AP393

LOW POWER LOW OFFSET VOLTAGE DUAL

COMPARATORS

AP393

Document number: DS31006 Rev. 8 - 2

12 of 15

www.diodes.com

July 2010

© Diodes Incorporated

Application Information

The AP393 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 AP393 establishes a drain current independent of the magnitude of the power

across the power supply line.

The differential input voltage may be larger than V+ without damaging the device (Note 11). Protection

clamp diode can be used as shown in the applications section.

The output of the AP393 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

also be used as a simple SPST switch to ground (when a pull-up resistor is not used). 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

Ω r

output to clamp essentially to ground level for small load currents.