TCM810R View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

TCM810R

3-Pin Microcontroller Reset Monitors

Microchip Technology 

3.0 APPLICATIONS INFORMATION

3.1 VDD Transient Rejection

The TCM809/TCM810 provides accurate VDD monitor-

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

brown-out/sag conditions. These devices also reject

negative-going transients (glitches) on the power sup-

ply line. Figure 3-1 shows the maximum transient dura-

tion vs. maximum negative excursion (overdrive) for

glitch rejection. Any combination of duration and over-

drive that lies under the curve will not generate a reset

signal.

VDD

VTH

Overdrive

Duration

400

TA = +25°C

320

240

160

TCM8XXL/M/J (SOT-23)

80

TCM8XXZ/R/S/T

0 (SOT-23)

1

5

100

1000

Reset Comparator Overdrive

[VTH - VDD] (mv)

130

120

110

100

90

80

70

60

50

40

30

1

TCM8XXL/M/J (SC-70)

TCM8XXZ/R/S/T (SC-70)

10

100

Reset Comparator Overdrive (mV)

[VTH - VDD] (mv)

1000

FIGURE 3-1:

Maximum Transient

Duration vs. Overdrive for Glitch Rejection at

+25°C.

TCM809/TCM810

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 TCM809/TCM810.

3.2 RESET Signal Integrity During

Power-Down

The TCM809 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

completely shut down well above this voltage.

However, in situations where RESET must be main-

tained 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). Similarly, a pull-up resistor to VDD is

required for the TCM810 to ensure a valid high RESET

for VDD below 1.0V.

VDD

VDD

TCM809

RESET

GND

R1

100 kΩ

FIGURE 3-2:

The addition of R1 at the

RESET output of the TCM809 ensures that the

RESET output is valid to VDD = 0V.

 2004 Microchip Technology Inc.

DS21661C-page 5

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