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TMCS1126: OC pin maximum allowed sink current

Olli Pokkinen
Prodigy 40 points
Part Number: TMCS1126


Tool/software:

Hi,

What is the max. recommended sink current for the OC pin?

BR,

Olli

  • 0
    Prodigy 40 points

    Additional question: I'm aware of the recommendations in application note sboa620 regarding EMI filtering of VS, VOUT and VREF pins. But how about OC pin? We are routing it quite far away, so it picks up noise quite easily. However, the OC needs to be very fast so you have to be very careful if you put some EMI filtering there. Do you recommend adding a ferrite bead and a capacitor to OC pin as well?

  • 0 in reply to Olli Pokkinen
    TI__Mastermind 23015 points

    Olli,

    Thanks for using E2E. We exercise a test condition for the device of 3mA during test, as we show in the comparator section of the datasheet. This should be more than sufficient current for most cases (for a Vs of 5V, this would equate to an ~1.6k pull up resistor). 

    Regarding the question on EMI resilience, this pin is simply an open drain output, and as such should be resilient to EMI. We did do some testing with ferrite bead on the OC pin which demonstrated that the pin will still work in this configuration, but ultimately the pin is not very susceptible and therefore the bead was excluded from recommendations in the note. If you are concerned with the length of the trace in a very EMI heavy environment, you could also potentially look at buffering the output to help keep the integrity of the signal in this case. 

  • 0 in reply to Carolus Andrews
    Prodigy 40 points

    Hi Carolus,

    I actually noted that 3mA test condition already but we would probably need to go higher than that. Do you think 5mA or 10mA would still be ok?

  • 0 in reply to Olli Pokkinen
    TI__Mastermind 23015 points

    Olli, 

    I think 5mA would be acceptable here, but unfortunately I do not have data to back that up. Is there a reason why the large current is needed here? The OC triggers extremely fast at 3mA, so I am curious why there is need to sink such a large current here. 

  • 0 in reply to Carolus Andrews
    Prodigy 40 points

    We are connecting together the OC output from several sensors and routing the net in very high interference area, leading to lots of noise is coupled to the signal. So we need to have very low input impedance at the receiving circuitry in order to avoid false OC tripping but still maintaining the fast response in case of actual OC trip.

    If 3...5mA is the maximum you can guarantee to be safe, that is the information we have to live with then, thanks.