MAX44268 Maxim, MAX44268 Datasheet - Page 10

• Manufacturer Part Number: MAX44268
• Description: The MAX44268 is an ultra-small and low-power dual comparator ideal for battery-powered applications such as cell phones, notebooks, and portable medical devices that have extremely aggressive board space and power constraints
• Manufacturer: Maxim

Use the following procedure to calculate resistor values.
1) Select R3. Input bias current at IN_+ is less than
2) Choose the hysteresis band required (V
3) Calculate R2 according to the following equation:
For this example, insert the value:
For this example, choose standard value R2 = 9.76kI.
4) Choose the trip point for V
5) Calculate R4 as follows:
15nA. To minimize errors caused by the input bias
current, the current through R3 should be at least
1.5µA. Current through R3 at the trip point is (V
V
in solving for R3 yields two formulas:
Use the smaller of the two resulting resistor values.
For example, for V
200kI, and a V
are 827kI and 1.5MI. Therefore, for R3 choose the
standard value of 825kI.
example, the V
way that:
V
parator switches its output from low to high, as V
rises above the trip point. For this example, choose
V
=
R3 = V
OUT
THR
THR
R4
=
R2 (200k
)/R3. Considering the two possible output states
= 3V.
is the threshold voltage at which the com-
R2 (R1 R3)



=
REF
1.236V x 9.76
R4
/IR3 and R3 = [(V
=
V
3
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Ω +
HB
+
THR



REF
V
REF
= 50mV.
0.825M )
V
>
THR
= 1.236V, the two resistor values




CC
V
V
x R2
 
 

1
CC
REF
-

= 5V, IR3 = -1.5µA, R1 =
9.76
Ω
 
 

+



1
1
IN
-
1
(V




CC
+
V
50mV
R2
rising (V
 
 
 
REF
1
5.3
HB
V
V
-
HB
CC
 
 
 
- V
=
825
-
xR1) R3
=
1
REF






R3
1



THR
9.67k



Dual Comparator with Reference
)/IR3] - R1
6.93k
HB




) in such a
Ω
). In this
Ω
REF
1.3mm x 1.3mm, Low-Power
IN
-
For this example, choose a standard value of 6.98kI.
6) Verify the trip voltages and hysteresis as follows:
The hysteresis network in
reference voltage is chosen to be at midrail and the trip
points of the comparator are chosen to be symmetrical
about the reference voltage. Use the circuit in
if the reference voltage can be designed to be at the
center of the hysteresis band. For the symmetrical case,
follow the same steps outlined in the paragraph above
to calculate the resistor values except that in this case,
resistor R4 approaches infinity (open). So in the previ-
ous example, using comparator B with V
V
formulas, results in R1 = 200kI, R2 = 9.09kI, and R3 =
825kI, R4 = not installed.
Due to the open-drain output of the IC, the device can
translate between two different logic levels
the internal 4mV hysteresis is not sufficient, then external
resistors can be added to increase the hysteresis as
shown in
Figure 3. Simplified External Hysteresis Network if V
the Center of the Hysteresis Band
THR
V
=
= 2.525V and V
IN
V
=
THF
V
Figure 2
THR
R2
V
REF
V
V
REF
and
REF
x R2
-
THF
R1 R3
xR2
R3
Figure
R2



+



Figure 2
= 2.475V then using the above
R2
MAX44268



1



Logic-Level Translator
R2
V
1
 
 
 
x V
CC
3.
+
GND
 
 
 
MAX44268
+
CC
R1 R3
can be simplified if the
R3
+
1
1
 
 
 
OUT
+
 
 
 
+
R4
REF
1
(Figure
R4



1



REF
= 2.5V, if



Figure 3



R1
is at
4). If