• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 82 subscribers
  • Views 431 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

f28035 COMP1A input impedance problem

Tufan Karalar
Prodigy 20 points

Hi all,

I use the F28035 on a evaluation board TMDXDOCK28035 Experimenter's kit. I use AIO2 input to connect an analog signal to COMP1A's input. When comparator output is 0, then at the comparator input( i.e AIO2),  I measure a 100K resistance to ground, when output is 1, 100K resistance to supply. I am assuming that it is because of the Comparator hysteresis input which is specified to be 35mV. when I use a 50K source resistance, input hysteresis is about 300-400mV. what is theexpected source resistance to achieve this 35mV hysteresis?

Thank you for the help.

Tufan

  • 0
    TI__Guru* 84290 points

    Tufan,

    You measurement is correct, the hysteresis is implemented via a Schmidt trigger with 100kOhm feedback resistor between output and pos input.  There is also ~1k switch resistor in series with pos input of the comparator.

    Just want to ask if the hysteresis is changing, or since your 50k is of same magnitude as 100k, that it is changing the voltage on the node, depending on the output state of the comparator(high or low).

    I will be documenting the trigger and resistances in a new revision of the ADC/COMP user's guide.

    With regards to proper values outside the chip I'd try and stay below 10k/5k range.

    Best,

    Matthew