8. FUNCTIONAL DESCRIPTION
6
EPSON
S1F76980 Technical Manual (Rev.1.0)
8. FUNCTIONAL DESCRIPTION
8.1 Operation Description
The S1F76980 series is a low consumption current power supply input control IC, which monitors the voltage
of 3-system input power supply and is capable of continuously switching power supply of the system selected in
the priority sequence in the IC. The voltage limiter function of output voltage is included in the switching
control circuit to control the output voltage V
OUT
not to exceed the set voltage, using the voltage dividing ratio
of an external resistor. For operations below the operating voltage, the function also guarantees operations in
reduced power mode by setting the output level of the control signal to Hi-Z.
8.2 Power Voltage Monitoring Circuit (V
CC
, V
BUS
, V
BAT
)
This circuit monitors input voltage of each power supply pin and detects low voltage. It inputs the dividing
voltage (V
REG
) of the resistors R1, R2, and R3 connected between power supplies and the reference voltage
(V
REF
) generated in the IC to the comparator for detecting voltage. The comparator detects a potential
difference between V
REG
and V
REF
even if it is inappreciable; therefore, a hysteresis circuit is added to avoid a
possible defective condition due to power noise or the like.
In the example below, the detecting voltage (-V
DET
) with input voltage lowered and the release voltage (+V
DET
)
with input voltage raised are set using the following formulas:
Detecting voltage: -V
DET
= (R2 + R3) / R3)
x
V
REF
(Formula 8.2.1)
Release voltage: +V
DET
= (R1 + R2 + R3 / R3)
x
V
REF
(Formula 8.2.2)
The power line is equipped with an output guarantee circuit that turns the power off when the voltage drops to
below the output guarantee voltage and forces to set the *DET (*=C/U/B) pin to Hi-Z by fixing the XOFF
signal to LOW
Fig.8.2.1 shows the V
CC
power voltage monitoring circuit.
Fig.8.2.2 shows the V
BUS
power voltage monitoring circuit.
Fig.8.2.3 shows the V
BAT
power voltage monitoring circuit.
Fig.8.2.1 Block diagram for V
CC
power voltage monitoring circuit
V
CC
CMP
+
-
CDET
V
REF
R2
R3
The power is turned off when the voltage is below the
output guarantee voltage.
R1
Output
guarantee
V
REG
XOFF
