
TIM
SS
SS
12 V. Therefore, set the R1 as shown in the following equation :
= 2.0 V, at duty = 0%
= 4.1 V, at maximum duty
V
I
soft start charging current
30 A (typ.)
TIM
IN
timer latch charge current
) · C
70 A
6 V (typ.): Overvoltage protection threshold value
12 V
1
30 A (typ.)
Soft start time
CC
10 V. Therefore, set the R1 as shown in the following
T
(R7)
19 k )
19 k )
AN8021L, AN8021SB
CC
18 V.
15