TCM811 Microchip Technology, TCM811 Datasheet - Page 4

• Manufacturer Part Number: TCM811
• Description: 4-Pin Microcontroller Reset Monitors
• Manufacturer: Microchip Technology

TCM811/TCM812
2.0
The TCM811/TCM812 provides accurate V
ing and reset timing during power-up, power-down, and
brownout/sag conditions. These devices also reject
negative-going transients (glitches) on the power sup-
ply line. Figure 2-1 shows the maximum transient dura-
tion vs. maximum negative excursion (overdrive) for
glitch rejection. Any combination of duration and over-
drive that is under the curve will not generate a reset
signal. Combinations above the curve are detected as
a brownout or power-down. Transient immunity can be
improved by adding a 0.1 µF capacitor in close proxim-
ity to the V
FIGURE 2-1:
Overdrive for Glitch Rejection at 25°C.
2.1
The TCM811 RESET push-pull output is valid to V
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 com-
pletely shutdown well above this voltage. However, in
situations where RESET must be maintained valid to
V
RESET to ground to discharge stray capacitances and
hold the output low (Figure 2-2). This resistor value,
though not critical, should be chosen such that it does
not appreciably load RESET under normal operation
DS21615B-page 4
DD
= 0V, a pull-down resistor must be connected from
400
320
240
160
APPLICATIONS INFORMATION
80
RESET Signal Integrity During Power-
Down
0
DD
V
1
DD
RESET COMPARATOR OVERDRIVE,
pin of the TCM811/812.
T
TCM81xR/S/T
A
= +25˚C
Maximum
V TH - V DD (mV)
10
TCM81xL/M
Duration
Transient
100
Overdrive =
V
TH
Duration
V
1000
DD
D D
monitor-
DD
vs.
=
(100 k
larly, a pull-up resistor to V
TCM812 to ensure a valid high RESET for V
1.1V.
FIGURE 2-2:
output of the TCM811 ensures that the RESET output
is valid to V
2.2
Some microcontrollers have bi-directional reset pins.
Depending on the current drive capability of the control-
ler 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 TCM811/
TCM812 (Figure 2-3). If there are other components in
the system which 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 2-3:
directional Reset I/O.
0.1µF
0.1µF
will be suitable for most applications). Simi-
Controllers and Processors With
Bidirectional I/O Pins
V
DD
DD
= 0V.
TCM811
The addition of R
Interfacing the TCM811 to a Bi-
GND
RESET
1
4
TCM811
GND
V
V
DD
2
RESET
DD
2002 Microchip Technology Inc.
4.7 k
4
1
BUFFER
DD
is required for the
2
RESET
1
controller
Buffered RESET
To Other System
Components
at the RESET
Micro
GND
R
100 k
1
DD
below