s-8426a Seiko Instruments Inc., s-8426a Datasheet - Page 9

• Manufacturer Part Number: s-8426a
• Description: Battery Backup Switching Ic
• Manufacturer: Seiko Instruments Inc.

Rev.1.0
Operation
The internal configuration of the S-8426A Series is as follows.
• Voltage regulator 1, which stabilizes input voltage (V
• Voltage regulator 2, which stabilizes input voltage (V
• CS voltage detector, which monitors input voltage (V
• PREEND voltage detector, which monitors output voltage (V
• RESET voltage detector, which monitors output voltage (V
• Switch unit
The functions and operations of the above-listed elements are described below.
1. Voltage Regulators
2. Voltage Detector
The S-8426A Series features on-chip voltage regulators with a small dropout voltage. The voltage of the VRO and
VOUT 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.
1. 1 Dropout voltage V
The S-8426A Series incorporates three 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 supplies are 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
_00
Assume that the voltage output from the VRO pin is V
in the electrical characteristics table. V
pin becomes 98% of V
calculated by the following expression.
Similarly, assume that the voltage of the VOUT pin is V
in the electrical characteristics table. V
VOUT pin becomes 98% of V
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
V
V
drop1
drop2
= V
= V
IN1
IN2
− V
− V
Input voltage
Output voltage
Figure 13 Definition of Detection and Release Voltages
drop1
RO(E)
OUT(E)
, V
RO(E)
× 0.98
× 0.98
drop2
OUT(E)
when the input voltage V
. Then, the dropout voltage V
Seiko Instruments Inc.
IN1
IN2
is defined as the input voltage at which output voltage from the VRO
is defined as the input voltage at which the output voltage from the
IN
IN
IN
) and outputs it to V
) and outputs it to V
)
OUT
SW2
BAT
)
RO(E)
OUT(E)
), a low level is output) .
)
IN
IN
) (VIN pin voltage). The detection voltage can be
is decreased. Then, the dropout voltage V
BATTERY BACKUP SWITCHING IC
under the conditions of output voltage 1 described
Release voltage
Detection voltage
under the conditions of output voltage 2 described
drop2
RO
OUT
is calculated by the following expression.
S-8426A Series
drop1
is
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