an8041s Panasonic Corporation of North America, an8041s Datasheet - Page 11

• Manufacturer Part Number: an8041s
• Description: Liquid Crystal Backlight Control Ic
• Manufacturer: Panasonic Corporation of North America

Voltage Regulators
[3] Function descriptions (continued)
4. Timer latch short-circuit protection circuit
5. Low input voltage malfunction prevention circuit (U.V.L.O.)
Application Note (continued)
prevents the parts such as external main switch device, flywheel diode, the choke coil from destruction or deterioration.
the output level of the error amplifier 1 and 2 blocks. When either the DC-DC converter output voltage or the lamp
current detection voltage is stable, the output of that error amplifier is stabilized and the short-circuit protection
comparator also maintains balance.
block (FB1, FB2) become 1.82 V or higher, the short-circuit protection comparator outputs low-level and cut off
the transistor Q1, thereby the external capacitor C
given by the following equation:
2.3 A when R
output terminal to low-level and sets the dead-time to 100%.
the latch circuit is set, it is not reset unless the power supply is turned off.
circuit protects the system from destruction or deterioration due to the malfunction of the control circuit.
the period from the time when the supply voltage starts to rise and to the time when it reaches 3.1 V, it keeps the dead-
time of the Out terminal (pin 13) to 100% and maintains the DTC terminal (pin 4) and the S.C.P. terminal (pin 5) at
low-level. When the supply voltage falls, it holds the hysteresis width of 140 mV and operates at a voltage under
2.96 V.
When the short-circuit or overload of the power supply output continues for a certain period, this circuit
The short-circuit protection circuit is shown in figure 4. The timer latch short-circuit protection circuit detects
When the load conditions are suddenly changed, and both of the outputs of the error amplifier 1 block and 2
I
When the external capacitor C
When the latch circuit is set, the S.C.P. terminal voltage is discharged to approximately 30 mV. However, once
When the supply voltage is dropped under the transient condition such as power-on or operation stop, this
This circuit detects the internal reference voltage which varies according to the supply voltage level. During
CHG
V
0.75 V
C
I
CHG
S
PE
IN 1
IN 1
IN 2
IN 2
is constant current which is determined by the timing resistor R
FB1
FB2
I
CHG
V
STBY
V
R
0.03 V
T
6
7
8
11
10
9
T
RT
Error amp. 1
0.72
15 k .
Error amp. 2
11
t
PE
I
1
CHG
I
[F]
[A]
CHG
t
C
PE
S
t
C
Figure 4. Short-circuit protection circuit
PE
S
S
[V]
is charged to approximately 0.75 V, the latch circuit is set to fix the totem pole
S.C.P. comp.
1.82 V
S
of the S.C.P. terminal (pin 5) starts charging with current I
I
S.C.P.
CHG
Q1
C
Q2
S
T
of the oscillator. It becomes approximately
R
Latch
S Q
Q
Output cut-off
V
REF
AN8041S
CHG
11