TC1272ARVNBTR View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

TC1272ARVNBTR

3-Pin Reset Monitor

Microchip Technology 

TC1272A

3.0 APPLICATIONS INFORMATION

3.1 VDD Transient Rejection

The TC1272A provides accurate VDD monitoring and

reset timing during power-up, power-down and brown-

out/sag conditions. These devices also reject negative-

going transients (glitches) on the power supply line.

Figure 3-1 shows the maximum transient duration vs.

maximum negative excursion (overdrive) for glitch

rejection. Any combination of duration and overdrive

that lies under the curve will not generate a reset

signal.

VDD

VTH

Overdrive

Duration

400

TA = +25°C

320

240

160

TC1272A/L/M/J

80

0 TC1272A/Z/R/S/T

1

5

100

1000

Reset Comparator Overdrive

[VTH - VDD] (mv)

130

120

110

100

90

80

70

60

50

40

30

1

TC1272A/L/M/J

TC1272A/Z/R/S/T

10

100

Reset Comparator Overdrive (mV)

1000

[VTH - VDD] (mv)

FIGURE 3-1:

Maximum Transient

Duration vs. Overdrive for Glitch Rejection at

+25°C.

Combinations above the curve are detected as a

brown-out or power-down condition. Transient immu-

nity can be improved by adding a capacitor in close

proximity to the VDD pin of the TC1272A.

3.2 RESET Signal Integrity During

Power-Down

The TC1272A RESET output is valid to VDD = 1.0V.

Below this voltage, the output becomes an "open cir-

cuit" and does not sink current. This means CMOS

logic inputs to the microcontroller will be floating at an

undetermined voltage. Most digital systems are com-

pletely shut down well above this voltage. However, in

situations where RESET must be maintained valid to

VDD = 0V, a pull-down resistor must be connected from

RESET to ground to discharge stray capacitances and

hold the output low (Figure 3-2). This resistor value,

though not critical, should be chosen such that it does

not appreciably load RESET under normal operation

(100 kΩ will be suitable for most applications).

VDD

VDD

TC1272A

RESET

GND

R1

100 kΩ

FIGURE 3-2:

The addition of R1 at the

RESET output of the TC1272A ensures that the

RESET output is valid to VDD = 0V.

DS21877A-page 4

 2004 Microchip Technology Inc.

Share Link: