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DRV10975: What is the I2C frequency range and load capacitance

Sourav Gupta1
Prodigy 50 points
Part Number: DRV10975

Hello,

I would like to know what is the frequency range of DRV10975? 

Also, how much load capacitance it provide over the I2C bus line?

Thanks a lot.

  • 0
    TI__Mastermind 24405 points

    Hi Sourav,

    Thanks for posting your question in MD forum. I2C frequency in DRV10975 is 400 kHz. Load capacitance is board dependent and this has to be measured on your I2C line. Pull up resistor is selected based on this capacitance to meet the rise time. Refer to this App note for more details.

    Regards,

    Vishnu

  • 0
    Prodigy 50 points

    Thanks for the reply. My planning is to having a separate driver board from the mcu board and the communication will happen through wires. I want to calculate the loading in the I2C bus line. In the separate DRV10975 board, there will be other devices on the same I2C line.

    Could you confirm how much capacitance it provides over the I2C bus line so I can calculate the maximum applicable wire length? 

    Also, is it possible to run the DRV10975 in 100Khz I2C speed?

    Thanks a lot.

  • 0 in reply to Sourav Gupta1
    TI__Mastermind 24405 points

    Hi Sourav,

    We recommend 4.7k ohms as the pull up resistance assuming that 80pF of capacitance is on the line. In other words, if the I2C speed is at 400 kHz and pull up resistor is 4.7k Ohms, then the load capacitance should be around 80 pF. 

    Unfortunately, we cannot run DRV10975 at 100 kHz I2C speed.

    Regards,

    Vishnu.   

  • 0 in reply to Vishnu Balaraj
    TI__Mastermind 24405 points

    Refer to this E2E post  for more details.

  • 0 in reply to Vishnu Balaraj
    Prodigy 50 points

    Thank you. Is there any way to know what is the capacitance of DRV10975 if run at 400kHz?

  • 0 in reply to Sourav Gupta1
    TI__Mastermind 18900 points

    Hello Sourav,

    I think the question you're asking is if there is a specification for equivalent capacitance on the SDA and SCL pins. Assuming this is the case, we do not have this specification in the datasheet. In general, we find that the capacitance of the trace is always much larger compared the DRV. As such, it is considered negligible in the calculation. If you want to include something in your calculation, you can assume for ~70 fF for the DRV, max.

    Because this problem depends board layout more specifically. Its recommended to build a board, use a sufficiently low resistor that works for unrealistic C (maybe 4.7k ohms), measure the performance of rise and fall time, and increase the resistance until you are satisfied with rise and fall time performance.

    Otherwise, use some theoretical models and figure out a way to estimate or measure C on your line (0.254-0.762pF/cm) and determine the maximum R you can put.

    In both cases, after that you must account for manufacturing variance of the DRV (i gave you max so you the performance will only get better), the bus trace, and anything else on the bus line.

    By the way, this is all outlined in the links that Vishnu provided. I suggest you thoroughly read through the theory if something doesn't make sense.

    Best,

    -Cole

  • 0 in reply to Cole Macias
    Prodigy 50 points

    Thanks a lot Vishnu and Cole. This resolve my issue.