
Applic ations Information
Negative-Going V
CC
T ransients
In addition to asserting a reset signal during power-up,
power-down, and brown-out conditions, the MAX6806/
MAX6807/MAX6808 are immune to short-duration, neg-
ative-going V
CC
transients.
Figure 3 displays typical transient durations vs. reset-
comparator overdrive for which the MAX6806/MAX6807/
MAX6808 do
not
generate a reset pulse. The graph was
generated using a negative-going pulse applied to V
CC
,
starting 0.5V above the actual reset threshold and end-
ing below it by the magnitude indicated (reset-compara-
tor overdrive). The graph indicates the maximum pulse
width a negative-going V
CC
transient can have without
causing a reset pulse. As the magnitude of the transient
increases (goes further below the reset threshold), the
maximum allowable pulse width decreases. A 0.1μF
capacitor mounted as close as possible to V
CC
pro-
vides additional transient immunity.
Ensuring a V alid Reset Output Down to
V
CC
= Ground
When V
CC
falls below 1V, the MAX6806/MAX6808
RESET
output no longer sinks current—it becomes an
open circuit. Therefore, high-impedance CMOS logic
inputs connected to
RESET
can drift to undetermined
voltages. This presents no problem in most applica-
tions, since most circuitry is inoperative when V
CC
is
below 1V. In applications where
RESET
must be valid
down to ground, add a pull-down resistor to
RESET
so
any stray leakage currents flow to ground, holding
RESET
low (Figure 4). Select R1 to be large enough not
to load
RESET
and small enough to pull
RESET
to
ground. For most applications, 100k
will not load
RESET
and will pull
RESET
to ground. Similarly, if
RESET (MAX6807) must be valid below 1.2V, add a
pull-up resistor to RESET.
M
Voltage Detec tors
_______________________________________________________________________________________
5
80
70
20
10
RESET COMPARATOR OVERDRIVE, V
TH-
- V
CC
(mV)
100
1000
40
30
50
60
M
μ
s
T
A
= +25°C
MAX680 46
Figure 3. Maximum Transient Duration without Causing a
Reset Pulse vs. Reset Comparator Overdrive
MAX6806
MAX6807
V
CC
V
CC
GND
GND
RESET
RESET
R1
100k
R1
100k
Figure 4.
RESET
/ RESET Valid to V
CC
= Ground Circuit