TC1270A MICROCHIP [Microchip Technology], TC1270A Datasheet - Page 25

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

5.6
Some microcontrollers have bidirectional Reset pins.
Depending on the current drive capability of the
controller pin, an indeterminate logic level may result if
there is a logic conflict. This can be avoided by adding
a 4.7 kΩ resistor in series with the output of the
TC127XA
in the system that require a Reset signal, they should
be buffered so as not to load the Reset line. If the other
components are required to follow the Reset I/O of the
microcontroller, the buffer should be connected as
shown with the solid line.
FIGURE 5-7:
TC1271A Push-Pull Output to a Bidirectional
Reset I/O pin.
5.7
Figure 5-8
TC1270A, TC1270AN and TC1271A devices. Devices
that are in the 3-pin SOT-23 package could be used in
that circuit with the loss of the Manual Reset
functionality. Examples of compatible footprint devices
in the SOT-23-3 package are the MCP111, MCP112,
TC54, and TC51 devices. This allows the system to be
designed to offer a “base” functionality and a higher
end system with the “enhanced” functionality, which
includes a manual reset.
FIGURE 5-8:
Comparison.
© 2007 Microchip Technology Inc.
V
V
MR
NC
DD
DD
TC1270A/71A
MR
1
2
3
Controllers and Processors With
Bidirectional I/O Pins
Migration Paths
SOT-23-5
V
V
(Figure
SS
DD
shows the 5-pin SOT-23 footprint of the
RST
or
RST
5
4
5-7). If there are other components
V
RST
or
RST
SS
4.7 kΩ
Interfacing the TC1270A or
SOT-23 5-pin to 3-pin
V
Reset I/O
DD
V
V
3
SS
SOT-23-3
DD
Buffered
Reset to
system
1
2
V
RST
or
RST
SS
5.8
The TC1270A and TC1271A reset output is valid down
to V
an “open circuit” and does not sink current. This means
CMOS logic inputs to the Microcontroller will be floating
at an undetermined voltage. Most digital systems are
completely shut down well above this voltage.
However, in situations where the Reset signal must be
maintained valid to V
required.
For devices where the Reset signal is active-low, a
pull-down resistor must be connected from the
TC1270A RST pin to ground to discharge stray
capacitances and hold the output low
Similarly for devices where the Reset signal is
active-high, a pull-up resistor to V
ensure a valid high RST signal for V
(Figure
This resistor value, though not critical, should be
chosen such that it does not appreciably load the Reset
pin under normal operation (100 kΩ will be suitable for
most applications).
FIGURE 5-9:
Reset pin output state as V
FIGURE 5-10:
Reset pin output state as V
TC1270A/70AN/71A
DD
= 1.0V. Below this voltage the output becomes
5-10).
Reset Signal Integrity During
Power-Down
MR
MR
TC1270A
TC1271A
V
V
V
V
V
V
DD
SS
DD
DD
SS
DD
Ensuring a valid active-low
Ensuring a valid active-high
DD
RST
RST
= 0V, external circuitry is
DD
DD
approaches 0V.
approaches 0V.
R
100 kΩ
DD
DS22035B-page 25
R
100 kΩ
1
(Figure
1
DD
is required to
below 1.0V
5-9).