MAX9017BEKA(2003) View Datasheet(PDF) - Maxim Integrated
Part Name
Description
MFG CO.
MAX9017BEKA
(Rev.:2003)
(Rev.:2003)
Maxim Integrated
MAX9017BEKA Datasheet PDF : 16 Pages
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SOT23, Dual, Precision, 1.8V, Nanopower
Comparators With/Without Reference
Internal Hysteresis
Many comparators oscillate in the linear region of oper-
ation because of noise or undesired parasitic feed-
back. Oscillations can occur when the voltage on one
input is equal or very close to the voltage on the other
input. The MAX9015–MAX9020 have internal 4mV hys-
teresis to counter parasitic effects and noise.
The hysteresis in a comparator creates two trip points:
one for the rising input voltage (VTHR) and one for the
falling input voltage (VTHF) (Figure 1). The difference
between the trip points is the hysteresis (VHB). When
the comparator’s input voltages are equal, the hystere-
sis effectively causes one comparator input to move
quickly past the other, thus taking the input out of the
region where oscillation occurs. Figure 1 illustrates the
case in which the comparator’s inverting input has a
fixed voltage applied, and the noninverting input is var-
ied. If the inputs were reversed, the figure would be the
same, except with an inverted output.
Additional Hysteresis
(MAX9015/MAX9017/MAX9019)
(Push-Pull Outputs)
The MAX9015/MAX9017/MAX9019 feature a built-in
4mV hysteresis band (VHB). Additional hysteresis can
be generated with three resistors using positive feed-
back (Figure 2). Use the following procedure to calcu-
late resistor values:
1) Select R3. Input bias current at IN_+ is less than
2nA, so the current through R3 should be at least
0.2µA to minimize errors caused by input bias cur-
rent. The current through R3 at the trip point is
(VREF - VOUT)/R3. Considering the two possible out-
put states in solving for R3 yields two formulas: R3
= VREF/IR3 or R3 = (VCC - VREF)/IR3. Use the small-
er of the two resulting resistor values. For example,
when using the MAX9017 (VREF = 1.24V) and VCC
= 5V, and if we choose IR3 = 0.2µA, then the two
resistor values are 6.2MΩ and 19MΩ. Choose a
6.2MΩ 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 VVHCBC
For this example, insert the values:
R1 =
6.2MΩ
50mV
5V
=
12kΩ
IN+
VTHR
IN-
VHB
VTHF
THRESHOLDS
HYSTERESIS
BAND
OUT
Figure 1. Threshold Hysteresis Band
VCC
R3
R1
VIN
R2
VREF
VCC
OUT
VEE
MAX9015
MAX9017
MAX9019
Figure 2. MAX9015/MAX9017/MAX9019 Additional Hysteresis
4) Choose the trip point for VIN rising (VTHR) such that:
VTHR
>
VREF
1 +
VHB
VCC
where VTHR is the trip point for VIN rising. 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 X
R1
−
1
R1
−
1
R3
R2 =
1
= 43.99kΩ
(1.24
3.0V
V X 62kΩ)
−
1
62kΩ
−
1
6.2MΩ
For this example, choose a 44.2kΩ standard value.
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