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UCD3138PSFBEVM-027: UCD3138PSFBEVM-027 : Firmware update support

Part Number: UCD3138PSFBEVM-027


I have been testing UCD3138PSFBEVM-027 board currently and wanted to do output voltage modifications in it. Currently the EVM is designed to provide 12V output. 

I want to bring it down to a lower value (8V or 10V). For this I did few changes in firmware (pmbus_topology: screenshot attached). But this is giving 0V output and D26 and D4 are flickering. The firmware is updated and UV level, nominal voltage and OV level are reflected in fusion studio online software.(screenshot attached). 


Kindly let me know what additional changes are required with respect to firmware.

Also ,Kindly let me know if only firmware changes are enough for bringing down the voltage or hardware changes are also required.

As per my understanding for increasing the voltage and power rating, hardware changes are required (due to transformer and many other components and current carrying path constrains). But is the same applicable for lower voltage?


  • Hello,

    Yes, the board should work with low voltage. UV is still possibly triggered because you may not change every UV setting. Please double check firmware.

  • Hello,

    Since I am not a software person, I could only find one parameter related to UV in firmware VOUT_UV_FAULT_LIMIT (in pmbus_topology.h)

    It will be really helpful if you could let me know what other parameters might affect UV in the firmware.


  • Hello,

    For test purpose, there's one simple way to see if the output voltage would change to the expected: 

    Try to change the FeCtrl0Regs.EADCDAC.bit.DAC_VALUE via memory debugger online-----that way the output voltage shall change from 12V to a lower value(say, 10V). Once this way works, try to look into the firmware and find out releated code about FeCtrl0Regs.EADCDAC.bit.DAC_VALUE.

    Best Regards,


  • Hello,

    I found FeCtrl0Regs.EADCDAC.bit.DAC_VALUE in memory debugger. The value set in there is 4080 but according to the default firmware program (sluc614) uploaded the value should have been 6080 (for 11.875V). 

    What does that 4080 represents?

    Kindly let me know if I need to make changes over the same place to get lower output voltage?


  • I think this is voltage reference you changed for 8V. It doesn't affect the UV protection.

    The below code is used by digital comparator for UVP

    FaultMuxRegs.DCOMPCTRL0.bit.THRESH =750;  you may try to change it to a lower value, such as 300.