LMC7211AIM5X Datasheet, PDF (12/22 Pages) Texas Instruments – LMC7211 Tiny CMOS Comparator with Rail-to-Rail Input and Push-Pull Output

LMC7211-N
SNOS746F – MAY 2004 – REVISED JANUARY 2013
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Output Short Circuit Current
The LMC7211 has short circuit protection of 40 mA. However, it is not designed to withstand continuous short
circuits, transient voltage or current spikes, or shorts to any voltage beyond the supplies. A resistor in series with
the output should reduce the effect of shorts. For outputs which send signals off PC boards additional protection
devices, such as diodes to the supply rails, and varistors may be used.
Hysteresis
If the input signal is very slow or very noisy, the comparator output might trip several times as the input signal
passes through the threshold. Using positive feedback to add hysteresis to the switching can reduce or eliminate
this problem. The positive feedback can be added by a high value resistor (R_F). This will result in two switching
thresholds, one for increasing signals and one for decreasing signals. A capacitor can be added across R_F to
increase the switching speed and provide more short term hysteresis. This can result in greater noise immunity
for the circuit.
See Figure 6, Figure 7 and Figure 8.
Note that very heavy loading of the comparator output, such as LED drive or bipolar logic gates, will change the
output voltage and shift the voltage thresholds.
R_F ≫ R₁ and
R_F ≫ R₂
Figure 6. Positive Feedback for Hysteresis
Figure 7. Without Positive Feedback (No Hysteresis)
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