x1205s8izt1 Intersil Corporation, x1205s8izt1 Datasheet - Page 20

• Manufacturer Part Number: x1205s8izt1
• Description: 2-wire? Rtc Real Time Clock/calendar
• Manufacturer: Intersil Corporation

Referring to Figure 13, Vtrip applies to the “Internal
Vcc” node which powers the entire device. This means
that if Vcc is powered down and the battery voltage at
Vback is higher than the Vtrip voltage, then the entire
chip will be running from the battery. If Vback falls to
lower than Vtrip, then the chip shuts down and all out-
puts are disabled except for the oscillator and time-
keeping circuitry. The fact that the chip can be
powered from Vback is not necessarily an issue since
standby current for the RTC devices is <2µA for this
mode (called “main timekeeping current” in the data
sheet). Only when the serial interface is active is there
an increase in supply current, and with Vcc powered
down, the serial interface will most likely be inactive.
One way to prevent operation in battery backup mode
above the Vtrip level is to add a diode drop (silicon
diode preferred) to the battery to insure it is below
Vtrip. This will also provide reverse leakage protection
which may be needed to get safety agency approval.
One mode that should always be avoided is the opera-
tion of the RTC device with Vback greater than both Vcc
and Vtrip (Condition 2d in Table 6). This will cause the
battery to drain quickly as serial bus communication and
non-volatile writes will require higher supplier current.
20
X1205
PERFORMANCE DATA
Figure 14. I
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
BACK
-40
Multi-Lot Process Variation Data
Performance
I
BACK
Temperature °C
25
vs. Temperature
60
3.3V
September 23, 2005
1.8V
85
FN8097.2