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TPS546D24AEVM: EVM Questions

Part Number: TPS546D24AEVM
Other Parts Discussed in Thread: TPS546B24A, TPS546A24A

Dear TI,

     Here are some questions I came up with while working with the TPS546D24AEVM.  Thank you for answering.

  • The default value for VIN_OV_FAULT_LIMIT is 0015 (verbatim) in the datasheet. It is 21 V in the Fusion tool. Is this correct?

  • The register PGOOD_CONFIG (0xE3) appears in the Fusion tool, but I can't find it in the datasheet (November 2020). Does this register exist?

  • If we're using an external +5 V power source for AVIN, do we keep POWER_STAGE_CONFIG at 4.7 V, or set it to 5.1 V?

  • I'm having difficulty understanding whether to use absolute or relative data format.

  • Do you have a Design Calculations Spreadsheet prepared for the EVM?

                                                                                                   -Kirk

  • Hi Kirk,

    Our expert Peter will check then reply you soon.

  • The default value for VIN_OV_FAULT_LIMIT is 0015 (verbatim) in the datasheet. It is 21 V in the Fusion tool. Is this correct?

    Yes. VIN_OV_FAULT_LIMIT uses the SLINEAR11 format, where the 5 MSB bits represent an exponent in 2s compliment format from -16 to 15 and the 11 LSB bits represent a mantissa from -1024 to 1023 and the analog value is Mantissa x 2^(Exponent)

    0015h is Exponent = 0 and Mantissa = 21 (16 + 5) 

    The register PGOOD_CONFIG (0xE3) appears in the Fusion tool, but I can't find it in the datasheet (November 2020). Does this register exist?

    Yes, you can find the detailed description in the TPS546B24A or TPS546A24A datasheet.  Despite some bits being listed as Read Only, all 16 bits are writable and have NVM backup.

    If we're using an external +5 V power source for AVIN, do we keep POWER_STAGE_CONFIG at 4.7 V, or set it to 5.1 V?

    If powering AVIN from 5V, you can connect AVIN and VDD5 to 5V to eliminate the drop-out of the linear regulator and improve efficiency.  With AVIN = 5V and the internal LDO active, there will be very little difference in performance between 4.7V or 5.1V due to the forward drop of the linear regulator.

    I'm having difficulty understanding whether to use absolute or relative data format.

    By default, the TPS546x24A family use Relative data formatting for entering OV, UV Fault and Warning Limits, and Margin High and Low.  In relative mode, these commands have the same command value irrespective of the programmed output voltage.

    In absolute mode, the command values for these commands are entered or read-back as direct voltages, and would have different values for each output voltage.

    Most users working with new programming software or firmware, find relative easier to work with as it typically requires less adjustments, but absolute mode is more common in legacy software and firmware developed for earlier versions of PMBus that did not include relative formating.

    Do you have a Design Calculations Spreadsheet prepared for the EVM?

    I do not see one prepared, but it should be noted that loop bandwidth of the EVM is somewhat limited by high layout parasitic inductance due to the linear layout of the output capacitors.

  • Kirk,

    Very glad we were able to resolve your issues for you.  If you have any further questions, please create a new thread.