MCP79520-ISLASHMS datasheet(33/58 Pages) MICROCHIP

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DS20002300D-page 33

MCP7951X/MCP7952X

5.7

Battery Backup

The MCP795XX features a backup power supply input

(VBAT) that can be used to provide power to the

timekeeping circuitry, RTCC registers and SRAM while

primary power is unavailable. The MCP795XX will

automatically switch to backup power when VCC falls

below VTRIP and back to VCC when it is above VTRIP.

The VBATEN bit must be set to enable the VBAT input.

The following functionality is maintained while

operating on backup power:

• Timekeeping

• Alarms

• Alarm Outputs

• Digital Trimming

• RTCC Register and SRAM Contents

The following features are not available while operating

on backup power:

• SPI Communication

• Watchdog Timer

• Event Detect

• Square Wave Clock Output

5.7.1

POWER-FAIL TIMESTAMP

The MCP795XX includes a power-fail timestamp

module that stores the minutes, hours, date and month

when primary power is lost and when it is restored

(Figure 5-9). The PWRFAIL bit is also set to indicate

that a power failure occurred.

To utilize the power-fail timestamp feature, a backup

power supply must be available with the VBAT input

enabled, and the oscillator should also be running to

ensure accurate functionality.

5.7.1.1

Configuring Battery Backup

In order to configure the battery backup feature, the

following steps need to be performed:

Enable the oscillator.

Wait for the OSCRUN bit to be set, indicating the

oscillator has started.

Enable battery backup by setting the VBATEN

bit.

FIGURE 5-9:

POWER-FAIL TIMESTAMP TIMING

Note:

If VCC is lost while VBAT voltage is applied,

but where VBATEN is not set to ‘1’, it

could result in undetermined behavior. If a

backup supply is not used, the VBAT pin

should be connected to VSS.

Note:

Throughout this section, references to the

Timestamp module are referred to

generically by the use of ‘x’ in place of the

specific

module

name.

Thus,

“PWRxxMIN” might refer to the minutes

Note 1: The PWRFAIL bit must be cleared to log

new timestamp data. This is to ensure

previous timestamp data is not lost.

2: Clearing the PWRFAIL bit will clear all

timestamp registers.

Power-Down

Power-Up

Timestamp

VCC

VTRIP

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