MAX932 Maxim, MAX932 Datasheet - Page 12

• Manufacturer Part Number: MAX932
• Description: The MAX931–MAX934 single, dual, and quad micropower, low-voltage comparators plus an on-board 2% accurate reference feature the lowest power consumption available
• Manufacturer: Maxim

Ultra Low-Power, Low-Cost
Comparators with 2% Reference
3. Calculate R2 + R3. The overvoltage threshold
4. Calculate R2. The undervoltage threshold should
5. Calculate R3.
6. Verify the resistor values. The equations are as
The high output source capability of the MAX931 series
is useful for driving LEDs. An example of this is the
simple four-stage level detector shown in Figure 7.
12
R2
100nA for the thresholds to be accurate. R1 values
up to about 10MΩ can be used, but values in the
100kΩ to 1MΩ range are usually easier to deal with.
In this example, choose R1 = 294kΩ.
should be 5.5V when V
equation is as follows:
be 4.5V when V
as follows:
Choose R3
follows, evaluated for the above example.
Overvoltage threshold :
Undervoltage threshold :
R2
Choose R2
where the hysteresis voltage V
______________________________________________________________________________________
R3
(R1 + R2 + R3)
(294k + 1.068M)
62.2k
V
V
OTH
UTH
R3
R1
294k
1.068M
61.9k (1% standard value).
1
(R2 + R3)
1.006M
1M (1% standard value).
(V
(V
5.474V.
4.484V,
IN
.068M
REF
REF
is falling. The design equation is
V
REF
(1.182
Bar-Graph Level Gauge
V
OTH
V )
V )
H
IN
H
6
(V
1 9 .
(1.182
REF
is rising. The design
R2
V
5.5
H
k
H
V
UTH
(R1
(R1
0.005)
4.5
(R1 + R2)
V
1
V )
REF
H
0.005)
R2
R2
R1
1
R1
R4
R5
R3)
R3)
294k
.
The full-scale threshold (all LEDs on) is given by
V
3/4 full scale, 1/2 full scale, and 1/4 full scale. The
output resistors limit the current into the LEDs.
Figure 8 shows a circuit to shift from bipolar ±5V inputs
to TTL signals. The 10kΩ resistors protect the
comparator inputs, and do not materially affect the
operation of the circuit.
Figure 9 shows the MAX932 monitoring an input
voltage in two steps. When V
LOW and FAIL thresholds, outputs are high. Threshold
calculations are similar to those for the window-
detector application.
Figure 7. Bar-Graph Level Gauge
IN
= (R1 + R2)/R1 volts. The other thresholds are at
250k
182k
250k
250k
250k
750mV
500mV
250mV
1.182V
R1
Two-Stage Low-Voltage Detector
1V
10
11
13
12
8
5
6
4
7
INA+
INB+
INC+
INC-
IND+
IND-
INB-
REF
INA-
MAX934
14
GND
+5V
V+
3
OUTB
OUTC
OUTD
OUTA
IN
V-
is higher than the
16
15
2
1
9
330
330
330
330
R2
Level Shifter
V
IN