Datasheet

PCF2127AT All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 6 — 11 July 2013 18 of 86
NXP Semiconductors
PCF2127AT
Integrated RTC, TCXO and quartz crystal
8.6 Power management functions
The PCF2127AT has two power supply pins and one power output pin:
• V
DD
- the main power supply input pin
• V
BAT
- the battery backup input pin
• BBS - battery backed output voltage pin (equal to the internal power supply)
The PCF2127AT has three power management functions implemented:
• Battery switch-over function
• Battery low detection function
• Extra power fail detection function
The power management functions are controlled by the control bits PWRMNG[2:0] in
register Control_3:
[1] Default value.
[2] When the battery switch-over function is disabled, the PCF2127AT works only with the power supply V
DD
;
V
BAT
must be put to ground and the battery low detection function is disabled.
Table 18. Power management control bit description
PWRMNG[2:0] Function
000
[1]
battery switch-over function is enabled in standard mode;
battery low detection function is enabled;
extra power fail detection function is enabled
001 battery switch-over function is enabled in standard mode;
battery low detection function is disabled;
extra power fail detection function is enabled
010 battery switch-over function is enabled in standard mode;
battery low detection function is disabled;
extra power fail detection function is disabled
011 battery switch-over function is enabled in direct switching mode;
battery low detection function is enabled;
extra power fail detection function is enabled
100 battery switch-over function is enabled in direct switching mode;
battery low detection function is disabled;
extra power fail detection function is enabled
101 battery switch-over function is enabled in direct switching mode;
battery low detection function is disabled;
extra power fail detection function is disabled
110
[2]
battery switch-over function is disabled - only one power supply (V
DD
);
battery low detection function is disabled;
extra power fail detection function is enabled
111
[2]
battery switch-over function is disabled - only one power supply (V
DD
);
battery low detection function is disabled;
extra power fail detection function is disabled