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Original question:

BOOSTXL-TPS650861: Buck3 and Buck5

BOOSTXL-TPS650861: TPS650861:step size issue for BUCK3,4,5

Ashish Kumar Pandey
Prodigy 115 points
Part Number: BOOSTXL-TPS650861
Other Parts Discussed in Thread: TPS650861

Tool/software:

Hi,

We are using TPS650861 in our design.

By default BUCK3,4,5 step size should be 25mV as per datasheet but the output voltages correspond to 10mV step size.

Kindly help with this .Is there any to modify step sizes of BUCK3,4,5.

Regards,

Ashish Kumar Pandey

C-DOT Delhi

  • 0
    TI__Guru* 80963 points

    Hi Ashish,

    You are correct that Bucks 3,4,5 do not have programmable step size, so it should not be possible to have 10mV step size. Perhaps there could be a different issue influencing the results you are measuring. Are you using an EVM or a new board?

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 115 points

    Hi Matt,

    We are using a new board (schematic attached).Also I2C dumps for 0x5E and 0x38 as well as OTP generator tool has been attached for your reference.

    Only BUCKs viz. 1,2,3,4,5,6 have been used to supply power .No LDOs and SWs are required.

    The values  in OTP_extra addresses.jpg weren't burnt as the description of the address can't be found in the datasheet. These values are generated by OTP generator tool.

    Please help with this.

    Regards,

    Ashish

    2548.TPS65086100 OTP Generator V2p5.xlsx

    tps650861-TI.pdf

  • 0 in reply to Ashish Kumar Pandey
    TI__Genius 10772 points

    Hi Ashish,

    Thanks for this information. I am looking into this to try and provide a response. I may have more follow up questions, but need to dig deeper first.

    Thanks,
    Field

  • 0 in reply to Field Tolson
    TI__Genius 10772 points

    Hi Ashish,

    Based on your above image, these values seem to align with what you are asking for in your OTP generator and a 25mV step size:

    0x40 = 1.2V, 0x28 = 0.9V, 0x70 = 1.8V.

    These values technically result in a modulo of 0 when using 0.025 and 0.01, but this would be expected.

    • Can you please provide me what values you are seeing on these rails and an oscilloscope capturing this?
    • Can you let me know where you are testing for these values? It may be possible that the pin is outputting this value and there could be some losses downstream. Perhaps similar to something like Matt is suggesting.
    • Are you able to access the GUI and read back the registers while utilizing the device?
    • Are you drawing a load? 

    Thanks,
    Field

  • 0 in reply to Field Tolson
    Prodigy 115 points

    Hi Field,

    We tried re-programming the device on another OTP bank and it works fine this time.The output voltages are as per the set step sizes of  the respective bucks.

    This time we also burnt the values given in OTP_extra addresses.jpg.

    Kindly help with the meaning of values given in OTP_extra addresses.jpg.

    Regards,

    Ashish

  • 0 in reply to Ashish Kumar Pandey
    TI__Genius 10772 points

    Hi Ashish,

    That is good to hear. 

    Ashish Kumar Pandey said:
    Kindly help with the meaning of values given in OTP_extra addresses.jpg

    I believe you are referring to the items labeled with 38 in your picture above? 

    This would have to deal with the programming registers whose i2c address is 0x38. You can see this information, the registers and other information regarding these, in section 5.12 on page 83 of the datasheet linked here. The additional registers are reserved registers and should only be changed by the OTP Generator and not by hand. 

    Thanks,
    Field