PCF2129AT NXP [NXP Semiconductors], PCF2129AT Datasheet - Page 18

• Manufacturer Part Number: PCF2129AT
• Description: Integrated RTC, TCXO and quartz crystal
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCF2129A_1
Product data sheet
8.5.3 Battery low detection function
The output pin BBS can be used as a supply for battery backup devices such as SRAM
(see
V
The PCF2129A has a battery low detection circuit which monitors the status of the battery
V
When V
(register Control_3) is set to indicate that the battery is low and that it must be replaced. A
low battery will not ensure data integrity during periods of backup battery operation.
Monitoring of the battery voltage also occurs during battery operation.
When V
Figure
1. The battery low flag BLF is set logic 1.
2. An interrupt is generated if the control bit BLIE (register Control_3) is enabled
3. The flag BLF remains logic 1 until the battery is replaced. BLF cannot be cleared
Fig 8.
BBS
BAT
V
DD
V
(see
using the interface. It is cleared automatically by the battery low detection circuit when
the battery is replaced.
(= 2.5 V)
th(bat)low
.
Ref. 3
= V
is driven from V
V
8):
BLF
BBS
BAT
INT
BAT
BAT
Section
Battery low detection behavior with bit BLIE logic 1 (enabled)
“AN10857”). For this case,
drops below the threshold value V
drops below the threshold value V
8.12.7).
DD
Rev. 01 — 13 January 2010
.
Figure 7
internal power supply (= V
th(bat)low
Integrated RTC, TCXO and quartz crystal
th(bat)low
shows the typical driving capability when
V
BAT
, the following sequence occurs (see
(typically 2.5 V) the BLF flag
BBS
)
PCF2129A
© NXP B.V. 2010. All rights reserved.
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