Epson Power Supply IC S1F70000 Technical Manual page 159

S1F76300 Series
Reference voltage generator and output
voltage regulator
The reference voltage generator regulates V
ate a votlage for the voltage regulator and voltage detec-
tion circuits.
The voltage regulator regulates the boosted output
votlage. This is determined by the level at point A be-
tween the two resistors connecting V
series use an on-chip resistor to set the output at a speci-
fied voltage.
Reference
voltage
generator
oscillator
+
–
Note
In step-up voltage operation, the ripple voltage created
by the switching operation is large relative to the output
voltage described above. This ripple voltage is affected
by external components and load conditions. The user
is advised to check this voltage carefully.
Voltage detection
The S1F76310, S1F76380 series are equipped with a
built-in voltage detection function. The detection volt-
age, V , is fixed internally at 1.05
DET
Power-on clear function
The S1F76310 series and S1F76380 series are equipped
with a built-in power-on clear function. As shown in
the following figure, R1 and C1 are connected to
PWCR, and R2 is connected to RST to operate the func-
tion. If V drops below V
I1
PWCR and RST are grounded. If V
higher than V , Tr1 turns OFF. The detection volt-
REL
age hysteresis is 5% (Typ.) and V
(Typ.).
4–14
to gener-
I1
and GND. These
O
Output
voltage regulator
V
I1
V
SW
CR
V
O
A
GND
0.05V.
, Tr1 and Tr2 conduct and
DET
recovers and rises
I1
is V
REL DET
S1F76310M
Voltage
detector
V
I1
V returns to its normal value when the voltage of
O
PWCR increases and Tr2 turns OFF, so that RST re-
turns to V after a delay specified by the time coeffi-
O
cient of R1 and C1. Thus, after normal output has been
obtained, a reset pulse of adjustable width can be ob-
tained which can reset a system connected to RST.
The output from RST is an N-channel, open-drain.
When V exceeds V
I1
V drops below V
I1
ducts and the output is grounded. The characteristic re-
sponse is shown in the following figure.
V
REL
V
I1
V
DET
V
O
PWCR
V
GND
V
O
RST
V
GND
Disabling power-on clear
Always connect PWCR to either V
age detection only is required, remove the resistor be-
tween PWCR and V
neither function is required, connect PWCR to GND.
Leaving PWCR unconnected results in an undefined in-
verter gate voltage in the V
currents to flow between V
1.05
EPSON
Tr2
V
–
Tr1
+
, the drain is opened and, when
DET
again, the output transistor con-
DET
or GND. If volt-
O
and monitor the level at RST. If
O
circuit, causing transient
O
and GND.
O
V
O
R2
RST
V
O
O
R1
PWCR
C1
S1F70000 Series
Technical Manual