X1205V8IZT1
| Model | X1205V8IZT1 |
| Description | 2-Wire RTC Real Time Clock/Calendar |
| PDF file | Total 22 pages (File size: 329K) |
| Chip Manufacturer | INTERSIL |
X1205
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 supercapacitor, which is
connected to the Vback pin. Do not use the diode to
charge a battery (especially lithium batteries!).
Figure 13. Supercapactor charging circuit
2.7-5.5V
V
CC
V
back
Supercapacitor
V
SS
Since the battery switchover occurs at Vcc=Vback-
0.1V (see Figure 13), 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 6:
Table 6. Battery Backup Operation
1. Example Application, Vcc=5V, Vback=3.0V
Condition
a. Normal Operation
b. Vcc on with no battery
c. Backup Mode
Vcc
5.00
5.00
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
a. Normal Operation
b. Vcc on with no battery
c. Backup Mode
d. UNWANTED - Vcc ON, Vback powering
Vcc
3.30
3.30
0-1.8
2.65 - 3.30
Vback
3.00
0
1.8-3.0*
> Vcc
Vtrip
2.65
2.65
2.65
2.65
Iback
<<1µA
0
<2µA*
up to 3mA
Timekeeping only
Internal Vcc=Vback
*since Vback>2.65V is higher than Vtrip, the battery is powering the entire device
19
FN8097.2
September 23, 2005
