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TCA9617A: What's the difference between TCA9617A and TCA9617B

Nanfang Liao
Intellectual 2085 points
Part Number: TCA9617A
Other Parts Discussed in Thread: TCA9617B, , TCA9517A

Hello Team,

There are some questions from my cusotmer, please help to give your comments, thanks.

1. What's the difference between TCA9617A and TCA9617B?

2. Why we need to make sure Vcca <Vccb? can you help to give more detail explanation?

3. Below is my customer's application, you can focus on TCA9617 application, VCCA > VCCB. They also use TCA9617A and TCA9617B to do the same test, for TCA9617A, the waveform is abnormal and the communication also have some error, but for TCA9617B, the waveform looks good and the communication is also good. You can check the waveform below. Do you think the wavefroms for TCA9617A and TCA9617B are reasonable? From customer's test, it seems that this application can work, what's your comments about the application for TCA9617B?

Regards,

Nanfang.

  • 0
    TI__Mastermind 23406 points

    Hello Nanfang,

    1. The main difference between the TCA9617A and B is that they B version has power off high-impedance I2C bus feature.

    2. This is a hard requirement of the TCA9617A/B architecture. It is needed as a function of the overhead of the device.

    3. I am not sure what is happening during the transactions as seen in your post, but it is likely that it is an overhead issue.

    I may have a solution for you depending on the speed your customer is trying to achieve. The TCA9517A does not have the Vcca<Vccb requirement, but it cannot support more than 400 kHz.  I saw you guys were using 100 kHz (at least that was what I could figure out from fuzzy waveforms).  It is also pin to pin compatible. 

    Why are they using two buffers in series? They could have easily did this in parallel and wouldn’t have had this issue. It also compounds delays in the system.

    I am a bit unsure of what they are trying to accomplish with this setup.  They could potentially also use this configuration but it would require new layout and more system analysis.

    Do they hare a large capacitive load?  What frequency are they running at?  Let me know.

    -Francis Houde

  • 0 in reply to fhoude
    TI__Intellectual 2085 points
    Hello

    Thanks, for item2, can you tell me why we need to make sure Vcca <Vccb? can you give more explanation about it, you know NXP part has no this requirement.

    Regards,
    Nanfang
  • 0 in reply to Nanfang Liao
    TI__Mastermind 23406 points
    Hello Nanfang,
    The part might be able to work within a range, but the part was characterized and tested with the rule that Vcca < Vccb, therefore we can't guarantee normal operation if the part is used without adhering to the rule of Vcca < Vccb.
    -Francis Houde
  • 0 in reply to fhoude
    TI__Intellectual 2085 points
    Hello Francis,

    Thanks for your quick response. theoretically, if our part must support the rule that Vcca < Vccb? or maybe our part can support Vcca > Vccb application?

    Regards,
    Nanfang