Datasheet

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MAX44269
1.3mm x 1.3mm, Low-Power
Dual Comparator
Ordering Information
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
Window Detector Circuit
The IC is ideal for window detectors (undervoltage/over-
voltage detectors). Figure 10 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 values
of R1, R2, and R3. OUTA provides an active-low under-
voltage indication, and OUTB provides an active-low
overvoltage indication. The open-drain outputs of both
the comparators are wired OR to give an active-high
power-good signal.
The design procedure is as follows:
1) Select R1. The input bias current into INB- is less than
15nA, so the current through R1 should exceed 1.5µA
for the thresholds to be accurate. In this example,
choose R1 = 825kI (1.24V/1.5µA).
2) Calculate R2 + R3. The overvoltage threshold should
be 4.2V when V
IN
is rising. The design equation is as
follows:
OTH
REF
V
R2 R3 R1 x 1
V
4.2
825 x 1
1.24
=1969k


+= −







= −




Ω
3) Calculate R2. The undervoltage threshold should be
2.9V when V
IN
is falling. The design equation is as
follows:
( ) ( )
( )
REF
UTH
V
R2 (R1 R2 R3)x R1
V
825 1969 x 1.24 / 2.9 825
370k

=++ −


=+−
= Ω
For this example, choose a 374kI standard value 1%
resistor.
4) Calculate R3:
R3 (R2 R3) R2
1969k 374k
=1.595M
=+−
= Ω− Ω
Ω
For this example, choose a 1.58MI standard value 1%
resistor.
Board Layout and Bypassing
Use 1.0FF bypass capacitors from V
CC
to GND. To maxi-
mize performance, minimize stray inductance by putting
this capacitor close to the V
CC
pin and reducing trace
lengths.
Figure 10. Window Detector Circuit
Chip Information
PROCESS: BiCMOS
PART TEMP RANGE
PIN-
PACKAGE
TOP
MARK
MAX44269EWL+T
-40NC to +85NC
9 WLP +AJL
V
CC
5V
V
IN
INB+
INA+
V
OTH
= 4.2V
V
UTH
= 2.9V
INA-
INB-
GND
R1
R2
R3
GND
OUTB
OUTA
POWER
GOOD
MAX44269
REF
1.24V