MAX9017 Maxim, MAX9017 Datasheet - Page 14

• Manufacturer Part Number: MAX9017
• Description: The single MAX9015/MAX9016 and dual MAX9017–MAX9020 nanopower comparators in space-saving SOT23 packages feature Beyond-the-Rails™ inputs and are guaranteed to operate down to 1
• Manufacturer: Maxim

The MAX9015–MAX9020 ultra-low supply current typi-
cally requires no power-supply bypass capacitors.
However, when the supply has high output impedance,
long lead lengths or excessive noise, or fast transients,
bypass V
close to the V
lengths to reduce stray capacitance. Use a ground
plane and surface-mount components for best perfor-
mance. If REF is decoupled, use a low-leakage ceram-
ic capacitor.
The MAX9018 is ideal for window detectors (undervolt-
age/overvoltage detectors). Figure 4 shows a window
detector circuit for a single-cell Li+ battery with a 2.9V
end-of-life charge, a peak charge of 4.2V, and a nomi-
nal value of 3.6V. Choose different thresholds by
changing the values of R1, R2, and R3. OUTA provides
an active-low undervoltage indication, and OUTB pro-
vides an active-low overvoltage indication. ANDing the
two open-drain outputs provides an active-high, power-
good signal.
The design procedure is as follows:
1) Select R1. The input bias current into INB- is nor-
2) Calculate R2 + R3. The overvoltage threshold
3) Calculate R2. The undervoltage threshold should
SOT23, Dual, Precision, 1.8V, Nanopower
Comparators With/Without Reference
14
mally less than 2nA, so the current through R1
should exceed 100nA for the thresholds to be accu-
rate. In this example, choose R1 = 1.24MΩ
(1.24V/1µA).
should be 4.2V when V
equation is as follows:
be 2.9V when V
as follows:
______________________________________________________________________________________
R
2
R
CC
= 546kΩ
=
=
2
(
( .
+
R
1 24
to V
CC
1
R
+
3
M
pin as possible. Minimize signal trace
EE
=2.95MΩ
R
=
=
Board Layout and Bypassing
Ω +
2
IN
1 24
R x
with a 0.1µF capacitor placed as
+
1
.
is falling. The design equation is
R
2 95
M
3
.
⎡
⎢
⎢
⎣
)
⎛
⎜
⎝
Ω
x
V
M
x
REF
IN
⎛
⎜
⎝
Ω
V
V
⎡
⎢
⎢
⎣
)
⎛
⎜
⎝
REF
is rising. The design
OTH
Window Detector
1 24
x
+
.
V
( .
V
UTH
1 236
HB
−
2 9
V
4 2
.
V
.
+
⎞
⎟ −
⎠
HB
V
)
0 004
.
⎞
⎟ −
⎠
−
1
1 24
⎤
⎥
⎥
⎦
.
R
⎞
⎟ −
⎠
1
M
Ω
1
⎤
⎥
⎥
⎦
For this example, choose a 499kΩ standard value 1%
resistor.
4) Calculate R3:
5) Verify the resistor values. The equations are as fol-
where the internal hysteresis band, V
Figure 5 shows a zero-crossing detector application.
The MAX9015/MAX9016/MAX9019/MAX9020s’ invert-
ing input is connected to ground, and its noninverting
input is connected to a 100mV
signal at the noninverting input crosses zero, the com-
parator’s output changes state.
Figure 4. Window Detector Circuit
R1
R3
R2
lows, evaluated for the above example:
Overvoltage threshold:
Undervoltage threshold:
V
V
V
OTH
UTH
IN
V
V
OTH
UTH
=
=
= 4.2V
= 2.9V
(
(
V
V
INA+
REF/INA-
INB+
INB-
REF
REF
1.24V
R3 = (R2 + R3) - R2
REF
V
+
−
EE
V
= 2.95MΩ - 546kΩ
= 240MΩ
V
HB
HB
)
)
Zero-Crossing Detector
V
V
V
5V
x
x
CC
CC
EE
(
(
R
R
1
P-P
1
MAX9018
(
R
+
+
1
signal source. As the
R
R
R
+
2
2
1
HB
R
+
+
2
OUTA
OUTB
, is 4mV.
R
R
)
3
3
)
)
=
=
2 97
4 20
.
.
POWER-
GOOD
V
V