AP331A

SINGLE DIFFERENTIAL COMPARATOR

AP331A Rev. 2

5 of 13

FEBRUARY 2009

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Application Information

The AP331A is high gain, wide bandwidth devices, like most comparators, can easily oscillate if the output lead is inadvertently

allowed to capacitively couple to the inputs via stray capacitance. This shows up only during the output voltage transition intervals as the

comparator change states. Power supply bypassing is not required to solve this problem. Standard PC board layout is helpful as it

reduces stray input-output coupling. Reducing the input resistors to < 10k

Ω reduces the feedback signal levels and finally, adding even a

small amount (1.0 to 10 mV) of positive feedback (hysteresis) causes such a rapid transition that oscillations due to stray feedback are

not possible. Simply socketing the IC and attaching resistors to the pins will cause input-output oscillations during the small transition

intervals unless hysteresis is used. If the input signal is a pulse waveform, with relatively fast rise and fall times, hysteresis is not required.

All input pins of any unused comparators should be tied to the negative supply.

The bias network of the AP331A establishes a drain current independent of the magnitude of the power supply voltage over the

The differential input voltage may be larger than V+ without damaging the device (Note 10). Protection should be provided to

applications section.

The output of the AP331A is the uncommitted collector of a grounded-emitter NPN output transistor. Many collectors can be tied

together to provide an output OR’ing function. An output pull-up resistor can be connected to any available power supply voltage within

the permitted supply voltage range and there is no restriction on this voltage due to the magnitude of the voltage applied to the

V

The amount of current the output device can sink is limited by the drive available (which is independent of V

When the maximum current limit is reached (approximately 16mA), the output transistor will come out of saturation and the output voltage

will rise very rapidly. The output saturation voltage is limited by the approximately 60

of the output transistor (1.0 mV) allows the output to clamp essentially to ground level for small load currents.

Typical Circuit

3.0K

+

-

+

-

100K

1/4 MM54CXX