TLV3201 Question

Hi Ian,

I went over your hysteresis calculations that are based on the information in the TLV3201 data sheet. Your calculations are correct, but the VIN1 equation (4) listed is not correct and results in an incorrect high therehold level. Equation (5) for VIN2, the low threhold, and equation (6) for ∆VIN, the hysteresis voltage, are correct.

The LMV7271, a comparator from SVA, has in its data sheet Application Notes section the correct equation for VIN1, on page 14: http://www.ti.com/lit/ds/symlink/lmv7271.pdf

VIN1 = VREF (R1 + R2) / R2

Using this equation, VN1 is 3.325 V, VN2 equal to 1.675 V and  ∆VIN, the hysteresis, is 1.65 V. This is the same hysteresis voltage that is obtained using equation (6) above. This is a large hysteresis voltage and often it is set to 5 to 50 mV, as mentioned in the LMV7271 Hysteresis section.

Hysteresis is an intentional voltage offset that is introduced into the comparator circuit to separate the rising and falling edge comparison points apart. If they are identical, any noise riding on a voltage right at the comparator threshold point where it makes comparison, can cause the output of the comparator to rapidly switch states in response to noise fluxuations. Moving the rising and falling thresholds provides noise immunity to the input voltage comparison.

TI Design, TIPD122, provides much information about the role hysteresis plays in comparator circuits. I recommend you have look at it:

http://www.ti.com/lit/ug/tidu020a/tidu020a.pdf

Regards, Thomas

PA - Linear Applications Engineering