LM139/LM239/LM339/LM2901/LM3302

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7

Application Hints

The LM139 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 changes 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

this input resistors to <10kΩ reduces the feedback signal levels and

finally, adding even a small amount (1 to 10m V) of positive

feedback (hysteresis) causes such a repid 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 pins of any unused comparators should be tied to the negative

supply.

The bias network of the LM139 series establishes a drain current

which is independent of the magnitude of the power supply voltage

It is usually unnecessary to use a bypass capacitor across the

power supply line.

The differential input voltage may be larger than V

damaging the device. Protection should be provided to prevent the

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

The output of the LM139 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 be permitted supply voltage range and there is no restriction

on this voltage due to the magnitude of the voltage which is applied

to the V

used as a simple SPST switch to ground (when a pull-up resistor is

not used). The amount of current which the output device can sink is

limited by the drive available (which is independent of V

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

output transistor. The low offset voltage of the output transistor

(1mV) allows the output to clamp essentially to ground level for

small load currents.

Basic Comparator

00570603

Driving CMOS

00570604

Driving TTL

00570604

AND Gate

OR Gate