Datasheet

MCP120/130
DS11184D-page 4  2001 Microchip Technology Inc.
2.0 APPLICATIONS INFORMATION
2.1 The Need for Supervisory Circuits
For many of today’s microcontroller applications, care
must be taken to prevent low power conditions that can
cause many different system problems. The most com-
mon causes are brown-out conditions where the sys-
tem supply drops below the operating level momentar-
ily, and the second, is when a slowly decaying power
supply causes the microcontroller to begin executing
instructions without enough voltage to sustain SRAM
and producing indeterminate results.
Figure 2-1: Typical Application
2.2 Negative Going VDD Transients
Many system designers implementing POR circuits are
concerned about the minimum pulse width required to
cause a reset. Figure 2-2 shows typical transient
voltage below the trip point (V
TRIP - VDD) vs. transient
duration. It shows that the farther below the trip point
the transient pulse goes, the duration of the pulse
required to cause a reset gets shorter. A 0.1 µF bypass
cap mounted as close as possible to the VDD pin pro-
vides additional transient immunity.
Figure 2-2: Typical Transient Response
Microcontroller
MCLR
VSS
RST
MCP120
or
RESET
VSS
VDD
VDD
Bypass
Capacitor
VDD
TIME
SUPPLY VOLTAGE
0
0
5V
VTRIP
MAX
VTRIP
MIN
Transient
Duration
(VTRIP
MIN -
VDD)
0123
V
TRIP - VDD (V)
10
8
6
4
2
0
TRANSIENT DURATION (
µ
S)
45
TA = +25°C
Transients above the
curve will cause a reset
Transients below
the curve will NOT
cause a reset