Datasheet

MAX9015–MAX9020
SOT23, Dual, Precision, 1.8V, Nanopower
Comparators With/Without Reference
13
Maxim Integrated
6) Verify the trip voltages and hysteresis as follows:
V
IN
rising: = 2.992V, which is equivalent to REF
times R1 divided by the parallel combination of R1,
R2:
and R3.
V
IN
falling: = 2.942V:
Hysteresis = V
THR
- V
THF
= 50mV.
Additional Hysteresis
(MAX9016/MAX9018/MAX9020)
(Open-Drain Outputs)
The MAX9016/MAX9018/MAX9020 feature a built-in 4mV
hysteresis band. These devices have open-drain outputs
and require an external pullup resistor (Figure 3).
Additional hysteresis can be generated using positive
feedback, but the formulas differ slightly from those of
the MAX9015/MAX9017/MAX9019. Use the following
procedure to calculate 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
/I
R3
or R3 = [(V
CC
- V
REF
)/I
R3
] - R4. Use the
smaller of the two resulting resistor values. For
example, when using the MAX9018 (V
REF
= 1.24V)
and V
CC
= 5V, and if we choose I
R3
= 0.2µA, and
R4 = 1MΩ, then the two resistor values are 6.2MΩ
and 18MΩ. Choose a 6.2MΩ standard value for R3.
2) Choose the hysteresis band required (V
HB
).
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:
(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 49.9kΩ standard value.
6) Verify the trip voltages and hysteresis as follows:
Hysteresis = V
THR
- V
THF
= 50mV.
V falling V V x R
RR R
R
RR
xV V
IN THF REF
CC
:
.
=
⎛
⎝
⎜
⎞
⎠
⎟
+
⎛
⎝
⎜
⎞
⎠
⎟
+
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝
⎜
⎞
⎠
⎟
−
+
=
1
1
1
1
2
1
3
1
34
2 993
VrigV V xR
RR R
V
IN
THR
REF
sin :
.
=
⎛
⎝
⎜
⎞
⎠
⎟
+
⎛
⎝
⎜
⎞
⎠
⎟
+
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝
⎜
⎞
⎠
⎟
=
1
1
1
1
2
1
3
3 043
R
V
Vx k k M
k2
1
30
124 72
1
72
1
62
51 1=
Ω
⎛
⎝
⎜
⎞
⎠
⎟
−
Ω
⎛
⎝
⎜
⎞
⎠
⎟
−
Ω
⎛
⎝
⎜
⎞
⎠
⎟
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
=Ω
.
..
.
R
V
VxR R R
THR
REF
2
1
1
1
1
1
3
=
⎛
⎝
⎜
⎞
⎠
⎟
−
⎛
⎝
⎜
⎞
⎠
⎟
−
⎛
⎝
⎜
⎞
⎠
⎟
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
VV
V
V
THR REF
HB
CC
>+
⎛
⎝
⎜
⎞
⎠
⎟
1
RMM
mV
V
k162 1
50
5
72=Ω+Ω
⎛
⎝
⎜
⎞
⎠
⎟
=Ω(. )
RRR
V
V
HB
CC
134=+
⎛
⎝
⎜
⎞
⎠
⎟
()
VV
RxV
R
THF THR
CC
=−
⎛
⎝
⎜
⎞
⎠
⎟
1
3
VVxR
RR R
THR REF
=
⎛
⎝
⎜
⎞
⎠
⎟
+
⎛
⎝
⎜
⎞
⎠
⎟
+
⎛
⎝
⎜
⎞
⎠
⎟
⎡
⎣
⎢
⎤
⎦
⎥
1
1
1
1
2
1
3
V
EE
V
CC
OUT
R3
R2
R1
R4
V
REF
V
IN
V
CC
MAX9016
MAX9018
MAX9020
Figure 3. MAX9016/MAX9018/MAX9020 Additional Hysteresis