S-35392A Datasheet, PDF (19/47 Pages) Seiko Instruments Inc – 2-WIRE REAL-TIME CLOCK

Rev.1.3_00
2-WIRE REAL-TIME CLOCK
S-35392A
„ Low Power Supply Voltage Detection Circuit
The S-35392A has a low power supply voltage detection circuit, so that users can monitor drops in the power supply
voltage by reading the BLD flag (B1 in the status register 1). There is a hysteresis width of approx. 0.15 V (Typ.) between
detection voltage and release voltage (refer to “„ Characteristics (Typical Data)”). The low power supply voltage
detection circuit does the sampling operation only once in one sec for 15.6 ms.
If the power supply voltage decreases to the level of detection voltage (V_DET) or less, “1” is set to the BLD flag so that
sampling operation stops. Once “1” is detected in the BLD flag, no sampling operation is performed even if the power
supply voltage increases to the level of release voltage or more, and “1” is held in the BLD flag. After initialization, or once
the BLD flag is read, the BLD flag is automatically set to “0” to restart the sampling operation.
If the BLD flag is “1” even after the power supply voltage is recovered, be sure to initialize the circuit. Without initializing,
Read in the next BLD flag is done after sampling, the BLD flag gets reset to “0”. In this case, be sure to initialize although
the BLD flag is in “0” because the internal circuit may be in the indefinite status.
V_DD
Detection voltage
Hysteresis width
0.15 V approximately
Release voltage
BLD flag
reading
1s
1s
15.6 ms
Sampling pulse
Stop
Stop
Stop
BLD flag
Figure 20 Timing of Low Power Supply Voltage Detection Circuit
„ Circuits Power-on and Low Power Supply Voltage Detection
Figure 21 shows the changes of the POC flag and BLD flag due to V_DD fluctuation.
Low power supply
V_DD
voltage detection
voltage
POC flag
BLD flag
Status register 1
reading
Figure 21 POC Flag and BLD Flag
Seiko Instruments Inc.
Low power supply
voltage detection
voltage
V_SS
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