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TMS320F280049: ECAP electrical characteristics and noise immunity

Sheldon He
Expert 8585 points
Part Number: TMS320F280049


Hi expert,

My customer meet a case where ECAP being influenced by external noise and get wrong capture result. They would like to solve this issue with GPIO qualification and change paramters in external circuit.

In idea situation, CH1 is external input signal, they detect this signal and output it to GPIO28 (CH2) to know the "input signal state".

In real situation, glitches can be seen in the capture result, and the influence of glitch is also indicated with GPIO toggling.

They solved this with GPIO input qualification. Configuration shown below:

Based on this, we'd like to confirm below questions:

1. Does ECAP comply to below electrical characteristics? How does it detect external voltage? (like with a majority vote or directly trigger with voltage level?)

2. What will input state be judged when voltage is between 0.8V to 2V? How will hysteresis influcence here?

Thanks

Sheldon

  • 0
    TI__Mastermind 26400 points

    The expert this issue is assigned to is Out of office. Please expect a reply on Monday.

  • 0
    TI__Mastermind 28275 points

    Hi Sheldon,

    I'm not able to read the grids on your scope shots to figure out the signal levels but to answer your questions:

    1. Yes, the input levels also apply to the ECAP. VIH(min) is the minimum your input should be to guarantee a logic 1 by the device. VIL(max) is the maximum your input should be to guarantee a logic 0 by the device. The delta between VIH(min) and VIL(max) is essentially the maximum hysteresis you can expect.

    2. The region between 0.8v and 2v is "no man's land". It's also the hysteresis region as described above. Between 0.8v and 2v, the signal will be recognized as either a logic 1 or a logic 0. The problem is you don't know which one it will be. The VOH of your source should be greater than VIH(min) of the device and VOL less than VIL(max) to guarantee correct interfacing between the 2 circuits. The Vhysteresis parameter (150mV) is essentially the minimum hysteresis you can expect.