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BQ76PL356. ISOLATED POWER SUPPLY?????

Inigo Acero
Prodigy 40 points
Other Parts Discussed in Thread: BQ76PL536, BQ76PL536A

Hello.

I want to use BQ76PL356 to monitor ultracap charges.

4 cascaded BQ to control up to 24 cells.

BQ76PL536 is able to disable protections, and I can control the charge of the suparcaps (initially discharged) usign external hardware and when supercaps get the minumum recommended voltage BQ76PL536 would begin to manage them.

Usually all related examples take the power supply for the BQ76PL536 directly from the cells. But if I manage discharged supercaps there is no  voltage to supply.

¿Can I use an external power supply?.
If so, please let me know how I need to connect the external power supplies to the four BQ76PL536 cascade connected.
I suppose I should connect isolated power for each BQ76PL536, connecting possitive to BAT and negative to VSS................... need the external power supply to be higher than the maximum voltage that could reach all the cells connected to BQ76PL536?.

Last question:
I´m not able to see clear differences between BQ76PL536 and BQ76PL536A.
Is the accuracy the main advantage of the BQ76PL536A?. Or............ are there other interesting advantages to take care about?.
I´m not sure if I should push BQ76PL536A instead of BQ76PL536.

thabks and regards

  • 0
    TI__Genius 10785 points

    Yes, you can use external power supplies to power PL536. You need to connected isolated power for each IC just like you mentioned. Your idea of setting external power supply to the max voltage will work as well. 

      We have released Q1 version of PL536. Q1 version will have better accuracy.

    Main difference between PL536 and PL536A is selectable CRC reporting. You can disable CRC reporting with PL536A IC.

    Please contact me directly for more details.

  • 0 in reply to Roger Hwang
    Prodigy 40 points
    I'm designing monitoring board with two BQ76PL536A (12 cells). I also want to use external isolated supply. Is there any reference schematic or appnote with such design available?

    I have few questions:
    Is the change in input resistance of VCn inputs possible when board is not powered and cell voltages are present on VCn inputs?

    Will external supply affect the vertical interface performance, or is there any max voltage of which Vsupply can exceed top cell voltage of each BQ?

    North vertical interface pins of higher BQ should be connected to top of stack or Vsupply?

    Regards
    MS
  • 0 in reply to Marek Sanaluta
    TI__Genius 10785 points

    HI MS,

    I don't have reference schematic for external circuit. Every customer that I know uses cell to power the pl536A.

    Let me answer your questions 1st.

    1. No, you don't change the RC filter. You will have same RC filter.

    2. I don't see how you will do daisy-chain with external powers because Vbat of bottom IC should be same potential with GND of upper IC. I recommend you to do multi-drop configuration. check out TIDA-00821 for your reference.

    3. Check the TIDA-00821 for reference. Yes, _N pins of north(top) IC must connect to Vbat of north IC. _S pins should be connect to GND.

    Things to consider for your design.

    1. External PS to VBAT must be greater than Vc6. So, you can apply(example) 20V to Vbat and cell voltage can be 3V each. Never to have Vbat voltage lower than Vc6. YOu will lock up the device.

    2. I don't see how you can do daisy chain. Do mutli-drop config.

    May I ask why you want to use external power supply?

  • 0 in reply to Roger Hwang
    Prodigy 40 points

    Thank you for your answer.


    We wanted to avoid situation when measuring board cannot be powered because cells are completely drained (we also use LTO chemistry), but at the end we decided to use reference design.