Datasheet

 2005-2012 Microchip Technology Inc. DS21985D-page 25
MCP131X/2X
3.1 Ground Terminal (V
SS
)
V
SS
provides the negative reference for the analog
input voltage. Typically, the circuit ground is used.
3.2 Supply Voltage (V
DD
)
V
DD
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:
1. Open-Drain active-low Reset, External pull-up
resistor required
2. Open-Drain active-low Reset, Internal pull-up
resistor
3. Push-Pull active-low Reset
4. 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 V
DD
is
below the Reset voltage threshold (V
TRIP
). Once the
device voltage (V
DD
) returns to a high level
(V
TRIP
+V
HYS
), the device will remain in Reset for the
Reset delay timer (T
RST
). 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 V
DD
is
below the Reset voltage threshold (V
TRIP
). Once the
device voltage (V
DD
) returns to a high level
(V
TRIP
+V
HYS
), the device will remain in Reset for the
Reset delay timer (T
RST
). After that time expires, the
RST
pin will be pulled high by an internal pull-up
resistor (typically 4.7 k).
3.3.3 ACTIVE-LOW (RST) – PUSH-PULL
The RST push-pull output remains low while V
DD
is
below the Reset voltage threshold (V
TRIP
). Once the
device voltage (V
DD
) returns to a high level
(V
TRIP
+V
HYS
), the device will remain in Reset for the
Reset delay timer (T
RST
). 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 V
DD
is
below the Reset voltage threshold (V
TRIP
). Once the
device voltage (V
DD
) returns to a high level
(V
TRIP
+V
HYS
), the device will remain in Reset for the
Reset delay timer (T
RST
). 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
system. This is done by requiring the embedded
controller to “pet” the Watchdog Timer within a
predetermined time frame (T
WD
). 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 (T
WD
) of 1.6 s. Table 1-3 shows the
available Watchdog Timer periods.