TC1270AMAVRCTR datasheet(24/42 Pages) MICROCHIP

24 / 42 page

TC1270A/70AN/71A

DS20002035F-page 24

 2007-2022 Microchip Technology Inc. and its subsidiaries

5.6

Controllers and Processors With

Bidirectional I/O Pins

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 k

 resistor in series with the output of the

TC127XA (Figure 5-7). If there are other components

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:

Interfacing the TC1270A or

TC1271A Push-Pull Output to a Bidirectional

Reset I/O pin.

5.7

Migration Paths

Figure 5-8 shows the 5-pin SOT-23 footprint of the

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 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:

SOT-23 5-Pin to 3-Pin

Comparison.

5.8

Reset Signal Integrity During

Power-Down

The TC1270A and TC1271A Reset output is valid

down to VDD = 1.0V. Below this voltage the output

becomes 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 volt-

age. However, in situations where the Reset signal

must be maintained valid to VDD = 0V, external circuitry

is 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 (Figure 5-9).

Similarly for devices where the Reset signal is

active-high, a pull-up resistor to VDD is required to

ensure a valid high RST signal for VDD below 1.0V

(Figure 5-10).

This resistor value, though not critical, should be

chosen such that it does not appreciably load the Reset

pin under normal operation (100 k

 should be suitable

for most applications).

FIGURE 5-9:

Ensuring a Valid Active-Low

Reset Pin Output State as VDD Approaches 0V.

FIGURE 5-10:

Ensuring a Valid Active-High

Reset Pin Output State as VDD Approaches 0V.

VSS

VDD

RST

Reset I/O

TC1270A/71A

VDD

RST

Buffered

Reset to

system

4.7 k



SOT-23-3

SOT-23-5

VDD

RST

VSS

VDD

RST

VSS

VDD

RST

TC1270A

VDD

100 k



VSS

VDD

RST

TC1271A

VDD

100 k



TC1270AMAVRCTR 数据表(PDF) 24 Page - Microchip Technology

TC1270AMAVRCTR 数据表(HTML) 24 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

数据表下载