LM2901Q/LM2901AQ/LM2903Q/LM2903AQ
Document number: DS37814 Rev. 2 - 2
June 2016
© Diodes Incorporated
LM2901Q/ LM2901AQ/
LM2903Q/ LM2903AQ
Application Information
General Information
The LM2901Q/2903Q series comparators are high-gain, wide-bandwidth devices, and like most comparators, can easily oscillate if the output lead
is inadvertently allowed to capacitive couple to the inputs via stray capacitance. This shows up only during the output voltage transition intervals as
the comparator changes states. Standard PC board layout is helpful as it reduces stray input-output coupling. Reducing the input resistors to
<10kΩ reduces the feedback signal levels and finally, adding even a small amount (1.0 to 10mV) 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 LM2901Q/2903Q series comparators establishes a quiescent current independent of the magnitude of the power supply
voltage over the range of from 2.0 VDC to 30 VDC.
The differential input voltage may be larger than VCC without damaging the device. Protection should be provided to prevent the input voltages from
becoming negative more than -0.3 VDC (@ +25°C). An input clamp diode can be used as shown in the applications section.
The output of the LM2901Q/2903Q series comparators 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 applied to the VCC terminal of
LM2901/2903 series comparator 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 the output device can sink is limited by the drive available (which is independent of VCC) 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 approximately 60Ω RSAT of the output transistor. The low offset voltage of the output
transistor (1.0mV) allows the output to clamp essentially to ground level for small load currents.