TCM812TERCTR View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TCM812TERCTR Datasheet PDF : 16 Pages
| |||
4.0 APPLICATIONS INFORMATION
The TCM811/TCM812 provides accurate VDD
monitoring and reset timing during power-up, power-
down, and brownout/sag conditions. These devices
also reject negative-going transients (glitches) on the
power supply line. Figure 4-1 shows the maximum
transient duration vs. maximum negative excursion
(overdrive) for glitch rejection. Any combination of
duration and overdrive 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 proximity to the VDD pin of the TCM811/
TCM812.
VDD
VTH
Overdrive = VD D
Duration
400
TA = +25˚C
320
240
160
TCM81xL/M
80
TCM81xR/S/T
0
1
10
100
1000
RESET COMPARATOR OVERDRIVE,
VTH - VDD (mV)
FIGURE 4-1: Maximum Transient Duration
vs. Overdrive for Glitch Rejection at +25°C.
4.1 RESET Signal Integrity During
Power-Down
The TCM811 RESET push-pull output is valid to
VDD = 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
completely shutdown well above this voltage. How-
ever, in situations where RESET must be maintained
valid to VDD = 0V, a pull-down resistor must be con-
nected from RESET to ground to discharge stray
capacitances and hold the output low (Figure 4-2). This
resistor value, though not critical, should be chosen
© 2007 Microchip Technology Inc.
TCM811/TCM812
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 TCM812 to ensure a valid high RESET
for VDD below 1.1V.
VDD
0.1µF
4
VDD
TCM811
2
RESET
GND
1
R1
100 kΩ
FIGURE 4-2:
The addition of R1 at the
RESET output of the TCM811 ensures that the
RESET output is valid to VDD = 0V.
4.2 Controllers and Processors With
Bidirectional I/O Pins
Some microcontrollers have bidirectional reset pins.
Depending on the current drive capability of the
controller pin, an indeterminate logic level may result if
there is a logic conflict. This can be avoided by adding
a 4.7 kΩ resistor in series with the output of the
TCM811/TCM812 (Figure 4-3). 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.
Buffered RESET
To Other System
Components
BUFFER
VDD
0.1µF
4
TCM811
4.7 kΩ
RESET
2
Micro
controller
RESET
GND
1
GND
FIGURE 4-3:
Interfacing the TCM811 to a
Bidirectional Reset I/O.
DS21615C-page 7
Share Link: 