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TPS53667: operation inquiry

Renan Santos Adriano
Genius 17350 points
Part Number: TPS53667

Hello team,

I'm posting this inquiry on behalf of my customer, please see details below.

Using your development tool I’ve made power supply system (power net.pdf), with little adjustments (for supply_1 vout changed and added 6th phase) applied it in design. Resulting design for supply_1 is in P9_RB.pdf.

I’ve got several questions about TPS53667 operation:

  1. How load line setting is working? I changed this parameter from 1 mOhm to 0 and to 2 mOhm, applied and released 30A load, but Fluke multimeter’s readings under load (not near power supply, but exactly where load is situated) did not change. Why or what I don’t understand? What should I expect when I change this value?
  2. Using https://www.ti.com/lit/ug/slvu719b/slvu719b.pdf?ts=1638444709036&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS53819A and figure 4-1 technique I’ve made oscillograms when I applied 30A load (LeCroy.png) and released load (LeCroy1.png). According oscilloscope more load results in more Vout (constant level is up to 70mV higher), but Fluke shows what it don’t happen. What do I do wrong?

Attachment.zip

 Regards,

Renan

  • 0
    TI__Intellectual 795 points

    Hi Renan,

    When load line is enabled, the output voltage regulation level drops with the increase in load as shown in the figure below (figure.9 from the TPS53667 datasheet. Higher the load-line, lower the output voltage for a given load.  When load-line is 0mOhm, output voltage regulation level does not change with load.

    So, when you measure the output voltage at 30A load with load-line =0,1, and 2mOhm, you should get the lowest output voltage measurement  with load-line=2mOhm  and the highest output voltage with load-line =0mOhm and in-between these two when load-line =1 mOhm.

    It looks like the scope shot "Lecroy 1" corresponds to the load increase case as the output voltage is dropping after the load has been applied. From this scope shot, the load-line is 1.67mOhm (=change in output voltage/change in load=50mV/30A).

  • 0
    Prodigy 90 points

    Good Day!

    Thank you for answer. I still have some questions. I changed load line and nothing happed. Multimeter (I trust it more then oscilloscope) showed no difference under 30A load between 0 load line (set by resister or 0% in register via fusion design) and 1 mOhm load line. What should I check to see a difference?

    Lecroy1 is the release load. I'm sure about it because different people observe the same result on this design. They used differencial method amd probe. Maybe it's something with ground potential and it locally goes below 0V?

  • 0 in reply to Vadim Lazarev2
    TI__Intellectual 795 points

    Hi Vadim,

    Can you calibrate the DMM as mentioned below and redo the measurement?.

    Calibration procedure: Connect the DMM to 0.9V supply and record the DMM reading. Then, increase the supply voltage by 30mV (=0.930V),measure it with the DMM and record it. Now check if the DMM is 0.93V or not (or check if the DMM reading has increased by 30mV or not compared the first reading).

    Regarding the scope shot, could you capture the load current plot and output voltage plot using the "Monitor" page of the GUI (this can be find at bottom left corner of the GUI) which is shown on left side below? Also, select the VOUT and IOUT plots to plot as shown on the right side below.

        

  • 0
    Prodigy 90 points

    Good day!

    This is what I have for board with 20A load change.

    Best regards, Vadim.

  • 0 in reply to Vadim Lazarev2
    TI__Intellectual 795 points

    Hi Vadim,

    have you forgot the attachment?

  • 0
    Prodigy 90 points

    Good day!

    Due to some technical issues I was unable to answer.

    First. I cant attach docs or pics here. Can write only.

    Second. I managed to resolve issues related with load line settings. It appeared that by default ic is set to zero-load-line and external resistor had no effect (didnt find any mention about it in datasheet). Change that setting through pmbus help to observe output voltage drop under load. So, this question is resolved.

    Third. I still have no ideas about why LeCroy showed output voltage increasing under load with zero-load-line setting.

    Best regards, Vadim.

  • 0 in reply to Vadim Lazarev2
    TI__Intellectual 795 points

    Hi Vadim,

    Regarding attachments, don't you see any options to attach?

    You are seeing zero load-line because of the resistors that were used at SLEW-MODE pin.Please refer to the page#4 and #11 of the datasheet (shown below). The voltage at SLEW-MODE pin for the selected resistors sets the b[3]=1 which implies zero load line.

    Regarding the third point, having a scope-shot/a plot from GUI  (using the GUI Monitor page) showing output voltage along with load current information would be useful to comment on.