PCF2129T Datasheet, PDF (16/73 Pages) NXP Semiconductors – Accurate RTC with integrated quartz crystal for industrial

NXP Semiconductors
PCF2129T
Accurate RTC with integrated quartz crystal for industrial
When a power failure condition occurs and the power supply switches to the battery, the
following sequence occurs:
1. The battery switch flag BF (register Control_3) is set logic 1.
2. An interrupt is generated if the control bit BIE (register Control_3) is enabled
(see Section 8.12.6).
3. If the control bit BTSE (register Control_3) is logic 1, the timestamp registers store the
time and date when the battery switch occurred (see Section 8.11.4).
4. The battery switch flag BF is cleared by command; it must be cleared to clear the
interrupt.
The interface is disabled in battery backup operation:
• Interface inputs are not recognized, preventing extraneous data being written to the
device
• Interface outputs are high-impedance
8.5.1.1 Standard mode
If V_DD > V_BAT OR V_DD > V_th(sw)bat, the internal power supply is V_DD.
If V_DD < V_BAT AND V_DD < V_th(sw)bat, the internal power supply is V_BAT.
backup battery operation
V_DD
V_BBS
V_BAT
internal power supply (= V_BBS)
V_BBS
V_th(sw)bat
(= 2.5 V)
V_DD (= 0 V)
BF
INT
cleared via interface
001aaj311
Fig 4.
V_th(sw)bat is the battery switch threshold voltage. Typical value is 2.5 V. In standard mode, the
battery switch-over works only for V_DD > 2.5 V.
V_DD may be lower than V_BAT (for example V_DD = 3 V, V_BAT = 4.1 V).
Battery switch-over behavior in standard mode with bit BIE set logic 1 (enabled)
8.5.1.2 Direct switching mode
If V_DD > V_BAT the internal power supply is V_DD.
If V_DD < V_BAT the internal power supply is V_BAT.
PCF2129T
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 12 February 2013
© NXP B.V. 2013. All rights reserved.
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