LMC7211-N_14 Datasheet, PDF (13/23 Pages) Texas Instruments – LMC7211 Tiny CMOS Comparator with Rail-to-Rail Input and Push-Pull Output

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LMC7211-N
SNOS746F – MAY 2004 – REVISED JANUARY 2013
Figure 8. With Positive Feedback (Hysteresis or Memory)
Input Protection
If input signals are like to exceed the common mode range of the LMC7211, or it is likely that signals may be
present when power is off, damage to the LMC7211 may occur. Large value (100 kΩ to MΩ) input resistors may
reduce the likelihood of damage by limiting the input currents. Since the LMC7211 has very low input leakage
currents, the effect on accuracy will be small. Additional protection may require the use of diodes, as shown in
Figure 9. Note that diode leakage current may affect accuracy during normal operation. The R-C time constant of
R_IN and the diode capacitance may also slow response time.
Figure 9.
Layout Considerations
The LMC7211 is not an especially fast comparator, so high speed design practices are not required. The
LMC7211 is capable of operating with very high impedance inputs, so precautions should be taken to reduce
noise pickup with high impedance (∼ 100 kΩ and greater) designs and in electrically noisy environments.
Keeping high value resistors close to the LMC7211 and minimizing the size of the input nodes is a good practice.
With multilayer designs, try to avoid long loops which could act as inductors (coils). Sensors which are not close
to the comparator may need twisted pair or shielded connections to reduce noise.
Open Drain Output, Dual Versions
The LMC7221 is a comparator similar to the LMC7211, but with an open drain output which allows the output
voltage to be different (higher or lower) than the supply voltage. The open drain output is like the open collector
output of a logic gate. This makes the LMC7221 very useful for mixed voltage systems. Many systems will have
different voltages for the analog and microprocessor sections. Please see the LMC7221 datasheet for details.
The performance of the LMC7211 is available in dual devices. Please see the LMC6762 datasheet for details on
a dual push-pull output device. For a dual device with open drain outputs, please see the LMC6772 datasheet.
Rail-to-Rail Input Low Power Comparators—
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