lm2903ep National Semiconductor Corporation, lm2903ep Datasheet - Page 6

• Manufacturer Part Number: lm2903ep
• Description: Low Power Low Offset Voltage Dual Comparators
• Manufacturer: National Semiconductor Corporation

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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
voltage transition intervals as the comparator change states.
Power supply bypassing is not required to solve this prob-
lem. Standard PC board layout is helpful as it reduces stray
input-output coupling. Reducing the input resistors to
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 LM2903EP establishes a drain
current which is independent of the magnitude of the power
supply voltage over the range of from 2.0 V
It is usually unnecessary to use a bypass capacitor across
the power supply line.
Typical Applications
<
10 kΩ reduces the feedback signal levels and finally,
Squarewave Oscillator
Basic Comparator
20114135
20114138
(V
+
=5.0 V
* For large ratios of R1/R2,
D1 can be omitted.
DC
DC
to 30 V
) (Note 15)
DC
Pulse Generator
Driving CMOS
.
6
The differential input voltage may be larger than V
damaging the device (Note 12). Protection should be pro-
vided to prevent the input voltages from going negative more
than −0.3 V
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
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 indepen-
dent of V
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 60Ω r
low offset voltage of the output transistor (1.0mV) allows the
output to clamp essentially to ground level for small load
currents.
20114136
+
20114139
) and the β of this device. When the maximum
DC
(at 25˚C). An input clamp diode can be used
Crystal Controlled Oscillator
SAT
of the output transistor. The
Driving TTL
+
20114137
+
terminal
20114140
without