X1286V14T1 Datasheet, PDF (22/25 Pages) Intersil Corporation – Intersil Real Time Clock/Calendar/CPU Supervisor with EEPROM

X1286
devices have an IRQ- output which can be checked by
setting an alarm for each minute. Using the pulse
interrupt mode setting, the once-per-minute interrupt
functions as an indication of proper oscillation.
Backup Battery Operation
Many types of batteries can be used with the Intersil
RTC products. 3.0V or 3.6V Lithium batteries are
appropriate, and sizes are available that can power a
Intersil RTC device for up to 10 years. Another option
is to use a supercapacitor for applications where Vcc
may disappear intermittently for short periods of time.
Depending on the value of supercapacitor used,
backup time can last from a few days to two weeks
(with >1F). A simple silicon or Schottky barrier diode
can be used in series with Vcc to charge the superca-
pacitor, which is connected to the Vback pin. Do not
use the diode to charge a battery (especially lithium
batteries!).
Figure 16. Supercapactor charging circuit
2.7-5.5V
V_CC
V_back
V_SS
Supercapacitor
Since the battery switchover occurs at Vcc=Vback-
0.1V (see Figure 16), the battery voltage must always
be lower than the Vcc voltage during normal operation
or the battery will be drained.
The summary of conditions for backup battery opera-
tion is given in Table 9:
Table 9. Battery Backup Operation
1. Example Application, Vcc = 5V, Vback = 3.0V
Condition
Vcc
a. Normal Operation
5.00
b. Vcc on with no battery
5.00
c. Backup Mode
0-1.8
Vback
3.00
0
1.8-3.0
Vtrip
4.38
4.38
4.38
Iback
<<1µA
0
<2µA
Notes
Timekeeping only
2. Example Application, Vcc = 3.3V,Vback = 3.0V
Condition
Vcc
Vback
a. Normal Operation
3.30
3.00
b. Vcc on with no battery
3.30
0
c. Backup Mode
0-1.8
1.8-3.0*
d. UNWANTED - Vcc ON, Vback
powering
2.65 - 3.30
> Vcc
*since Vback>2.65V is higher than Vtrip, the battery is powering the entire device
Vtrip
2.65
2.65
2.65
2.65
Iback
<<1µA
0
<2µA*
up to 3mA
Timekeeping only
Internal Vcc=Vback
22
FN8101.1
April 14, 2006