x1286v14zt1 Intersil Corporation, x1286v14zt1 Datasheet - Page 22

• Manufacturer Part Number: x1286v14zt1
• Description: Real Time Clock/calendar/cpu Supervisor With Eeprom
• Manufacturer: Intersil Corporation

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!).
Table 9. Battery Backup Operation
*since Vback>2.65V is higher than Vtrip, the battery is powering the entire device
1. Example Application, Vcc = 5V, Vback = 3.0V
a. Normal Operation
b. Vcc on with no battery
c. Backup Mode
2. Example Application, Vcc = 3.3V,Vback = 3.0V
a. Normal Operation
b. Vcc on with no battery
c. Backup Mode
d. UNWANTED - Vcc ON, Vback
powering
Condition
Condition
22
2.65 - 3.30
0-1.8
0-1.8
5.00
5.00
3.30
3.30
Vcc
Vcc
X1286
1.8-3.0*
Vback
1.8-3.0
Vback
> Vcc
3.00
3.00
0
0
Figure 16. Supercapactor charging circuit
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:
2.7-5.5V
Vtrip
Vtrip
4.38
4.38
4.38
2.65
2.65
2.65
2.65
V
CC
up to 3mA
V
SS
<<1µA
<<1µA
<2µA*
Iback
Iback
<2µA
V
0
0
back
Internal Vcc=Vback
Timekeeping only
Timekeeping only
Supercapacitor
Notes
April 14, 2006
FN8101.1