Datasheet

 2005-2012 Microchip Technology Inc. DS21985D-page 31
MCP131X/2X
4.1.1 POWER-UP/RISING V
DD
As the device V
DD
rises, the device’s Reset circuit will
remain active until the voltage rises above the “actual”
trip point (V
TRIP
) plus the hysteresis (V
HYS
).
Figure 4-13 shows a power-up sequence and the
waveform of the RST and RST pins.
As the device powers up, the voltage will start below
the valid operating voltage of the device. At this
voltage, the Reset output value is not valid. Once the
voltage is above the minimum operating voltage (1V)
and below the selected V
TRIP
, the Reset output will be
active.
Once the device voltage rises above the “actual” trip
point (V
TRIP
) plus the hysteresis (V
HYS
), the Reset delay
timer (t
RST
) starts. When the Reset delay timer times
out, the Reset output (RST/RST
) is driven inactive.
FIGURE 4-13: Reset Pin Operation on a
Power-up.
4.1.2 POWER-DOWN/BROWN-OUTS
As the device powers-down/brown-outs, the voltage
(V
DD
) falls from a voltage above the device’s trip point
(V
TRIP
). The device’s “actual” trip point voltage (V
TRIP
)
will be between the minimum trip point (V
TRIPMIN
) and
the maximum trip point (V
TRIPMAX
). Once the device
voltage (V
DD
) goes below this voltage, the Reset pin(s)
will be forced to the active state. There is a hysteresis
on this trip point. This is so noise on the device voltage
(V
DD
) does not cause the Reset pin (RST/RST) to
“jitter” (change between driving an active and inactive).
Figure 4-14 shows the waveform of the RST pin as
determined by the V
DD
voltage, while Tabl e 4- 1 shows
the state of the RST
pin.
4.1.2.1 Operation of RST pin with Internal
Pull-Up Resistor
The internal pull-up resistor has a typical value of
4.7 k. The internal pull-up eliminates the need for an
external resistor.
To reduce the current consumption of the device, when
the RST
pin is driving low, the resistor is disconnected.
FIGURE 4-14: RST Operation as Determined by the V
TRIP
and V
HYS
.
Note: While the Reset delay timer (t
RST
) is
active, additional system current is
consumed.
V
TRIPMAX
V
TRIPMIN
V
TRIP
1V
V
DD
V
TRIP
+ V
HYS
t
RST
RST
RST
Note: Only the MCP1316M, MCP1318M and
MCP1319M devices have an open-drain
RST
output pin with an internal pull-up
resistor.
V
DD
V
TRIPMAX
V
TRIPMIN
V
TRIP
V
TRIP
V
TRIP
+ V
HYS
RST
1V
< 1V is outside the
device specifications
t
RPD
t
RST
t
RPD
t
RST