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BQ76940: Power management forum

Part Number: BQ76940
Other Parts Discussed in Thread: ISO1541, BQ76PL455A-Q1

Good Day

For the 48V battery, I have designed the battery monitoring system using 15 cells and based on the BQ76940 chip.

Now, I would like to stack them up in order to monitor the 400V system. I just wonder whether it can be achievable using ISO1541 I2C isolators. I do not require to charge and discharge MOSFETs and current measurements, so there is no reference to the ground. The voltage monitoring and balancing functionality are only required. 

  • Hello Dmitriy,

    You should be able to use the I2C isolator to communicate with all of the devices. Check their product page or forums to see if there is any other considerations to take. I believe you could do it with the ISO1541 with no issues.

    400-V seems rather high. For that high voltage, you would have to stack many ICs. Even though stacking for these voltages may work if proper cell connection order is done, we usually suggest to stack up-to 2 ICs. It is very easy to break stacked ICs.

    I would recommend you look into our automotive-rated ICs, like the BQ76PL455A-Q1. These are made with stacking in mind and can easily be daisy-chained.

    Best Regards,

    Luis Hernandez Salomon

  • Hi 

    my idea is that each two BQ76940 (96V) will be communicating to the host via 2 I2C isolators, the next two including isolators will be referenced to the top of the first two and so on. So the last two will have 300-400V in relation to the host.

    Do you think the I2C isolator is capable of withstanding that working voltage? Sorry, if I am repeating the question.

    Also would you please confirm the availability status of the BQ79600, BQ79616 parts? 

  • Hello Dmitriy,

    The I2C isolators are part of another product line and has their own set of engineers supporting it. You may have to open a thread to make sure that you can use the isolators in your application at those voltages.

    I apologize, I don't know when these would be available. Those two parts are also part of the automotive-rated monitors, so they have a different team working on them. We are experiencing IC shortages in many areas, and there is no estimated time for when the parts will be in stock.

    You may have to open another thread to confirm availability.

    Best Regards,

    Luis Hernandez Salomon