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Original question:

BQ76PL455A-Q1: Most recommended BMS IC

BQ76PL455A-Q1: TIDA-00717 common mode chockes

Lukasz Przenioslo
Expert 2630 points
Part Number: BQ76PL455A-Q1

Hello there,

I am designing a device around the BQ76PL455A-Q1 based on the TIDA-00717 EVM board. In the communication path I have noticed some common mode chokes (T5, T6, T7 and T8):

These are quite expensive parts and I am looking for the options to reduce their usage. For instance, in the IC's datasheet we can read:

So the 1st question is: Do we really need to use the FAULTL/ FAULTH as differential pair? Since the hearbit is only 10 kHz and it does not really provide any data other than "toggling or not toggling", then maybe a simple opto isolater line would do?

In the DS we can see the following exemplary designs:

It can be noticed that the chokes are only present on the COMML/ FAULTL lines, but not on the COMMH/ FAULTH lines. This is different from the EVM, in which chokes are redundant. 

Question 2 is: is it safe to omit the chokes on 1 of the sides as presented in the DS?

I would appreciate all feedback.

  • 0
    TI__Genius 17370 points

    Hi Lukasz,

    We highly recommend including the chokes on both sides if the two devices are on separate pcbs so in most cases you would need both. The reason is to improve robustness in noisy conditions so you could evaluate based on the conditions of your system but for automotive test cases, these would be very important to reduce any risks.

    Regards,

    Taylor

  • 0 in reply to Taylor Vogt
    Expert 2630 points

    Hello, thank you for the answer.

    Is there any cable length vs noise amplitude/ frequency reference? This is aimed towards bms application, in which there will be high DC current floawing nearby through the string. Also the battery blocks should be placed next to each other, so we are talkong about cables lengts close to 30 cm or so. Also it seems that the working conditions for the communication channel is different than for the fault channel- the latter is only 10 kHz square wave, while the former is 1 MHz+, right? If so, does the fault reaquire so much filtering?

  • +1 in reply to Lukasz Przenioslo
    TI__Genius 17370 points

    Lukasz,

    We don't have a reference guide as we leave this up to customer flexibility, but because of this may require some tinkering to ensure the waveforms look okay with certain changes. It is ultimately up to you and the noise that presents itself in your system, but I recommend the chokes for best performance in general.

    Regards,

    Taylor