MAX924 Maxim, MAX924 Datasheet - Page 12

• Manufacturer Part Number: MAX924
• Description: The MAX921–MAX924 single, dual, and quad micropower, low-voltage comparators feature the lowest power consumption available
• Manufacturer: Maxim

Ultra Low-Power,
Single/Dual-Supply Comparators
6. Verify the resistor values. The equations are as
12
2. Select R1. The leakage current into INB- is normally
3. Calculate R2 + R3. The overvoltage threshold
4. Calculate R2. The undervoltage threshold should
5. Calculate R3.
under 1nA, so the current through R1 should
exceed 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 = 1MΩ (1% standard value)
follows, evaluated for the above example.
R2
R3
Overvoltage threshold :
V
Undervoltage threshold :
V
where the hysteresis voltage V
R2
Choose R2
OTH
UTH
______________________________________________________________________________________
+
=
=
=
=
=
=
=
=
=
R3
(R1 + R2 + R3)
(294k + 1.068M)
62.2k
=
1
(R2 + R3)
1.006M
.068M
4.484V,
(V
(V
5.474V.
REF
REF
=
=
=
Ω
=
R1
294k
1.068M
61.9k (1% standard value).
Ω
−
+
−
IN
V )
V )
×
H
H
6
−
Ω
is falling. The design equation is
×
1 9 .
⎛
⎜
⎝
Ω
R2
×
×
V
⎛
⎜
⎝
REF
k
×
×
(1.182
(R1
(R1
V
OTH
(V
(1.182
IN
(R1 + R2)
H
+
REF
+
+
V
is rising. The design
V
5.5
UTH
=
R2
R2
R1
H
+
−
4.5
V
−
0.005)
REF
+
V )
+
−
0.005)
H
R3)
R3)
1
×
⎞
⎟
⎠
−
R5
R4
R1
−
−
.
294k
1
⎞
⎟
⎠
The high output source capability of the MAX921 series
is useful for driving LEDs. An example of this is the
simple four-stage level detector shown in Figure 7.
The full-scale threshold (all LEDs on) is given by V
(R1 + R2)/R1 volts. The other thresholds are at 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 6. Window Detector
R3
R2
V
IN
R1
V
V
10k
R5
2.4M
R4
OTH
UTH
= 5.5V
= 4.5V
HYST
REF
INB-
INA+
V-
MAX923
Bar-Graph Level Gauge
+5V
V+
OUTA
OUTB
Level Shifter
UNDERVOLTAGE
OVERVOLTAGE
POWER GOOD
IN
=