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MAX9117 Datasheet, PDF (11/13 Pages) Maxim Integrated Products – SC70, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference
◁
SC70, 1.8V, Nanopower, Beyond-the-Rails
Comparators With/Without Reference
IN+
VTHR
IN-
VHB
VTHF
THRESHOLDS
HYSTERESIS
BAND
OUT
VCC
R3
R1
VIN
R2
VREF
VCC
OUT
VEE
MAX9117
MAX9119
Figure 2. Threshold Hysteresis Band
MAX9117 (VREF = 1.252V) and VCC = +5V, and if
we choose IR3 = 1µA, then the two resistor values
are 1.2MΩ and 3.8MΩ. Choose a 1.2MΩ standard
value for R3.
2) Choose the hysteresis band required (VHB). For this
example, choose 50mV.
3) Calculate R1 according to the following equation:
R1 = R3 (VHB / VCC)
For this example, insert the values:
R1 = 1.2MΩ (50mV / 5V) = 12kΩ
4) Choose the trip point for VIN rising (VTHR) such that
VTHR > VREF ✕ (R1 + R3) / R3, (VTHF is the trip point
for VIN falling). This is the threshold voltage at which
the comparator switches its output from low to high
as VIN rises above the trip point. For this example,
choose 3V.
5) Calculate R2 as follows:
R2 = 1 / [VTHR / (VREF ✕ R1) - (1 / R1) - (1 / R3)]
R2 = 1 / [3.0V / (1.2V ✕ 12kΩ) - (1 / 12kΩ) -
(1 / 1.2MΩ)] = 8.05kΩ
For this example, choose an 8.2kΩ standard value.
6) Verify the trip voltages and hysteresis as follows:
VIN rising: VTHR = VREF ✕ R1 [(1 / R1) + (1 / R2)
+ (1 / R3)]
VIN falling: VTHF = VTHR - (R1 ✕ VCC / R3)
Hysteresis = VTHR - VTHF
Additional Hysteresis (MAX9118/MAX9120)
The MAX9118/MAX9120 have a 4mV internal hysteresis
band. They have open-drain outputs and require an
Figure 3. MAX9117/MAX9119 Additional Hysteresis
external pullup resistor (Figure 4). Additional hysteresis
can be generated using positive feedback, but the for-
mulas differ slightly from those of the MAX9117/
MAX9119. Use the following procedure to calculate
resistor values.
1) Select R3 according to the formulas R3 = VREF / 1µA
or R3 = (VCC - VREF) / 1µA - R4. Use the smaller of
the two resulting resistor values.
2) Choose the hysteresis band required (VHB).
3) Calculate R1 according to the following equation:
R1 = (R3 + R4) (VHB / VCC)
4) Choose the trip point for VIN rising (VTHR) (VTHF is
the trip point for VIN falling). This is the threshold
voltage at which the comparator switches its output
from low to high as VIN rises above the trip point.
5) Calculate R2 as follows:

R2 = 1 VTHR (VREF
×

R1) − 
1


 R1
−
1


R3 
6) Verify the trip voltages and hysteresis as follows:
VIN rising:
VTHR = VREF
×

R1 
1
+
1
+
1

 R1 R2 R3
VIN falling:
VTHF
=
VREF
×
R1


1
R1
+
1
R2
+
R3
1
+ R4 
−
R3
R1
+
R4
×
VCC
Hysteresis = VTHR - VTHF
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