Detailed Description
The MAX9065 is an extremely small window compara-
tor designed for compact, low-current applications, fea-
turing a supply current of less than 1µA (max).
Operation
At the heart of the MAX9065 are two comparators, a
resistor-divider with a disconnect switch, a 200mV ref-
erence, digital logic circuitry, and an output stage (see
the
Typical Operating Circuit
).
The digital logic circuitry and the output stage together
behave like an AND gate. The gate’s inputs are the out-
puts of the two comparators. When either comparator’s
output is low, the output asserts low. When both com-
parator’s outputs are high, the output asserts high.
When power is applied to VCC, the n-channel FET at
the bottom of the resistor-divider is turned on. The
resistor-divider provides two voltages, VUPPER and
VLOWER, for comparison with an internal 0.2V reference
voltage. When the input voltage exceeds 4.2V, VUPPER
is greater than 0.2V, causing the output to assert low.
When the input voltage falls below 3.0V, VLOWER is less
than 0.2V, causing the output also to assert low. With
the input voltage between 3.0V and 4.2V, the output
asserts high, indicating that the input voltage is within
the desired range. Table 1 summarizes the operation of
the MAX9065.
When VCC goes to 0V, the n-channel FET is turned off,
eliminating the resistor-divider as a leakage path for
current.
Applications
The MAX9065 is designed specifically to monitor the
voltage on a single lithium battery. Keeping the voltage
on a lithium battery within a tight range is important to
prevent damage to the battery. Specifically, ensuring
that the battery’s voltage neither exceeds 4.2V nor falls
below 3.0V lengthens the lifetime of the battery and
avoids any hazardous battery conditions.
Hysteresis
There are four trip points for hysteresis. See Figure 1.
Power-Supply Considerations
Bypass VCC with a 0.1µF capacitor to ground.
Chip Information
PROCESS: BiCMOS
MAX9065
Ultra-Small, Low-Power, Window Comparator
in 4 UCSP and 5 SOT23
_______________________________________________________________________________________ 5
Pin Description
External Supply Input. Bypass
capacitor.