Application Hints
The LM193 series are high gain, wide bandwidth devices
which, like most comparators, can easily oscillate if the out-
put 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 re-
sistors to k10 kXreduces the feedback signal levels and
finally, adding even a small amount (1.0 to 10 mV) of posi-
tive feedback (hysteresis) causes such a rapid transition
that oscillations due to stray feedback are not possible. Sim-
ply socketing the IC and attaching resistors to the pins will
cause input-output oscillations during the small transition in-
tervals unless hysteresis is used. If the input signal is a
pulse waveform, with relatively fast rise and fall times, hys-
teresis is not required.
All pins of any unused comparators should be grounded.
The bias network of the LM193 series establishes a drain
current which is 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 Vawithout
damaging the device (see Note 8). Protection should be
provided to prevent the input voltages from going negative
more than b0.3 VDC (at 25§C). 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 collec-
tors can be tied together to provide an output OR’ing func-
tion. 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 which is applied to the Va
terminal of the LM193 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 which the output
device can sink is limited by the drive available (which is
independent of Va) and the bof this device. When the
maximum current limit is reached (approximately 16 mA),
the output transistor will come out of saturation and the out-
put voltage will rise very rapidly. The output saturation volt-
age is limited by the approximately 60XrSAT 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 Applications (Vae5.0 VDC)
Basic Comparator Driving CMOS Driving TTL
TL/H/5709–2
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