MAX6806/MAX6807/MAX6808
Voltage Detectors
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_______________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 micro-
processor (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 guaran-
teed 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 pull-up 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 100kΩ 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 sec-
tion).
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 80kΩ pull-down resistor, so the input may be left
unconnected if not used. Connect a normally open
momentary switch from MR to V
CC
to create a manual-
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 hys-
teresis 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 oscil-
lating (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.
