MCP131X datasheet(22/44 Pages) MICROCHIP

22 / 44 page

MCP131X/2X

DS21985A-page 22

3.1

Ground Terminal (VSS)

VSS provides the negative reference for the analog

input voltage. Typically, the circuit ground is used.

3.2

Supply Voltage (VDD)

VDD can be used for power supply monitoring or a

voltage level that requires monitoring.

3.3

Reset Output (RST and RST)

There are four types of Reset output pins. These are:

Open-Drain active-low Reset, External pull-up

resistor required

Open-Drain active-low Reset, Internal pull-up

resistor

Push-Pull active-low Reset

Push-Pull active-high Reset

Some devices have both an active-low and active-high

Reset output.

3.3.1

ACTIVE-LOW (RST) - OPEN-DRAIN,

EXTERNAL PULL-UP RESISTOR

The RST open-drain output remains low while VDD is

below the Reset voltage threshold (VTRIP). Once the

device voltage (VDD) returns to a high level (VTRIP +

VHYS), the device will remain in Reset for the Reset

delay timer (TRST). After that time expires, the RST pin

will float, and an external pull-up resistor is required to

bring the output to the high state.

3.3.2

ACTIVE-LOW (RST) - OPEN-DRAIN,

INTERNAL PULL-UP RESISTOR

The RST open-drain output remains low while VDD is

below the Reset voltage threshold (VTRIP). Once the

device voltage (VDD) returns to a high level (VTRIP +

VHYS), the device will remain in Reset for the Reset

delay timer (TRST). After that time expires, the RST pin

will be pulled high by an internal pull-up resistor (typi-

cally 4.7 k

Ω).

3.3.3

ACTIVE-LOW (RST) - PUSH-PULL

The RST push-pull output remains low while VDD is

below the Reset voltage threshold (VTRIP). Once the

device voltage (VDD) returns to a high level (VTRIP +

VHYS), the device will remain in Reset for the Reset

delay timer (TRST). After that time expires, the RST pin

will be driven to the high state.

3.3.4

ACTIVE-HIGH (RST) - PUSH-PULL

The RST push-pull output remains high while VDD is

below the Reset voltage threshold (VTRIP). Once the

device voltage (VDD) returns to a high level (VTRIP +

VHYS), the device will remain in Reset for the Reset

delay timer (TRST). After that time expires, the RST pin

will be driven to the low state.

3.4

Manual Reset Input (MR)

The Manual Reset (MR) input pin allows a push button

switch to easily be connected to the system. When the

push button is depressed, it forces a system Reset.

This pin has circuitry that filters noise that may be

present on the MR signal.

The MR pin is active-low and has an internal pull-up

resistor.

3.5

Watchdog Input

In some systems, it is desirable to have an external

Watchdog Timer to monitor the operation of the sys-

tem. This is done by requiring the embedded controller

to “pet” the Watchdog Timer within a predetermined

time frame (TWD). If the MCP131X/2X is not “petted”

within this time frame, the MCP131X/2X will force the

Reset pin(s) active.

The embedded controller “pets” the MCP131X/2X by

forcing an edge transition on the WDI pin. The WDT

Timer is activated by the first falling edge on the WDI

pin.

The standard offering devices have a typical Watchdog

Timer period (TWD) of 1.6 s. Table 1-3 shows the avail-

able Watchdog Timer periods.

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