LMC7211-N

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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 k

Ω 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

RIN 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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