• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 33 subscribers
  • Views 323 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.

Original question:

P82B96: P82B96

P82B96: P82B96 does not follow I2C spec.

Warren Hawkins
Prodigy 10 points
Part Number: P82B96
Other Parts Discussed in Thread: INA260, INA228, , TIDA-01608, ISO7842, ISOW7842

Tool/software:

I've used this part (P82B96) as part of the TIDA-01608 reference design but replaced the current sensor with a INA228. The communications does not work. I've scoped the communications and found that the output of the P82B96 only gives a 0.8V low logic level which is higher than the INA228 spec in the datasheet. The Datasheet lists 0.4V or less. The original INA260 would work to 0.3*VS which I missed. I've attached the scope output and the schematic in pdf and screen capture form. The purple on the scope is the isolated ground of the INA228 and P82B96. The yellow is SCL and green/blue is SDA. The INA228 is not acknowledging receipt of the packet. I've verified the address etc. I assume the reference design worked with the higher VIL of the INA260 but the question is how can I make this work without a board spin?

PC1F100701P-02.pdf

  • 0
    TI__Mastermind 48608 points

    Hi Warren,

    The P82B96 has a high VOL on Sx/Sy pins. This offset voltage cannot be changed and is built into its design. 

    At this point, what do you need to evaluate? Do you need to check the functionality of P82B96 or would removing this device be okay? I am thinking if P82B96 is not needed, is it possible to blue wire / short across each P82B96 to removed the buffered offset voltage? 

    I think the ISO7842 device VOL would be within range for the INA228. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 10 points

    Do you mean short from Ry to Sy? Will there be any feedback issues doing this?

  • 0 in reply to Warren Hawkins
    TI__Mastermind 48608 points

    Hi Warren,

    I was thinking something like this: 

    But I am not sure that the ISOW7842 can short an OUT to IN pin. This is why I was asking about what devices you need to evaluate. IF its only the INA228 that is in evaluation, you could remove the P82's and the ISO device and short across the buffers / Iso barrier to communicate directly with the INA228. 

    P82B96 most likely needs to be removed. I don't have a certain answer for how to handle the bi-directionality of SDA across the ISO device. This is all to keep the VOL's low enough for the INA228 to work. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 10 points

    I left the P82B96 connecting to the STM32 as it can work with those levels. I removed the one between the INA228 and the ISOW7842 shorted the connection for the in on the ISO to INA but connected the out on the ISO to the short using a Schottky diode with Cathode to the out pin.