Datasheet

Detailed Description
Reset Output
The MAX6806 voltage detector features an active-low,
push-pull RESET output, while the MAX6807 features an
active-high, push-pull RESET output. Unlike micropro-
cessor (µP) supervisory circuits that offer a reset timeout
period, the MAX6806 and MAX6807 RESET goes high
and RESET goes low virtually immediately once V
CC
exceeds the reset threshold. If a brownout occurs (V
CC
falls below the reset threshold), RESET goes low and
RESET goes high. RESET is guaranteed to be a logic
low for V
CC
≥ 1V and RESET is guaranteed to be a logic
high for V
CC
≥ 1.2V.
The MAX6808 features an active-low, open-drain RESET
output. The output sinks current when V
CC
falls below
the reset threshold. Connect a pullup resistor from
RESET to any supply voltage up to 6V (Figure 1). Select
a resistor value large enough to provide a logic low and
small enough to provide a logic high while supplying all
input and leakage currents connected to the RESET
line. A 100kW resistor is sufficient in applications driving
high-impedance loads.
The manual reset input (MR, 4-pin SOT143 package) can
also initiate a reset (see Manual Reset Input section).
Manual-Reset Input
Many applications require manual-reset capabilities,
allowing an operator, a test technician, or external logic
circuitry to initiate a reset. A logic high on MR asserts
a reset and remains asserted while MR is high. This
input has an 80kW pulldown resistor, so the input can be
left unconnected if not used. Connect a normally open
momentary switch from MR to V
CC
to create a manu-
al-reset function. If MR is driven from long cables or if the
device is used in a noisy environment, connecting a 0.1µF
capacitor from MR to ground provides noise immunity.
Hysteresis
The MAX6806/MAX6807/MAX6808 feature internal
hysteresis that creates two trip points: one for the rising
supply voltage and one for the falling supply voltage
(Figure 2). The hysteresis prevents the output from
oscillating (chattering) when V
CC
is near the reset
threshold.
Reset Threshold Accuracy
The MAX6806/MAX6807/MAX6808 are ideal for
sys-tems using a 5V ±5%, 3V ±5%, or 2.5V ±5% power
supply with ICs specified for 5V ±10%, 3V ±10%, or
2.5V ±10%, respectively. The reset is guaranteed to
assert after the power supply falls out of regulation,
but before power drops below the minimum specified
oper-ating voltage range for the system ICs.
Figure 2. Input and Output Waveforms with V
CC
VariedFigure 1. The MAX6808 Open-Drain RESET Output Allows Use
with Multiple Supplies
V
TH+
HYST
RESET
(MAX6806/MAX6808)
RESET
(MAX6807)
V
HYST
= V
TH+
- V
TH-
V
OH
V
OL
V
OH
V
OL
V
TH-
MAX6808
V
CC
V
CC
GND
+3.3V
GND
+5.0V
100kΩ
5V SYSTEM
RESET
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MAX6806/MAX6807/
MAX6808
Voltage Detectors