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Original question:

BQ25750EVM: Switch time from VIN to Battery for VSYS Power

BQ25750EVM: Switching time from VIN to BAT at VSYS

Jock Duncan
Prodigy 60 points
Part Number: BQ25750EVM
Other Parts Discussed in Thread: BQ25750

Tool/software:

A thread was already created about this, however the final response in that thread was;

"Hi, we are using some experimental settings to achieve the results I shared with you. These settings are not final yet and cannot be modified by the user. These settings are set at the factory."

My question is - are these settings finalised yet? When it is said that these are experimental and cannot be changed by the user - does that mean we are stuck with the 1.3s switching time indefinitely? Would that mean that if I buy an EVM, it doesn't have these experimental, factory configured settings?

The purpose behind this question is that I am considering this device for use in a low voltage UPS system. Typical UPS switch over times are in the the single digit millisecond range. Obviously, 1.3s is far too long, and thus would make this device unsuitable for such an application."

My other question, is the switching time between switching VSYS to BAT directly, as opposed to switching VSYS via the reverse mode - i.e. using the buck-boost supply in reverse mode.

Thanks

  • +1
    TI__Mastermind 19370 points

    Hello Jock,

    Thanks for being patient with the wait. The person who normally answers these types of questions is on TBK. 

    We are not changing the bit settings of the BQ25750 at the moment.

    By the way, where are you seeing the switching time is 1.3s? I've worked with the power path switchover in the lab and the change is far faster than 1.3s. With auto reverse mode, it takes around 50µs for the converter to start working in reverse and provide power to SYS.

    I will get to you back to tomorrow about the actual change over time from VIN to BAT at SYS.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 60 points

    Hi Ethan,

    Thanks for the response. Actually, I haven't obtained an EVM kit or done any measurements, the 1.3s is what another user reported measuring and stated in the other thread. 

    50us for auto reverse mode sounds great; for my application this is potentially the mode I would actually prefer to use rather than running SYS from BAT directly, as I would like to maintain a regulated SYS supply at all times from either AC or BAT. I was assuming this would be slower than the VIN to BAT switchover time to SYS, but perhaps that isn't the case.

    Thanks
    Jock

  • 0 in reply to Jock Duncan
    TI__Mastermind 19370 points

    Hello Jock,

    Thanks for the clarification. Yes, the charger responds pretty quickly after VAC is removed.

    If you start testing with the EVM or the IC, you'll probably need to adjust the under-voltage threshold, over-voltage thresholds, and the battery charge voltage. You can refer to the BQ2575X design calculator on how to do this: https://www.ti.com/tool/download/BQ25756-DESIGN-CALC/

    Let me know if you got any other questions.

    Best Regards,
    Ethan Galloway