TC1270A MICROCHIP [Microchip Technology], TC1270A Datasheet - Page 21

• Manufacturer Part Number: TC1270A
• Description: Voltage Supervisor with Manual Reset Input
• Manufacturer: MICROCHIP [Microchip Technology]

4.3
The minimum pulse width (time) required to cause a
Reset may be an important criteria in the implementa-
tion of a Power-on Reset (POR) circuit. This time is
referred to as transient duration. The TC127XA devices
are designed to reject a level of negative-going
transients (glitches) on the power supply line.
Transient duration is the amount of time needed for
these supervisory devices to respond to a drop in V
The transient duration time (t
magnitude of V
of duration and overdrive that lies under the
duration/overdrive curve will not generate a Reset
signal. Generally speaking, the transient duration time
decreases with an increase in the V
Figure 4-9
Reset comparator overdrive. It shows that the farther
below the trip point the transient pulse goes, the
duration of the pulse required to cause a Reset gets
shorter. So any combination of duration and overdrive
that lays under the curve will not generate a Reset
signal. Combinations above the curve are detected as
a brown-out or power-down.
Transient immunity can be improved by adding a
bypass capacitor (typically 0.1 µF) as close as possible
to the V
FIGURE 4-9:
Transient Duration Waveform.
© 2007 Microchip Technology Inc.
5V
0V
DD
Negative Going V
Transient Overdrive Voltage (mV)
pin of the TC127XA device.
shows an example transient duration vs.
Area above curve will
generate a reset signal
TRIP
Area below curve will
not generate a reset signal
– V
Time (µs)
Example of Typical
DD
(overdrive). Any combination
t
V
TRAN
(Overdrive)
TRAN
TRIP(MIN)
DD
) is dependent on the
(Duration)
TRIP
Transients
- V
– V
DD
V
V
DD
TRIP(MAX)
TRIP(MIN)
voltage.
DD
.
4.4
The Manual Reset input pin (MR) allows the Reset pins
(RST/RST) to be manually forced to their active states.
The MR pin has circuitry to filter noise pulses that may
be present on the pin.
diagram for using the TC127XA with a push button
switch. To minimize the required external components,
the MR input has an internal pull-up resistor.
A mechanical push button or active logic signal can
drive the MR input.
Once MR has been low for a time, t
Reset delay time), the Reset output pins are forced
active. The Reset output pins will remain in their active
states for the Reset delay timer time out period (t
Figure 4-11
switch input and the Reset pins output.
FIGURE 4-10:
FIGURE 4-11:
4.4.1
The noise filter filters out noise spikes (glitches) on the
Manual Reset pin (MR). Noise spikes less than 100 ns
(typical) are filtered.
MR
RST
RST
TC1270A/70AN/71A
The MR input typically ignores input pulses
of 100 ns.
Manual Reset with Glitch Filter
Circuit
NOISE FILTER
V
shows a waveform for the Manual Reset
IL
MR
t
MD
TC127XA
V
+5V
V
DD
t
SS
MR
Push Button Reset.
MR Input – Push Button.
RST
Figure 4-10
V
MCLR
IH
DS22035B-page 21
t
RST
PIC
MD
shows a block
(the Manual
®
MCU
RST
).