s-8425 Seiko Instruments Inc., s-8425 Datasheet - Page 9

• Manufacturer Part Number: s-8425
• Description: Battery Backup Switching Ic
• Manufacturer: Seiko Instruments Inc.

The internal configuration of the S-8425 Series is as follows.
The functions and operations of the above-listed elements are described below.
1. Voltage Regulators
2. Voltage Detector
Rev.2.3
Operation
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The S-8425 Series features on-chip voltage regulators with a small dropout voltage. The voltage of the
VRO, VOUT, and VCH pins (the output pins of the voltage regulator) can separately be selected for the
output voltage in 0.1 V steps between the range of 2.3 to 5.4 V.
[Dropout voltage V
Assume that the voltage output from the VRO pin is V
described in the electrical characteristics table. V
voltage from the VRO pin becomes 98% of V
dropout voltage V
Similarly, assume that the voltage of the VOUT pin is V
of output voltage 2 and 3 described in the electrical characteristics table. V
input voltages at which the output voltage from the VOUT pin becomes 98% of V
respectively. Then, the dropout voltages V
The S-8425 Series incorporates two high-precision, low power consuming voltage detectors with hysteresis
characteristics. The power of the CS voltage detector is supplied from the VIN and VBAT pins. Therefore,
the output is stable as long as the primary or backup power supply is within the operating voltage range (1.7
to 16 V). All outputs are Nch open-drain, and need pull-up resistors of about 100 kΩ.
2.1 CS Voltage Detector
The CS voltage detector monitors the input voltage V
selected from between 2.4 and 5.3 V in 0.1 V steps. The result of detection is output at the CS pin: “Low”
for lower voltage than the detection level and “High” for higher voltage than the release level (however,
when the VOUT pin voltage is the CS output inhibit voltage (V
Voltage regulator 1, which stabilizes input voltage V
Voltage regulator 2, which stabilizes input voltage V
Voltage regulator 3, which stabilizes input voltage V
CS voltage detector, which monitors input voltage V
RESET voltage detector, which monitors output voltage V
Switch unit
_00
drop1
V
V
V
drop1
drop1
drop2
drop3
is calculated by the following expression.
Figure 6 Definition of Detection and Release Voltages
, V
Input voltage
Output voltage
= V
= V
= V
drop2
IN1
IN2
IN3
, V
− V
− V
− V
drop3
RO(E)
OUT(E)
CH(E)
]
× 0.98
× 0.98
Seiko Instruments Inc.
× 0.98
drop2
and V
RO(E)
IN1
when the input voltage V
drop3
is defined as the input voltage at which the output
IN
IN
IN
IN
IN
OUT(E)
and outputs it to V
and outputs it to V
and outputs it to V
(VIN pin voltage). The detection voltage can be
are calculated by the following expression.
RO(E)
OUT
SW2
BATTERY BACKUP SWITCHING IC
, and V
Release voltage
Detection voltage
under the conditions of output voltage 1
), a low level is output).
CH(E)
respectively under the conditions
RO
OUT
CH
IN2
IN
and V
is decreased. Then, the
IN3
S-8425 Series
are defined as the
OUT(E)
and V
CH(E)
9
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