RV5C339A_03 Datasheet, PDF (33/46 Pages) RICOH electronics devices division – 3-WIRE SERIAL INTERFACE REAL-TIME CLOCK IC WITH VOLTAGE MONITORING FUNCTION

RV5C339A
Considerations in Using Oscillation Halt Sensing Circuit
Be sure to prevent the oscillation halt sensing circuit from malfunctioning by preventing the following:
1) Instantaneous power-down on the VDD
2) Condensation on the crystal oscillator
3) On-board noise to the crystal oscillator
4) Applying to individual pins voltage exceeding their respective maximum ratings
In particular, note that the XSTP bit may fail to be set to 1 in the presence of any applied supply voltage as
illustrated below in such events as backup battery installation. Further, give special considerations to prevent
excessive chattering to power supply.
VDD
< Supply Voltage Sensing Circuit >
The supply voltage monitoring circuit is configured to conduct a sampling operation during an interval of 7.8ms per
second to check for a drop in supply voltage below a threshold voltage of 2.1 or 1.6 volts for the VDSL bit setting of 0
(the default setting) or 1, respectively, in the control register 2, thus minimizing supply current requirements as
illustrated in the timing chart below. This circuit suspends a sampling operation once the VDET bit is set to 1 in the
control register 2.
VDD
XSTP
Internal initialization period
(1 or 2 seconds)
Sampling operation by supply voltage
monitoring circuit
VDET
(D6 at address Fh)
7.8ms
1s
Setting 0 to XSTP
and VDET bits
Threshold voltage
of 2.1 or 1.6 volts
Setting VDET bit to 0
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