S8424A datasheet(20/46 Pages) SII

20 / 46 page

BATTERY BACKUP SWITCHING IC

S-8424A Series

Rev.3.0_01

2.2 PREEND Voltage Detector

The PREEND voltage detector monitors the input voltage VBAT (VBAT pin voltage). The detection voltage

can be selected from between 1.7 V and 3.4 V in 0.1 V steps. A higher voltage can also be seclected

keeping a constant difference with the RESET voltage. This function enables the warning that the backup

battery is running out. The detection result is output to the PREEND pin: “Low” for lower voltages than

the detection voltage and “High” for higher voltages than the release voltage. The power supply of the

PREEND

voltage detector is supplied from the VIN pin. The output is valid only when the voltage is

supplied from the VIN pin to the VOUT pin (VIN

≥ VSW1). The output is the low level when the voltage is

supplied from the VBAT pin to the VOUT pin (VIN < VSW1).

2.3 RESET Voltage Detector

The RESET voltage detector monitors the output voltage VOUT (VOUT pin voltage). The detection

voltage can be selected from between 1.7 V and 3.4 V in 0.1 V steps. The result of detection is output at

the RESET pin: “Low” for lower voltages than the detection level and “High” for higher voltages than

the release level. RESET outputs the normal logic if the VOUT pin voltage is 1.0 V or more.

Caution The PREEND and RESET voltage detectors use the different pins, respectively.

Practically, the current is taken from the VBAT side, and consider the I/O voltage

difference (Vdif) of M1 when M1 is ON.

3. Switch Unit

The switch unit consists of the VSW1 and VSW2 detectors, a switch controller, voltage regulator 2, and switch

transistor M1 (Refer to “Figure 8 Switch Unit”).

REG2

VOUT

VBAT

VIN

Switch

controller

VSW1

detector

VSW2

detector

Figure 8 Switch Unit

3.1 VSW1 Detector

The VSW1 detector monitors the power supply voltage VIN and sends the results of detection to the switch

controller. The detection voltage (VSW1) can be set to 77

±2% or 85 ±2% of the CS release voltage

+VDET1.

S8424A Datasheet(PDF) 20 Page - Seiko Instruments Inc