Datasheet

MAX9015–MAX9020
SOT23, Dual, Precision, 1.8V, Nanopower
Comparators With/Without Reference
14
Maxim Integrated
Board Layout and Bypassing
The MAX9015–MAX9020 ultra-low supply current typical-
ly 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
CC
to V
EE
with a 0.1µF capacitor placed as close to the V
CC
pin as possible. Minimize signal trace lengths to reduce
stray capacitance. Use a ground plane and surface-
mount components for best performance. If REF is
decoupled, use a low-leakage ceramic capacitor. High
traces should not be routed in the vicinity of or below
MAX9018. There is a chance of voltage reference being
overloaded resulting in drop of output voltage.
Window Detector
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 nominal value
of 3.6V. Choose different thresholds by changing the val-
ues of R1, R2, and R3. OUTA provides an active-low
undervoltage indication, and OUTB provides 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-
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).
2) Calculate R2 + R3. The overvoltage threshold
should be 4.2V when V
IN
is rising. The design
equation is as follows:
=2.95MΩ
3) Calculate R2. The undervoltage threshold should
be 2.9V when V
IN
is falling. The design equation is
as follows:
= 546kΩ
For this example, choose a 499kΩ standard value 1%
resistor.
4) Calculate R3:
R3 = (R2 + R3) - R2
= 2.95MΩ - 546kΩ
= 240MΩ
5) Verify the resistor values. The equations are as fol-
lows, evaluated for the above example:
Overvoltage threshold:
Undervoltage threshold:
where the internal hysteresis band, V
HB
, is 4mV.
Zero-Crossing Detector
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
P-P
signal source. As the
signal at the noninverting input crosses zero, the com-
parator’s output changes state.
VVVx
RRR
RR
V
UTH REF
HB
=−
++
+
=()
()
()
.
123
12
297
VVVx
RRR
R
V
OTH REF
HB
=+
++
=()
()
.
123
1
420
=Ω+Ω −Ω(. . )
(. )
.
.124 295
1 236
29
124MMx M
RRRRx
VV
V
R
REF
HB
UTH
2123 1=++
−
⎛
⎝
⎜
⎞
⎠
⎟
−()
=Ω
+
⎛
⎝
⎜
⎞
⎠
⎟
−
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
124
42
1 24 0 004
1.
.
..
Mx
V
V
RRRx
V
VV
OTH
REF
HB
231 1+=
+
⎛
⎝
⎜
⎞
⎠
⎟
−
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
MAX9018
V
CC
INA+
OUTA
V
CC
V
EE
REF/INA-
REF
1.24V
INB+
INB-
OUTB
V
EE
V
IN
V
OTH
= 4.2V
V
UTH
= 2.9V
R3
R2
R1
5V
POWER-
GOOD
Figure 4. Window Detector Circuit