AN8014 Panasonic Semiconductor, AN8014 Datasheet - Page 9

• Manufacturer Part Number: AN8014
• Description: Step-down/ step-up/ or inverting DC-DC converter control IC
• Manufacturer: Panasonic Semiconductor

Voltage regulators
[1] Function descriptions (continued)
4. Timer latch short-circuit protection circuit
5. Low input voltage malfunction prevention circuit (U.V.L.O.)
Application Notes (continued)
or deterioration when overload or short-circuit of power supply lasts a certain time.
output level of the error amplifier.
and the short-circuit protection comparator is well balanced.
higher, the short-circuit protection comparator outputs low-level voltage. Then, by cutting off the transistor Q1,
the external capacitor C
following formulas.
the totem-pole output pin will be set to low level and the dead-time will be set to 100%.
reduces to approximately 30 mV. The latch circuit cannot be, however, reset until power supply to the AN8014S
is turned off.
supply voltage is dropped during transient time at power on or off.
accordance with the supply voltage level. When the supply voltage is turned on, it sets the dead-time of Out pin
(pin 13) to 100% and keeps the DTC pin (pin 4) and S.C.P. pin (pin 5) low level until the supply voltage reaches
3.1 V. When the supply voltage falls, it will operate even below 2.96 V because of its hysteresis width of 140 mV.
This circuit protects external main switching devices, flywheel diodes, choke coils and so forth from breakdown
Figure 3 shows the short-circuit protection circuit. The timer latch short-circuit protection circuit detects the
If the output voltage of the DC-DC converter is stable, the output of the error amplifier from the FB pin is stable
In that case, the transistor Q1 is conductive and the S.C.P. pin voltage is approximately 30 mV constantly.
If the load condition changes radically and output signal voltage of the error amplifier (FB) is 1.87 V or
I
If R
When the external capacitor C
When the latch circuit is turned on, the S.C.P. pin will discharge electricity till the voltage on the S.C.P. pin
This circuit protects system from breakdown or deterioration caused by malfunction in control circuit when
The low input voltage malfunction prevention circuit detects internal reference voltage which changes in
IN
IN
CHG
FB
V
0.75 V
C
I
CHG
S
PE
T
is constant current which is determined by the timing resistor R
is 15 k , I
6
7
8
I
CHG
V
V
STBY
R
0.03 V
RT
Error amp.
T
0.72
t
CHG
PE
I
11
CHG
1
S
I
will be approximately 2.3 A.
[F]
CHG
of S.C.P. pin (pin 5) starts charging with the current I
[A]
t
C
PE
S
t
C
1.82 V
PE
S
S.C.P.
comp.
Figure 3. Short-circuit protection circuit
[V]
S
is charged up to approximately 0.75 V, the latch circuit will be turned on. Then
I
CHG
Q1
S.C.P.
5
C
S
Q2
S
R Q
Latch
T
.
Q
CHG
Cut output off
V
REF
which is obtained from the
AN8014S
9