LM193-N, LM2903-N, LM293-N, LM393-N

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SNOSBJ6F – OCTOBER 1999 – REVISED DECEMBER 2014

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

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

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

clamp diode can be used as shown in Typical Applications .

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 pullup 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 pullup 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.

9.2 Typical Applications

9.2.1 Basic Comparator

Figure 12. Basic Comparator

9.2.1.1 Design Requirements

The basic usage of a comparator is to indicate when a specific analog signal has exceeded some predefined

threshold. In this application, the negative input (IN–) is tied to a reference voltage, and the positive input (IN+) is

connected to the input signal. The output is pulled up with a resistor to the logic supply voltage, V+ with a pullup

resistor.

For an example application, the supply voltage is 5V. The input signal varies between 1 V and 3 V, and we want

to know when the input exceeds 2.5 V±1%. The supply current draw should not exceed 1 mA.

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Product Folder Links: LM193-N LM2903-N LM293-N LM393-N