3-WIRE REAL-TIME CLOCK
S-35190A
Rev.2.4_00
Low Power Supply Voltage Detection Circuit
The S-35190A 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 (VDET) 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, the internal circuit may be in the indefinite status. In
this case, be sure to initialize the circuit.
VDD
Hysteresis width
0.15 V approximately
Release
voltage
Detection
voltage
BLD flag reading
1 s
1 s
Stop
Stop
Stop
15.6 ms
Sampling pulse
BLD flag
Figure 24 Timing of Low Power Supply Voltage Detection Circuit
Circuits Power-on and Low Power Supply Voltage Detection
Figure 25 shows the changes of the POC flag and BLD flag due to VDD fluctuation.
Low power supply
voltage detection
voltage
Low power supply
voltage detection
voltage
VDD
VSS
POC flag
BLD flag
Status register 1
reading
Figure 25 POC Flag and BLD Flag
20
Seiko Instruments Inc.
SII [ SEIKO INSTRUMENTS INC ]
