Datasheet

PCF8523 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 6 — 17 September 2013 53 of 78
NXP Semiconductors
PCF8523
Real-Time Clock (RTC) and calendar
14. Application information
14.1 Battery switch-over applications
The functionality of the battery switch-over is limited by the fact that the power supply V
DD
is monitored every 1 ms in order to save power consumption. Considering further that the
battery switch-over threshold value (V
th(sw)bat
) is typically 2.5 V, the power management
operating limit (V
DD(min)
) is 1.8 V, and that V
DD
is monitored every 1 ms, the battery
switch-over works properly in all cases where V
DD
falls with a rate lower than 0.7 V/ms, as
shown in Figure 36
:
In an application, where during power-down, the current consumption on pin V
DD
is
• in the range of a few A a capacitor of 100 nF on pin V
DD
is enough to allow a slow
power-down and the proper functionality of the battery switch-over
3
Fig 35. I
2
C-bus timing diagram; rise and fall times refer to 30 % and 70 %
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Fig 36. Supply voltage with respect to sampling and comparing rate
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