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LM5149: LM5149 with adjustable output voltage with DAC8564

Godziller
Prodigy 90 points
Part Number: LM5149
Other Parts Discussed in Thread: DAC8564

Tool/software:

Good morning, I'm using the LM5149 on my design of a variable output buck converter with the following specs:

VIN = 54V
VOUT = 0.8V - 50V
IOUT = 15A (or 30A with dual-phase)

The output voltage is controlled from a DAC8564 using a PID algorithm to enable costant current or costant voltage operation.
In the early development stage I noticed that a too steep change in the DAC voltage cause a failure in both controller and mosfets.
In the firmware I limited the DAC value change to 320 every 20ms.

Now after many months of testing a few power supplies keep dying on the same death, controller + both mosfets.

This is the schematic:



How can i troubleshoot this kind of failure? What should i check first?

  • +1
    TI__Mastermind 30460 points

    Hello,

    I would make sure that your inductor value is adequately sized for output voltages >27V.  if it is not, it can cause instability.  You can check stability by slowly adjusting output voltage to prevent damage and ensure that the switch node is stable as the output voltage is adjusted.  if this is true, then I would go back to your original test slewing the output fast and check inductor current as the output voltage is changed.  I suspect the issue is occurring when you slew the output voltage down?  Are you running in Diode emulation?  if not, suggest you try as it may prevent damage if my theory is correct.

    see calculator spreadsheet below, please fil out and send back if you would like me to check, hope this helps.

    LM5149-LM25149DESIGN-CALC Calculation tool | TI.com

    David.

  • 0 in reply to David Baba
    Prodigy 90 points

    5102.LM5149-LM25149 Quickstart Calculator_rev3.xlsmThanks for the reply. The inductor is well suited for both current and voltage, its a PM2248.153. Im doing tries with diode emulation and it seems to be working better, now the problem is that i need dual phase, and the secondary module cannot work in DCM...

    Edit:
    The secondary module can actually work in DCM, its just phase shedding that is not supported but i dont really need that feature. It now works much better and I can sweep instantly from max DAC value to min DAC value without any problem.