TC1270ASVRCTR datasheet(17/40 Pages) MICROCHIP

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DS22035B-page 17

TC1270A/70AN/71A

4.0

DEVICE OPERATION

4.1

General Description

For many of today’s microcontroller applications, care

must be taken to prevent low-power conditions that can

cause many different system problems. The most

common causes are brown-out conditions, where the

system supply drops below the operating level

momentarily. The second most common cause is when

a slowly decaying power supply causes the microcon-

troller to begin executing instructions without sufficient

voltage to sustain volatile memory (RAM), thus

producing indeterminate results.

The TC127XA family (TC1270A, TC1270AN, and

TC1271A)

are

cost-effective

voltage

supervisor

devices designed to keep a microcontroller in Reset

until the system voltage has reached and stabilized at

the proper level for reliable system operation. These

devices also operate as protection from brown-out

conditions when the system supply voltage drops

below a safe operating level.

A Manual Reset input (MR pin) is provided. This allows

a push button switch to be directly connected to the

TC127XA device, and is suitable for use as a push

button Reset. This allows the system to easily be reset

from the external control of the push button switch. No

external components are required.

The Reset pin (RST or RST) will be forced active, if any

of the following occur:

• During device power up

•VDD goes below the device threshold voltage

• The Manual Reset input (MR) goes low

Figure 4-1 shows a high level block diagram of the

devices. The device can be described with three

functional blocks. These are:

• Voltage Detect circuit

• Manual Reset with Glitch Filter circuit

• Reset Generator circuit

The Reset Generator circuit controls the reset delay

time of the reset output signal.

There are three Reset Delay time options. Depending

on the option, the reset signal (RST/RST pin) will be

held active for a minimum of 1.09 ms, 17.5 ms, or

140 ms.

The TC1271A has an active-high RST output while the

TC1270A and TC1270AN have an active-low RST

output.

The TC1270A and TC1271A have a push-pull output

driver, while the TC1270AN has an open-drain output.

Figure 4-2 shows a typical circuit for a push-pull device

and Figure 4-3 shows a typical circuit for an open-drain

device.

FIGURE 4-1:

TC127XA High Level Block

Diagram.

FIGURE 4-2:

Typical Push-Pull

Application Circuit.

FIGURE 4-3:

Typical Open-Drain

Application Circuit.

The TC1270A and TC1271A devices are available in a

4-Pin SOT-143 package to maintain footprint compati-

bility with the TC1270, TC1271, TCM811, and TCM812

devices, and the SOT-23-5 package. The TC1270AN is

only available in the SOT-23-5 package.

Low supply current makes these devices suitable for

battery powered applications.

Device specific block diagrams are shown in Figure 4-4

through Figure 4-6.

VDD

RST

Voltage

Detector

Reset

Circuit

Manual Reset

with Glitch

Filter Circuit

Generator

Circuit

VRST

MRRST

Push

Button

VSS

VDD

Reset Input

TC1270A/1A

VDD

0.1 µF

RST

Push

Button

VSS

VDD

RST

Reset Input

TC1270AN

VDD

0.1 µF

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