s-8424a Seiko Instruments Inc., s-8424a Datasheet - Page 18

• Manufacturer Part Number: s-8424a
• Description: Battery Backup Switching Ic
• Manufacturer: Seiko Instruments Inc.

18
BATTERY BACKUP SWITCHING IC
S-8424A Series
Operation
The internal configuration of the S-8424A 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-8424A 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.
[Dropout voltage V
The S-8424A 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 k Ω .
2.1 CS Voltage Detector
Assume that the voltage output from the VRO pin is V
described in the electrical characteristics table. V
from the VRO pin becomes 98% of V
voltage V
Similarly, assume that the voltage of the VOUT pin is V
described in the electrical characteristics table. V
voltage from the VOUT pin becomes 98% of V
following expression.
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
drop1
= V
= V
IN1
IN2
is calculated by the following expression.
drop1
− V
− V
Figure 7 Definition of Detection and Release Voltages
RO(E)
OUT(E)
, V
Input voltage
Output voltage
drop2
× 0.98
× 0.98
]
Seiko Instruments Inc.
RO(E)
when the input voltage V
IN
IN
IN
OUT(E)
) and outputs it to V
) and outputs it to V
)
IN1
IN2
OUT
. Then, the dropout voltage V
is defined as the input voltage at which output voltage
BAT
is defined as the input voltage at which the output
IN
)
)
(VIN pin voltage). The detection voltage can be
RO(E)
OUT(E)
Release voltage
Detection voltage
SW2
under the conditions of output voltage 1
under the conditions of output voltage 2
), a low level is output).
RO
OUT
IN
is decreased. Then, the dropout
drop2
is calculated by the
Rev.2.2
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