BQ32000 Datasheet, PDF (6/20 Pages) Texas Instruments – REAL-TIME CLOCK (RTC)

bq32000
SLUS900B – DECEMBER 2008 – REVISED JUNE 2009................................................................................................................................................... www.ti.com
V_BACK Switchover
The bq32000 has an internal switchover circuit that causes the device to switch from main power supply to
backup power supply when the voltage of the main supply pin V_CC drops below a minimum threshold. The V_BACK
switchover circuit uses an internal reference voltage V_REF derived from the on-chip bandgap reference; V_REF is
approximately 2.8 V. The device switches to the V_BACK supply when V_CC is less than the lesser of V_BACK or V_REF.
Similarly, the device switches to the V_CC supply when V_CC is greater than either V_BACK or V_REF.
V_BACK > V_REF
V_BACK > V_REF
3.3V
VB AC K
V_{R E F}
V_CC
V_CC
–5 V/ms (max)
3.3V
VB AC K
V_{R E F}
T ime
Time
On VCC
On V BAC K
On V BAC K
On VCC
V_REF > V_BACK
3.3V
V_{R E F}
V_CC
V_{B AC K}
–5 V/ms (max)
T ime
V_REF > V_BACK
V_CC
3.3V
V_{R E F}
V_{B AC K}
Time
On VCC
On V BAC K
On V BAC K
Figure 2. Switchover Diagram
On VCC
6
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