Datasheet

 2010-2013 Microchip Technology Inc. DS20002266E-page 27
MCP79410/MCP79411/MCP79412
FIGURE 8-5: MFP FUNCTIONAL BLOCK DIAGRAM
8.6 Battery Backed Operation
The MCP7941X features an internal power switch that
can power the clock and the SRAM in the event that
the VCC supply is not available. The voltage applied to
the V
BAT pin serves as the backup supply. To enable
the external battery switchover operation, bit 3
VBATEN (Day Register) must be set. Setting this bit
enables the path from the V
BAT pin to the internal
power switch.
A 1K series resistor is recommended between the
external battery and the V
BAT pin to limit the current to
the internal switch circuit. Additionally, an 100 pF
capacitor is required between the VBAT pin and VSS.
This is shown in Figure 1-1.
The V
TRIP is the voltage at which the internal switch
operates the device from the V
BAT supply. When it falls
below V
TRIP, the system will continue to operate the
RTCC and SRAM using the V
BAT supply. When VCC is
above V
TRIP the device is operated using the main
supply. The following conditions apply:
If the battery backup feature is not being used, the
V
BAT pin should be connected to GND.
For more information on V
BAT conditions, see AN1365,
“RTCC Best Practices”.
1
0
1
0
1
0
VSS
Oscillator
SQWE
X1
X2
ALM0IF
ALM1IF
ALM0POL
ALM1POL
OUT
MFP
Pin
Postscaler
32.768 kHz
8.192 kHz
4.096 kHz
1Hz
64Hz
(Digital Cal)
RS2:0
011
010
001
000
1xx
MUX
TABLE 8-2: MFP FUNCTION WITH SUPPLY
Supply
Condition
Read/Write
Access
Powered
By
CLKOUT Alarms
Time
Keeping
V
CC < VTRIP No VBAT No Yes Yes
VCC > VTRIP Yes VCC Yes Yes Yes