_______________Detailed Description
The MAX836/MAX837 micropower voltage monitors
contain a 1.204V precision bandgap reference and a
comparator (see the
Typical Operating Circuit
). The
only difference between the two parts is the structure of
the comparator output driver. The MAX836 has an
open-drain N-channel output driver that can be pulled
up to a voltage higher than V
CC
, but under 11V. The
MAX837’s output is push-pull, and can both source
and sink current.
Programming the Trip Voltage
Two external resistors set the trip voltage, V
TRIP
(Figure 1).
V
TRIP
is the point at which the applied voltage (typically
V
CC
) toggles OUT. The MAX836/MAX837’s high input
impedance allows large-value resistors without compro-
mising trip-voltage accuracy. To minimize current con-
sumption, select a value for R2 between 500kΩ and
1MΩ, then calculate R1 as follows:
where V
TRIP
= desired trip voltage (in volts), V
TH
=
threshold trip voltage (1.204V).
__________Applications Information
Adding Hysteresis
Hysteresis adds noise immunity to the MAX836/MAX837
and prevents repeated triggering when V
IN
is near the
threshold trip voltage. Figure 2 shows how to add hys-
teresis to the comparator. The technique is similar for
R1 = R2
V
V
-1
TRIP
TH
MAX836/MAX837
4-Pin Micropower Voltage Monitors
4 _______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(V
CC
= +5V, R
LOAD
= 1MΩ, R
PULL-UP
= 10kΩ (MAX836 only), T
A
= +25°C, unless otherwise noted.)
_____________________Pin Description
NAME FUNCTION
1
GND System Ground
2 V
CC
System Supply Input
PIN
3 IN
Noninverting Input to the Comparator.
The inverting input connects to the
internal 1.204V bandgap reference.
4 OUT
Open-Drain (MAX836) or
Push-Pull (MAX837) Output
GND
R
PULL-UP
OUT
IN
MAX836
V
CC
V
CC
V
CC
R2
R1
R1 + R2
R2
V
TRIP
= (1.204)
NOTE: UNITS ARE OHMS AND VOLTS
0.1µF
Figure 1. Programming the Trip Voltage, V
TRIP
0
200
400
600
800
1000
1200
1400
1600
1800
24 8
OUT RISE/FALL TIME vs.
SUPPLY VOLTAGE
MAX836/7 10
V
CC
(V)
TIME (ns)
61035 971112
FALL TIME
RISE TIME
MAX837 ONLY
40
160
140
120
100
80
60
-60 -20 60
V
CC
FALLING PROPAGATION DELAY
vs. TEMPERATURE
MAX836/7 09
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
20-40 0 8040 100
1mV/µs
10mV/µs
V
TRIP
= 3.0V
V
TRIP
= 3.0V
V
TRIP
= 4.63V
V
TRIP
= 4.63V
(16 Seiten)
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