LM2903EP
Output Saturation Voltage
Response Time for Various Input Overdrives—Negative
Transition
20114133
20114132
Response Time for Various Input Overdrives—Positive
Transition
20114134
Application Hints
The LM2903EP is a high gain, wide bandwidth device 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 volt-
age 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 kΩ
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 at-
taching resistors to the pins will cause input-output oscilla-
tions 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 LM2903EP establishes a drain cur-
rent which is independent of the magnitude of the power
supply voltage over the range of from 2.0 V
DC
to 30 V
DC
.
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
Protection should be provid-
ed to prevent the input voltages from going negative more
than −0.3 V
DC
(at 25°C). An input clamp diode can be used
as shown in the applications section.
The output of the LM2903EP 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 which is applied to the V
+
terminal
of the LM2903EP 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
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 ap-
proximately 60Ω r
SAT
of the output transistor. The low offset
5
201141 Version 3 Revision 1
Print Date/Time: 2009/09/29 16:01:39
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