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Hysteresis: LTC6702 MAX9021 MAX9031

Hysteresis is a property of comparators that prevents rapid output changes when the input voltage is near zero. It introduces two switching points rather than one - one for rising voltages and one for falling voltages. The difference between the higher and lower trip values equals the hysteresis voltage. If a comparator does not have internal hysteresis or noise is greater than internal hysteresis, an external hysteresis network can be added using positive feedback. Some comparators also provide a separate hysteresis pin to allow programmable hysteresis without feedback. With hysteresis, a comparator cannot resolve signals within the hysteresis band.

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Arun Gopinath
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117 views1 page

Hysteresis: LTC6702 MAX9021 MAX9031

Hysteresis is a property of comparators that prevents rapid output changes when the input voltage is near zero. It introduces two switching points rather than one - one for rising voltages and one for falling voltages. The difference between the higher and lower trip values equals the hysteresis voltage. If a comparator does not have internal hysteresis or noise is greater than internal hysteresis, an external hysteresis network can be added using positive feedback. Some comparators also provide a separate hysteresis pin to allow programmable hysteresis without feedback. With hysteresis, a comparator cannot resolve signals within the hysteresis band.

Uploaded by

Arun Gopinath
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Hysteresis[edit]

A comparator normally changes its output state when the voltage between its inputs crosses through
approximately zero volts. Small voltage fluctuations due to noise, always present on the inputs, can
cause undesirable rapid changes between the two output states when the input voltage difference is
near zero volts. To prevent this output oscillation, a small hysteresis of a few millivolts is integrated
into many modern comparators.[8] For example, the LTC6702, MAX9021 and MAX9031 have internal
hysteresis desensitizing them from input noise. In place of one switching point, hysteresis introduces
two: one for rising voltages, and one for falling voltages. The difference between the higher-level trip
value (VTRIP+) and the lower-level trip value (VTRIP-) equals the hysteresis voltage (VHYST).
If the comparator does not have internal hysteresis or if the input noise is greater than the internal
hysteresis then an external hysteresis network can be built using positive feedback from the output
to the non-inverting input of the comparator. The resulting Schmitt trigger circuit gives additional
noise immunity and a cleaner output signal. Some comparators such
as LMP7300, LTC1540, MAX931, MAX971 and ADCMP341 also provide the hysteresis control
through a separate hysteresis pin. These comparators make it possible to add a programmable
hysteresis without feedback or complicated equations. Using a dedicated hysteresis pin is also
convenient if the source impedance is high since the inputs are isolated from the hysteresis network.
[9]
 When hysteresis is added then a comparator cannot resolve signals within the hysteresis band.

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