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BQ25758: Test and measurement use case, limiting inrush current.

Eli Brantingham
Prodigy 60 points
Part Number: BQ25758
Other Parts Discussed in Thread: BQ25756, BQ25756EVM, ,

Tool/software:

I have two BQ25756EVMs and have been looking into a T&M use case with one acting as a CV source and the other as a CC sink, replacing an active electronic load/linear FETs.  I originally wanted to use them for automotive USB hub testing, but the lack of isolation on the sink side made it difficult.  We were looking into using them to test automotive electronic modules/fuse boxes, where we are expanding from 12-14V to 24V/48V architectures.  Something like the diagram below.

A couple questions:

1. BQ25768 is the right replacement for the BQ25756, correct?  We don't need the specific battery features, we just want to use the CV source (REV mode) and CC sink (Charge mode).  These would replace the current power supply and active electronic load setup.  

2. Can you suggest a high side switch/FET combo that can limit inrush current.  The DUT itself may have high side load switch controllers and with the BQ25756EVM, the VIN capacitors tripped the hard short limit, even with the EVM in HiZ mode.  Ideally, we would have a load switch between the DUT and the CC BQ that would allow the capacitors to charge while the BQ was in HiZ mode and then once charged we could start the CC BQ. 

3.  Is there a reference design for a higher current design, 20-50A or so.  This would be a T&M use case, so cost isn't as concerning.  

Thanks, 

Eli

  • +1
    TI__Mastermind 30915 points

    Hello Eli,

    Thanks for working with this.

    1. Yes, the BQ25758 is the right replacement for the BQ25756 if you are looking for a DC-DC converter.

    2. Could you lower the inrush current of the DUT by setting IOUT register of the CV BQ25758 low to begin with? For the high side switch controller, I'd recommend the TPS4800. To limit the inrush current, I recommend using an RC filter to slow down the high side FET turn ON time.

    3. Could you use multiple BQ25758s in parallel? The ICs will work in parallel in CC mode just fine. The ICs will work in parallel in CV mode fine, but the current will not be equally shared at low power levels. Also, I recommend using an external gate drive when the BQ25758's output current is above 7A.

    Let me know if these suggestions will work for you. Let me know if you have any other questions.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 60 points

    Ethan,

    Thanks for the detailed reply.

    I think I'll try out the TPS4811 with its pre charge FET, as well as its RC limiting capabilities.  Some of these DUTs are a distribution boxes, one input, many outputs, so it's better to try to limit the inrush on the load side.  I'll order a couple evaluation boards and move forward with the design, thanks.

    -Eli