SP691ACN SIPEX [Sipex Corporation], SP691ACN Datasheet - Page 18

• Manufacturer Part Number: SP691ACN
• Description: Low Power Microprocessor Supervisory with Battery Switch-Over
• Manufacturer: SIPEX [Sipex Corporation]

Figure 28. Monitoring a Negative Voltage
Negative-Going V
While asserting resets to the µP during power-up,
power-down, and brownout conditions, these
supervisors are relatively immune to short-
duration negative-going V
usually undesirable to reset the µP when V
experiences only small glitches.
Refer to Figure 29 for a graph of the maximum
transient duration vs. the reset-comparator over-
drive for which reset pulses are not generated.
The graph was produced using negative-going
pulses, starting at 5V and ending below the
reset threshold by the magnitude indicated
(reset comparator overdrive). The graph shows
the maximum pulse width a negative-going V
transient may typically have without causing a
reset pulse to be issued.
Date: 5/25/04
+5V
GND
V
*V
*V
CC
5.0 - 1.25
SP691A/693A/800L/800M Low Power Microprocessor Supervisor with Battery Switch-Over © Copyright 2004 Sipex Corporation
TRIP
TRIP
R
PFO
PFI
PFO
1
is a negative voltage
0V
CC
+5V
0V
Transients
=
CC
1.25 - V
transients. It is
R
V-
2
V-
TRIP
R
R
2
1
CC
CC
18
Figure 29. Maximum Transient Duration Without
Causing a Reset Pulse vs. Reset Comparator Overdrive
As the amplitude of the transient increases
(i.e., goes farther below the reset threshold), the
maximum allowable pulse width decreases.
Typically, a V
below the reset threshold and lasts for 40µs or
less will not cause a reset pulse to be issued.
A 100nF bypass capacitor mounted close to the
V
Connecting a Timing Capacitor to OSC
When OSC
disconnects from its internal 10µA pull-up and
is internally connected to a +100nA current
source. When a capacitor is connected from
OSC
watchdog timeout period), the current source
charges and discharges the timing capacitor to
create the oscillator that controls the reset and
watchdog timeout period. To prevent timing
errors, minimize external current leakage
sources at this pin, and locate the capacitor as
close to OSC
board leakage plus the OSC capacitor leakage
must be small compared to +100nA.
CC
160
120
pin provides additional transient immunity.
80
40
IN
0
1
to ground (to select an alternative
(Reset Threshold Voltage - V
SEL
IN
Reset Comparator Overdrive
CC
is connected to ground, OSC
as possible. The sum of any PC
transient that goes 100mV
10
0.1µF Capacitor
V
Reset Generated
OUT
Above Line
1000
to GND
CC
), (mV)
10000
IN
IN