S-8426AAA-J8T1X Datasheet, PDF (9/37 Pages) Seiko Instruments Inc – BATTERY BACKUP SWITCHING IC

Rev.2.0_02
BATTERY BACKUP SWITCHING IC
S-8426A Series
 Operation
The internal configuration of the S-8426A Series is as follows.
• Voltage regulator 1, which stabilizes input voltage (VIN⁾ and outputs it to VRO
• Voltage regulator 2, which stabilizes input voltage (VIN⁾ and outputs it to VOUT
• CS voltage detector, which monitors input voltage (VIN⁾
• PREEND voltage detector, which monitors output voltage (VBAT⁾
• RESET voltage detector, which monitors output voltage (VOUT⁾
• Switch unit
The functions and operations of the above-listed elements are described below.
1. Voltage Regulators
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 Vdrop1, Vdrop2
Assume that the voltage output from the VRO pin is VRO(E) under the conditions of output voltage 1 described
in the electrical characteristics table. VIN1 is defined as the input voltage at which output voltage from the VRO
pin becomes 98% of VRO(E) when the input voltage VIN is decreased. Then, the dropout voltage Vdrop1 is
calculated by the following expression.
Vdrop1 = VIN1 − VRO(E) × 0.98
Similarly, assume that the voltage of the VOUT pin is VOUT(E) under the conditions of output voltage 2 described
in the electrical characteristics table. VIN2 is defined as the input voltage at which the output voltage from the
VOUT pin becomes 98% of VOUT(E). Then, the dropout voltage Vdrop2 is calculated by the following expression.
Vdrop2 = VIN2 − VOUT(E) × 0.98
2. Voltage Detector
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
The CS voltage detector monitors the input voltage (VIN) (VIN pin voltage). The detection voltage can be
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 (VSW2), a low level is output) .
Input voltage
Release voltage
Detection voltage
Output voltage
Figure 13 Definition of Detection and Release Voltages
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