HIGH WITHSTAND-VOLTAGE VOLTAGE REGULATOR WITH RESET FUNCTION
S-87x Series
Rev.8.0_00
Seiko Instruments Inc.
30
5. Voltage detection circuit
The built-in voltage detection circuit (Nch opendrain type) is equivalent to our S-808 Series/S-809 Series
voltage detectors. A pull-up resistor of about 100 kΩ is required for output. Since the comparator power
of this circuit is supplied from VIN pin, this circuit operates while voltage is applied to VIN pin.
The detection voltage of the voltage detector can be selected as follows:
2.1 V to 11.3 V±2.4 % (0.1 V step)
In the F type, the release voltage (+V
DET
) accuracy is ±1.1 %. So, it responds to the application for
overcharge detection of lithium-ion battery packs.
In the E type, the input voltage monitoring pin of the voltage detector is externally connected as the
SENSE pin. Because this pin is configured by a resistor only, temporary current such as a through-type
current does not flow. Consequently even when resistor (R
IN
) is inserted between input power supply and
VIN pin, the input power voltage can be accurately monitored by connecting the SENSE pin to the input
power supply. Also, when a drop in the SENSE pin input voltage is detected, the voltage detector
generates a reset signal. At the same time, it powers off the voltage regulator.
Caution 1. As shown in Figure 23 to 25, when connecting V
OR
output to
PF pin in the C type or
connecting SENSE pin to VIN pin in the E type, the following phenomena occur if
resistor (R
IN
) is connected between input voltage and VIN pin. Be careful.
(1) At the time of voltage detection, the voltage regulator is shutdown and load
current is cut. Therefore, VIN pin voltage increases by ΔV
IN
=I
IN
×R
IN
, where the
current flowing into R
IN
is set to I
IN
. Hence, if ΔV
IN
exceeds hysterisis width
(V
HYS
), oscillation starts immediately after detection and continues. It is
necessary to set ΔV
IN
less than V
HYS
.
(2) At the time of voltage release, the voltage regulator is powered on and load
current flows. Therefore, if ΔV
IN
exceeds hysterisis width (V
HYS
), oscillation
starts immediately after release and continues. It is necessary to set ΔV
IN
less
than V
HYS
. Also at the time of voltage release, the rush current to charge output
capacitor (C
OUT
) flows. Hence, oscillation momentarily starts until the output of
regulator (V
OUT
) rises high enough even though ΔV
IN
is set less than V
HYS
. But
Short-circuit protection circuit controls the rush current less than I
MAX
on
Figure 19 to 21. If this momentary oscillation is a problem in your applicaion,
setting R
IN
less than V
HYS
/I
MAX
prevents oscillation.
VSS
VOR
VIN
VPF
VOUT
I
IN
R
IN
R
L
C
OUT
S-87xxxxCUP
Figure 23 Attention connecting example 1
