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BQ25895: Design query

Saurabh Sinha
Prodigy 20 points
Part Number: BQ25895
Other Parts Discussed in Thread: TPS566238,

Tool/software:

Q1. Can I get 3.3V from the VSYS pin to power my board? If not, can I use TPS566238 (at VSYS) to get 3.3V, 2A? Any other better suggestions to replace TPS566238.

Q2. Is it safe to copy the layout design of BQ25895EVM completely?

Q3. I have two adapters, A1 can provide 5V/3A, 9V/3A, 12V/3A, 15V/3A. But, A2 can provide 15V/3A only. Considering the recommended limit of 14V on VBUS, if I put a 130-ohm ILIM resistor for a 3A input limit then what voltages will I get if I use A1 and A2?

  • +1
    TI__Genius 16425 points

    Hi,

    Saurabh Sinha said:
    Q1. Can I get 3.3V from the VSYS pin to power my board? If not, can I use TPS566238 (at VSYS) to get 3.3V, 2A? Any other better suggestions to replace TPS566238.

    The SYS voltage is likely to vary based on the presence of a VIN and your battery voltage, though you can configure a SYSMIN voltage of 3.3V. A discrete Buck can be used in this scenario to get 3.3V, the TPS566238 can work though there are many options for discrete bucks. I recommend creating an E2E thread with a buck part number to check directly with the buck team on the most suitable device for your application.

    Saurabh Sinha said:
    Q2. Is it safe to copy the layout design of BQ25895EVM completely?

    Yes, this is fine.

    Saurabh Sinha said:
    Q3. I have two adapters, A1 can provide 5V/3A, 9V/3A, 12V/3A, 15V/3A. But, A2 can provide 15V/3A only. Considering the recommended limit of 14V on VBUS, if I put a 130-ohm ILIM resistor for a 3A input limit then what voltages will I get if I use A1 and A2?

     The device has an input overvoltage threshold of 14 - 14.6V. This means that applying DC voltage greater than 14V the device will not be able to pull any current from that input. The ILIM resistor with a higher input limit only has an impact on the maximum current that can be pulled from a source, so the voltages if you use A1 will depend on how your input source responds to different current loads. In this case, your inputs greater than 14V will not be usable by the device.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 20 points

    As you said, "SYS voltage is likely to vary based on the presence of a VIN and your battery voltage." Should I hook up my Buck's Vin with BQ25895 PMID pin?

  • 0 in reply to Saurabh Sinha
    TI__Genius 16425 points

    Hi,

    SYS and PMID can both vary based on VIN or VBAT. PMID can be boosted back up to 5V when using OTG mode. Your BUCK VIN can be connected to PMID or to SYS.

    Best Regards,

    Juan Ospina