MCP7940N-ESLASHST datasheet(15/42 Pages) MICROCHIP

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 2011-2013 Microchip Technology Inc.

DS25010E-page 15

MCP7940N

5.2.2

MFP

Pin 7 is a multi-function pin and supports the following

functions:

• Use of the OUT bit in the Control register for

single bit I/O

• Alarm Outputs – Available in VBAT mode

• FOUT mode – driven from a FOSC divider – Not

available in VBAT mode

The internal control logic for the MFP is connected to

the switched internal supply bus, this allows operation

in VBAT mode. The Alarm Output is the only mode that

operates in VBAT mode, other modes are suspended.

5.2.3

VBAT

The MCP7940N features an internal switch that will

power the clock and the SRAM. In the event that the

VCC supply is not available, the voltage applied to the

VBAT pin serves as the backup supply. A low-value

series resistor is recommended between the external

battery and the VBAT pin to limit the current to the

internal switch circuit.

The VBAT trip point is the point at which the internal

switch operates the device from the VBAT supply and

is typically 1.5V (VTRIP specification D12) typical.

When VDD falls below 1.5V the system will continue to

operate the RTCC and SRAM using the VBAT supply.

The following conditions apply:

If the VBAT feature is not being used, the VBAT pin must

be connected to GND. For more information on VBAT

conditions see application note AN1365, “RTCC Best

Practices” (DS01365).

TABLE 5-2:

Supply

Condition

Read/Write

Access

Powered

VCC < VTRIP, VCC < VBAT

VBAT

VCC > VTRIP, VCC < VBAT

Yes

VCC

VCC > VTRIP, VCC > VBAT

Yes

VCC

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