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LM2903N Datasheet(PDF) 11 Page - Texas Instruments

Part No. LM2903N
Description  Low-Power, Low-Offset Voltage, Dual Comparators
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Manufacturer  TI1 [Texas Instruments]
Direct Link  http://www.ti.com
Logo TI1 - Texas Instruments

LM2903N Datasheet(HTML) 11 Page - Texas Instruments

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LM193-N, LM2903-N, LM293-N, LM393-N
9 Application and Implementation
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The LM193 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 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 k
Ω 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 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 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.
The differential input voltage may be larger than V+ without damaging the deviceTypical Applications . Protection
should be provided to prevent the input voltages from going negative more than
−0.3 VDC (at 25°C). An input
clamp diode can be used as shown in Typical Applications .
The output of the LM193 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 pullup 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 LM193 package. The
output can also be used as a simple SPST switch to ground (when a pullup 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
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 60
Ω 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.
9.2 Typical Applications
9.2.1 Basic Comparator
Figure 12. Basic Comparator Design Requirements
The basic usage of a comparator is to indicate when a specific analog signal has exceeded some predefined
threshold. In this application, the negative input (IN–) is tied to a reference voltage, and the positive input (IN+) is
connected to the input signal. The output is pulled up with a resistor to the logic supply voltage, V+ with a pullup
For an example application, the supply voltage is 5V. The input signal varies between 1 V and 3 V, and we want
to know when the input exceeds 2.5 V±1%. The supply current draw should not exceed 1 mA.
Copyright © 1999–2014, Texas Instruments Incorporated
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Product Folder Links: LM193-N LM2903-N LM293-N LM393-N

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