S1F71200 Series
Overcurrent Protection Circuit
The overcurrent protection circuit functions when an
overcurrent flows through the current detection resistor
during the step-up operation and the voltage at the
I
pin rises over the set voltage value. When the
SENSE
overcurrent protection function works, the transistor
drive pin SWO comes to the V
ing transistor is turned off. Since the overcurrent pro-
tection circuit links to the soft start circuit, it drops the
voltage at the SSCAP pin to the V
overcurrent detection. When the overcurrent detection
is released, the voltage at the SSCAP pin rises slowly
and the soft start operation starts.
Power lost at the current detection resistor becomes a
factor of lower efficiency. When the overcurrent pro-
tection circuit is not necessary, short-circuit the I
pin to the V
pin. The I
SS
open state.
Operation of Series Regulator
S1F71200 has a built-in series regulator control circuit.
When driving the PNP transistor as an external part,
S1F71200 reduces voltage supplied to the V
constitutes a series regulator. The V
connected to the V
pin of step-up output.
SW
This series regulator operates monitoring voltage at the
V
pin of step-up/step-down output. It controls the
O
drive current (base current of the PNP transistor) at the
EXO pin to stabilize voltage at the V
4–46
level and the switch-
SS
level during
SS
pin cannot be used in an
SENSE
DD2
pin is generally
DD2
pin.
O
Power Off Function
S1F71200 can control circuit operations according to
external signal control. When the POFFX pin is set to
the V
level, all circuits stop and their powers are
SS
turned off. The current consumption at the power off
state is less than 1 A. When the power is off, the SWO
pin is set to the V
V
level and respective external transistors are
DD2
turned.
The voltage at the SSCAP pin comes to the V
and the soft start circuit controls the step-up operation
output voltage is controlled with the soft start circuit af-
ter the power off state is released. The soft start circuit
controls step-up operations after power off release.
When being set to the V
ates in general. The POFFX pin cannot be used in an
SENSE
open state. When the power off function is not used,
connect the POFFX pin to the V
pin and
EPSON
level, the EXO pin is set to the
DD
level, the POFFX pin oper-
DD
pin.
DD1
S1F70000 Series
Technical Manual
level,
SS