X1226 datasheet(21/24 Pages) XICOR

21 / 24 page

X1226

REV 1.1.24 1/13/03

Characteristics subject to change without notice.

21 of 24

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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 8). This will cause

the battery to drain quickly as serial bus communica-

tion and non-volatile writes will require higher supplier

current.

PERFORMANCE DATA

IBACK Performance

1.4

1.2

1.0

0.8

0.6

0.4

0.2

IBACK vs. Temperature

Multi-Lot Process Variation Data

Temperature °C

-40

3.3V

1.8V

X1226 Datasheet(PDF) 21 Page - Xicor Inc.