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TPS53681: TPS53681+CSD95490Q5MC 6 phase design, why i cannot see Iout values from Ti Fusion power designer.

Part Number: TPS53681

I have 6 phase design with components mentioned. Design seems to work ok (as we are in bringup phase), i can take 150A load (0.85V).

Telemetry works for input current/voltage, output voltage temperatures, but i dont have any values for output current in telemetry. 

My output inductors are PA4390.121HLT  ... 

What to test, what to change?

  • Hi Janne, Can you please provide some more details:

    - Version of Fusion GUI (try updating from here: https://www.ti.com/tool/FUSION_DIGITAL_POWER_DESIGNER

    - Screenshot of behavior from Fusion or Reading procedure in your side

    - Configuration file

    - Snip of schematic containing the controller + power stage

  • Hi Matt,

    Updated to latest fusion, no change.
    snapshot of telemetry window

    TPS53681 @ PMBus Address 88d Project.xml

    xml file of current setup

    Schmatic of this particular power. 

  • Hello, Can you measure the voltage on the individual CSP, TSNS and VREF pins? I am not able to view the schematic clearly because the image quality is poor. 

  • core_switcher.pdf

    Hi Matt, 

    Please find attached .pdf of schematics, this should be readable. 

  • Hi Matt, 
    It seems that this problem is only in one of our cards. I need to figure out why. But otherwise this power works (at least it seems to). 
    Is current measurement used for control loop feedback?

    Best Regards

    Janne Panu  


  • Yes, the TPS53681 does use the CSP information for control loop feedback (it is a valley current mode controller). Actually without any current feedback, the loop would probably be unstable.

    Can you please measure the voltages on the CSP/VREF/TAO pins? You should see the CSP pins sitting at about 1.7V for 0A. The TPS53681 will not report negative current, so if it is much lower, we would not know from the GUI alone. This could indicate an issue on the power stage side, or with assembly, or with the bypass caps for VREF etc... 

    I did not see any obvious issues in the schematic which could lead to this. But if it is only 1 board/many this makes sense. 

  • 6254.non-working.zip8321.working.zip

    Hi Matt, 

    Please find attached zip packets of measurements. 
    Since our layout is very tight, i cannot measure with proper ground spring probe, so lots of interference (only exception is vref measurement of working one, this i could measure with power probe and very short ground loop). 

    So 1 not working card, 2 working cards so far (as in current measurement in gui). Even the not working makes correct voltage, is stable, and i can load it with 150amps. 

    Calibrations for input and output currents are not done, so measurement accuracy is not good. 

    U6500 is the top output stage, and U6505 is the bottom one. 

    Temperature measurement seem to work on "not working" unit. it gives temperatures that seems valid. 

    Non working i measured those close to output stage, working ones i measured close to controller. 

  • Can you just try to look at the DC value with a DVM? The waveforms are really distorted. I also suggest to take a look at the board soldering and assembly quality since it’s only one which is not reporting correctly

  • HI Matt

    working unit with 20A additional load (approx 25A total)

    Vref: 1.698V all FET
    TS_fet:0.960V all FET
    TS_ic:0.960V
    Isen:1.711V all FET

    These makes sense to me, seems valid

    non correctly working unit 20A total
    Vref:
    U6500:1.699
    U6501:1.699
    U6502:1.698
    U6503:1.948
    U6504:1.699
    U6505:1.699
    TS_fet:
    U6500:0.974
    U6501:0.977
    U6502:0.976
    U6503:0.977
    U6504:0.977
    U6505:0.978
    TS_ic:0.979
    Isen:
    U6500:1.487
    U6501:1.674
    U6502:1.274
    U6503:1.455
    U6504:1.675
    U6505:1.385

    Tsen seems to be valid (and GUI shows valid values). 

    Isen is not ok, 

    U6503 Vref is not ok 

    I am planning to have control IC and FETs replaced on this problematic unit

  • I agree, these voltages do not make sense. I suggest to replace the power stages and controller one-by-one if possible. It is a little strange that they are all incorrect. Also, double check the bypass capacitors and board connections. 

    U6500:1.487
    U6501:1.674
    U6502:1.274
    U6503:1.455
    U6504:1.675
    U6505:1.385

  • Now control ic and all fets are changed

    Now current measurements seems to work, and Isen seems valid, but phase5 shows (and voltage is) way too high compared to others. (other phases shows 2A, and phase 5 shows 10A, when i have around 14A load). So debugging continues. 

  • Thanks for the update.