Datasheet

Applications Information
Negative-Going V
CC
Transients
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-com-
parator 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 ending
below it by the magnitude indicated (reset-comparator
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
provides additional
transient immunity.
Ensuring a Valid 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
applications, since most circuitry is inoperative when
V
CC
is below 1V. In applications where RESET must
be valid down to ground, add a pulldown 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, 100kW will not
load RESET and will pull RESET to ground. Similarly,
if RESET (MAX6807) must be valid below 1.2V, add a
pullup resistor to RESET.
Figure 4. RESET / RESET Valid to V
CC
= Ground CircuitFigure 3. Maximum Transient Duration without Causing a Reset
Pulse vs. Reset Comparator Overdrive
MAX6806 MAX6807
V
CC
V
CC
GND
GND
RESET
RESET
R1
100kΩ
R1
100kΩ
80
70
20
10 100 1000
40
30
50
60
RESET COMPARATOR OVERDRIVE, V
TH-
- V
CC
(mV)
MAXIMUM TRANSIENT DURATION (µs)
T
A
= +25°C
MAX680 46
www.maximintegrated.com
Maxim Integrated │ 5
MAX6806/MAX6807/
MAX6808
Voltage Detectors