LMC7211-N
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SNOS746F –MAY 2004–REVISED JANUARY 2013
APPLICATION INFORMATION
Benefits of the LMC7211 Tiny Comparator
Size. The small footprint of the SOT 23-5 packaged Tiny Comparator, (0.120 x 0.118 inches, 3.05 x 3.00 mm)
saves space on printed circuit boards, and enable the design of smaller electronic products. Because they are
easier to carry, many customers prefer smaller and lighter products.
Height. The height (0.056 inches, 1.43 mm) of the Tiny Comparator makes it possible to use it in PCMCIA type
III cards.
Simplified Board Layout. The Tiny Comparator can simplify board layout in several ways. First, by placing a
comparator where comparators are needed, instead of routing signals to a dual or quad device, long pc traces
may be avoided.
By using multiple Tiny Comparators instead of duals or quads, complex signal routing and possibly crosstalk can
be reduced.
Low Supply Current. The typical 7 μA supply current of the LMC7211 extends battery life in portable
applications, and may allow the reduction of the size of batteries in some applications.
Wide Voltage Range. The LMC7211 is characterized at 15V, 5V and 2.7V. Performance data is provided at
these popular voltages. This wide voltage range makes the LMC7211 a good choice for devices where the
voltage may vary over the life of the batteries.
Digital Outputs Representing Signal Level. Comparators provide a high or low digital output depending on the
voltage levels of the (+) and (−) inputs. This makes comparators useful for interfacing analog signals to
microprocessors and other digital circuits. The LMC7211 can be thought of as a one-bit a/d converter.
Push-Pull Output. The push-pull output of the LMC7211 is capable of both sourcing and sinking milliamp level
currents even at a 2.7 volt supply. This can allow the LMC7211 to drive multiple logic gates.
Driving LEDs (Light Emitting Diodes). With a 5 volt power supply, the LMC7211's output sinking current can
drive small, high efficiency LEDs for indicator and test point circuits. The small size of the Tiny package makes it
easy to find space to add this feature to even compact designs.
Input range to Beyond Rail to Rail. The input common mode range of the LMC7211 is slightly larger than the
actual power supply range. This wide input range means that the comparator can be used to sense signals close
to the power supply rails. This wide input range can make design easier by eliminating voltage dividers,
amplifiers, and other front end circuits previously used to match signals to the limited input range of earlier
comparators. This is useful to power supply monitoring circuits which need to sense their own power supply, and
compare it to a reference voltage which is close to the power supply voltage. The wide input range can also be
useful for sensing the voltage drop across a current sense resistor for battery chargers.
Zero Crossing Detector. Since the LMC7211's common mode input range extends below ground even when
powered by a single positive supply, it can be used with large input resistors as a zero crossing detector.
Low Input Currents and High Input Impedance. These characteristics allow the LMC7211 to be used to sense
high impedance signals from sensors. They also make it possible to use the LMC7211 in timing circuits built with
large value resistors. This can reduce the power dissipation of timing circuits. For very long timing circuits, using
high value resistors can reduce the size and cost of large value capacitors for the same R-C time constant.
Direct Sensor Interfacing. The wide input voltage range and high impedance of the LMC7211 may make it
possible to directly interface to a sensor without the use of amplifiers or bias circuits. In circuits with sensors
which can produce outputs in the tens to hundreds of millivolts, the LMC7211 can compare the sensor signal
with an appropriately small reference voltage. This may be done close to ground or the positive supply rail. Direct
sensor interfacing may eliminate the need for an amplifier for the sensor signal. Eliminating the amplifier can
save cost, space, and design time.
Low Voltage Operation
Comparators are the common devices by which analog signals interface with digital circuits. The LMC7211 has
been designed to operate at supply voltages of 2.7V without sacrificing performance to meet the demands of 3V
digital systems.
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