LMC7221AIM National Semiconductor, LMC7221AIM Datasheet - Page 8

• Manufacturer Part Number: LMC7221AIM
• Description: Voltage Comparator IC
• Manufacturer: National Semiconductor

Specifications of LMC7221AIM

• No. Of Comparators: 1
• Response Time: 8000ns
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +85°C
• Peak Reflow Compatible (260 C): No
• Output Type: CMOS
• No. Of Circuits: 1
• Leaded Process Compatible: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Application Information
Direct Sensor Interfacing
The wide input voltage range and high impedance of the
LMC7221 may make it possible to directly interface to a
sensor without the use of amplifiers or bias circuits. In cir-
cuits with sensors which can produce outputs in the tens to
hundreds of millivolts, the LMC7221 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.
2.0 LOW VOLTAGE OPERATION
Comparators are the common devices by which analog sig-
nals interface with digital circuits. The LMC7221 has been
designed to operate at supply voltages of 2.7V without sac-
rificing performance to meet the demands of 3V digital sys-
tems.
At supply voltages of 2.7V, the common-mode voltage range
extends 200 mV (guaranteed) below the negative supply.
This feature, in addition to the comparator being able to
sense signals near the positive rail, is extremely useful in low
voltage applications.
At V
4 µs with overdrives of 100 mV.
Please refer to the performance curves for more extensive
characterization.
FIGURE 1. Even at Low-Supply Voltage of 2.7V, an
Input Signal which Exceeds the Supply Voltages
+
= 2.7V propagation delays are t
Produces No Phase Inversion at the Output
PLH
= 4 µs and t
(Continued)
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PHL
=
8
3.0 OPEN DRAIN OUTPUT
Figure 2 shows the difference between push-pull output and
open drain output.
Push pull outputs will have a conventional high or low digital
output, the same as a logic gate. Low will be the negative
supply rail (usually ground) and high will be the positive
supply rail.
This is useful if the chips you are interfacing to run on the
same supply voltage as the comparator. An example would
be an all +5V system.
Open drain outputs will only pull low — for the high output
they depend on an external pull-up resistor. This can pull up
to a voltage higher or lower than the comparator supply
voltage. This voltage can be as high as 15V. This makes the
open drain parts useful in mixed voltage systems. An ex-
ample would be where the comparator runs at 5V and the
logic circuits are at 3.3V. The pull-up resistor would go to the
3.3V supply.
Open drain outputs are the CMOS equivalent of open col-
lector outputs.
Output Stage
FIGURE 2.
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