X1228S14IZ Intersil, X1228S14IZ Datasheet - Page 26

• Manufacturer Part Number: X1228S14IZ
• Description: IC RTC/CAL/SUP/ALRM 4K EE 14SOIC
• Manufacturer: Intersil
• Type: Clock/Calendar/EEPROMr

Specifications of X1228S14IZ

• Memory Size: 4K (512 x 8)
• Time Format: HH:MM:SS (12/24 hr)
• Date Format: YY-MM-DD-dd
• Interface: I²C, 2-Wire Serial
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 8. 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
26
2.65 - 3.30
0-1.8
0-1.8
5.00
5.00
3.30
3.30
Vcc
Vcc
1.8-3.0*
Vback
1.8-3.0
Vback
> Vcc
X1228
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. A second consideration
is the trip point setting for the system RESET- func-
tion, known as Vtrip. Vtrip is set at the factory at levels
for systems with either Vcc = 5V or 3.3V operation,
with the following standard options:
V
V
V
V
The summary of conditions for backup battery opera-
tion is given in Table 8:
TRIP
TRIP
TRIP
TRIP
2.7-5.5V
Vtrip
Vtrip
4.38
4.38
4.38
2.65
2.65
2.65
2.65
= 4.63V ± 3%
= 4.38V ± 3%
= 2.85V ± 3%
= 2.65V ± 3%
up to 3mA
<<1µA
<<1µA
V
Iback
Iback
<2µA*
<2µA
CC
0
0
V
SS
V
back
Reset
Reset
H
H
H
H
H
L
L
Timekeeping
Timekeeping
Vcc=Vback
Supercapacitor
Internal
Notes
only
only
May 18, 2006
FN8100.4