LM193A, LM193QML

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SNOSAM2C – MAY 2005 – REVISED MARCH 2013

APPLICATION HINTS

The LM193 series are high gain, wide bandwidth devices which, 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 < 10 K

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 LM193 series establishes a drain current which is independent of the magnitude of the

It is usually unnecessary to use a bypass capacitor across the power supply line.

NOTE

Positive excursions of input voltage may exceed the power supply level. As long as the

other voltage remains within the common-mode range, the comparator will provide a

proper output state. The low input voltage state must not be less than

−0.3V (or 0.3V

below the magnitude of the negative power supply, if used).

Protection should be provided to prevent the input voltages from going negative more than

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

The output of the LM193 series 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

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

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 60

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

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Product Folder Links: LM193A LM193QML