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 15 of 78
NXP Semiconductors
PCF8523
Real-Time Clock (RTC) and calendar
8.5 Power management functions
The PCF8523 has two power supply pins:
• V
DD
- the main power supply input pin
• V
BAT
- the battery backup input pin
The PCF8523 has two power management functions implemented:
• Battery switch-over function
• Battery low detection function
The power management functions are controlled by the control bits PM[2:0] in register
Control_3 (02h):
[1] When the battery switch-over function is disabled, the PCF8523 works only with the power supply V
DD
.
[2] When the battery switch-over function is disabled, the PCF8523 works only with the power supply V
DD
and
the battery low detection function is disabled. V
BAT
must be put to V
DD
.
[3] Default value.
8.5.1 Standby mode
When the device is first powered up from the battery (V
BAT
) but without a main supply
(V
DD
), the PCF8523 automatically enters the standby mode. In standby mode, the
PCF8523 does not draw any power from the backup battery until the device is powered up
from the main power supply V
DD
. Thereafter, the device switches over to battery backup
mode whenever the main power supply V
DD
is lost.
It is also possible to enter into standby mode when the chip is already supplied by the
main power supply V
DD
and a backup battery is connected. To enter the standby mode,
the power management control bits PM[2:0] have to be set logic 111. Then the main
power supply V
DD
must be removed. As a result of it, the PCF8523 enters the standby
mode and does not draw any current from the backup battery before it is powered up
again from main supply V
DD
.
Table 11. Power management function control bits
PM[2:0] Function
000 battery switch-over function is enabled in standard mode;
battery low detection function is enabled
001 battery switch-over function is enabled in direct switching mode;
battery low detection function is enabled
010,011
[1]
battery switch-over function is disabled - only one power supply (V
DD
);
battery low detection function is enabled
100 battery switch-over function is enabled in standard mode;
battery low detection function is disabled
101 battery switch-over function is enabled in direct switching mode;
battery low detection function is disabled
110 not allowed
111
[2][3]
battery switch-over function is disabled - only one power supply (V
DD
);
battery low detection function is disabled