Leakage Current vs. Supply Voltage

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Application Information

1.0 BENEFITS OF THE LMC7221 TINY COMPARATOR

Size

The small footprint of the 5-Pin SOT23 packaged Tiny Com-

parator, (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 LMC7221 extends

battery life in portable applications, and may allow the reduc-

tion of the size of batteries in some applications.

Wide Voltage Range

The LMC7221 is characterized at 15V, 5V and 2.7V. Perfor-

mance data is provided at these popular voltages. This wide

voltage range makes the LMC7221 a good choice for de-

vices where the voltage may vary over the life of the batter-

ies.

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 micro-

processors and other digital circuits. The LMC7221 can be

thought of as a one-bit a/d converter.

Open Drain Output

The open drain output is like the open collector output of a

logic gate. This makes the LMC7221 very useful for mixed

voltage systems.

Driving LEDs (Light Emitting Diodes)

With a 5 volt power supply, the LMC7221’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 LMC7221 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, am-

plifiers, 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 LMC7221’s common mode input range extends

below ground even when powered by a single positive sup-

ply, it can be used with large input resistors as a zero

crossing detector.

Low Input Currents and High Input Impedance

These characteristics allow the LMC7221 to be used to

sense high impedance signals from sensors. They also

make it possible to use the LMC7221 in timing circuits built

with large value resistors. This can reduce the power dissi-

pation 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.

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