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AP393

LOW POWER LOW OFFSET VOLTAGE DUAL COMPARATORS

Diodes Incorporated. 

Application Information

AP393

LOW POWER LOW OFFSET VOLTAGE DUAL

COMPARATORS

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 < 10kΩ 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 supply voltage over the

range of from 2.0 VDC to 30 VDC. It is usually unnecessary to use a bypass capacitor across the power supply line.

The differential input voltage may be larger than V+ without damaging the device (Note 8). Protection should be provided to

prevent the input voltages from going negative more than -0.3 VDC (at 25°C). An input 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+

terminal of the AP393 package. The output can 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+) and the β of this device.

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 60Ω rSAT of the output transistor. The low offset voltage

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

Typical Circuit ( VCC = 5.0VDC )

V+

+5.0VDC

+VIN

+VREF

+

AP393

-

3.0K

VO

Basic Comparator

+5VDC

+

AP393

-

10K

1/4 DM54XX

Driving TTL

+

AP393

-

100K

1/4 MM54CXX

Driving CMOS

V+

100K

75 pF

-

1/2 AP393

+

100K

V+

100K

100K

4.3K

V+

0

1:100kHz

VO

Squarewave Oscillator

AP393 Rev. 3

6 of 15

www.diodes.com

FEBRUARY 2007

© Diodes Incorporated

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