TC1270AMAVRCTR datasheet(17/42 Pages) MICROCHIP

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DS20002035F-page 17

TC1270A/70AN/71A

FIGURE 4-4:

TC1270A Block Diagram.

FIGURE 4-5:

TC1270AN Block Diagram.

FIGURE 4-6:

TC1271A Block Diagram.

4.2

Voltage Detect Circuit

The voltage detect circuit monitors VDD. The device’s

Reset voltage trip point (VTRIP) is selected when the

device is ordered. The voltage on the device’s VDD pin

determines the output state of the RST/RST pin.

VDD voltages above the VTRIP(MAX) force the RST/RST

pin inactive. VDD voltages below the VTRIP(MIN) force

the RST/RST pin active. The state of the RST/RST pin

is unknown for VDD voltages between VTRIP(MAX) and

VTRIP(MIN). This is shown in Table 4-1

TABLE 4-1:

VDD LEVELS TO RST/RST

OUTPUT STATES

The term VTRIP will be used as the general term for the

trip point voltage where the device actually trips.

In the case where VDD is falling (for voltages starting

above VTRIP(MAX)):

• Voltages above VTRIP(MAX) will never cause the

RST/RST output pin to be driven active.

• Voltages below VTRIP(MIN) will always cause the

RST/RST output pin to be driven active.

In the case where VDD is rising (for voltages starting

below VTRIP(MIN)):

• Voltages above VTRIP(MAX) will always cause the

RST/RST output pin to be driven inactive, (or

floated, in the TC1270AN) after the Reset Delay

Timer (tRST), times out.

Table 4-2 shows the various device trip point options

and their VTRIP(MAX) and VTRIP(MIN) voltages. The neg-

ative percentage change from common regulated

voltages is also shown.

If the VDD is falling from the regulated voltage as it

crosses the VTRIP voltage, the RST/RST pin is driven

active. Then, the desired circuitry is forced into Reset,

or the circuitry has the indication that the VDD is below

the selected VTRIP.

VDD

Comparator

–

Output

Driver

RST

Reference

Noise Filter

Voltage

Delay

(Push-

Pull)

VDD

Comparator

–

RST

Reference

VSS

Noise Filter

Voltage

Delay

Output

Driver

(Open-

Drain)

VDD

Comparator

–

RST

Reference

Noise Filter

Voltage

Delay

Output

Driver

(Push-

Pull)

VDD Voltage Level

Output State

RST

VDD  VTRIP(MAX)

H(1, 2)

L(1)

VTRIP(MIN) < VDD < VTRIP(MAX)

VDD  VTRIP(MIN)

Legend: H = Driven HighL = Driven Low

U = Unknown, driven either High or Low

Note 1: The RST/RST pin will be driven inactive

after the Reset Delay Timer (tRST) times

out.

2: The TC1270AN RST pin will be floated

after the Reset Delay Timer (tRST) times

out.

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