Datasheet

MAX9015–MAX9020
SOT23, Dual, Precision, 1.8V, Nanopower
Comparators With/Without Reference
12
Maxim Integrated
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 (V
THR
) and one for the
falling input voltage (V
THF
) (Figure 1). The difference
between the trip points is the hysteresis (V
HB
). 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 (V
HB
). 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
(V
REF
- V
OUT
)/R3. Considering the two possible out-
put states in solving for R3 yields two formulas: R3
= V
REF
/IR3 or R3 = (V
CC
- V
REF
)/I
R3
. Use the small-
er of the two resulting resistor values. For example,
when using the MAX9017 (V
REF
= 1.24V) and V
CC
= 5V, and if we choose I
R3
= 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 (V
HB
). For this
example, choose 50mV.
3) Calculate R1 according to the following equation:
For this example, insert the values:
4) Choose the trip point for V
IN
rising (V
THR
) such that:
where V
THR
is the trip point for V
IN
rising. This is the
threshold voltage at which the comparator switches
its output from low to high as V
IN
rises above the
trip point. For this example, choose 3V.
5) Calculate R2 as follows:
For this example, choose a 44.2kΩ standard value.
R
VX k k M
k
V
2
1
124 62
1
62
1
62
43 99
30
=
Ω
⎛
⎝
⎜
⎞
⎠
⎟
−
Ω
⎛
⎝
⎜
⎞
⎠
⎟
−
Ω
⎛
⎝
⎜
⎞
⎠
⎟
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
=Ω
(. ) .
.
.
R
V
VXRRR
THR
REF
2
1
1
1
1
1
3
=
⎛
⎝
⎜
⎞
⎠
⎟
−
⎛
⎝
⎜
⎞
⎠
⎟
−
⎛
⎝
⎜
⎞
⎠
⎟
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
VV
V
V
THR REF
HB
CC
>+
⎛
⎝
⎜
⎞
⎠
⎟
1
RM
mV
V
k162
50
5
12=Ω
⎛
⎝
⎜
⎞
⎠
⎟
=Ω.
RR
V
V
HB
CC
13=
⎛
⎝
⎜
⎞
⎠
⎟
THRESHOLDS
OUT
IN+
IN-
V
HB
HYSTERESIS
BAND
V
THF
V
THR
Figure 1. Threshold Hysteresis Band
V
CC
MAX9015
MAX9017
MAX9019
OUT
R3
R1
R2
V
REF
V
EE
V
IN
V
CC
Figure 2. MAX9015/MAX9017/MAX9019 Additional Hysteresis