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S1F76300 Series
4–14 EPSON S1F70000 Series
Technical Manual
Reference voltage generator and output
voltage regulator
The reference voltage generator regulates VI1 to gener-
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
O and GND. These
series use an on-chip resistor to set the output at a speci-
fied voltage.
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
DET, is fixed internally at 1.05 ± 0.05V.
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
I1 drops below VDET, Tr1 and Tr2 conduct and
PWCR and RST are grounded. If V
I1 recovers and rises
higher than V
REL, Tr1 turns OFF. The detection volt-
age hysteresis is 5% (Typ.) and V
REL is VDET × 1.05
(Typ.).
V
O returns to its normal value when the voltage of
PWCR increases and Tr2 turns OFF, so that RST re-
turns to V
O after a delay specified by the time coeffi-
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
I1 exceeds VDET, the drain is opened and, when
V
I1 drops below VDET again, the output transistor con-
ducts and the output is grounded. The characteristic re-
sponse is shown in the following figure.
Disabling power-on clear
Always connect PWCR to either VO or GND. If volt-
age detection only is required, remove the resistor be-
tween PWCR and V
O and monitor the level at RST. If
neither function is required, connect PWCR to GND.
Leaving PWCR unconnected results in an undefined in-
verter gate voltage in the V
O circuit, causing transient
currents to flow between V
O and GND.
Reference
voltage
generator
CR
oscillator
+
–
A
V
I1
V
SW
V
O
GND
Output
voltage regulator
Voltage
detector
V
I1
+
–
Tr1
Tr2
V
O
V
O
V
O
RST
PWCR
R2
R1
C1
S1F76310M
V
REL
V
I1
PWCR
RST
V
DET
V
GND
V
GND
V
O
V
O