• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 65 subscribers
  • Views 642 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS54386 problem of stability with low load

Christophe Guillon
Prodigy 60 points
Other Parts Discussed in Thread: TPS54386

Hello,

I am using a TPS54386 for generated a 15V/3,75W and 5V/8,5W based on 24V. 

I have some problem of stability when the 15V are less than 1W of load...

Have you some idea or methode to improve the converter to function in the full scale load : ~0W to 3,75W ?

Thank your help.

Christophe.

  • 0
    TI__Guru**** 191445 points

    Can you post your schematic?  What makes you think you have a stability issue?  Can you post sme waveforms that show your problem?  Do you have a measured loop efficiency plot for your design?

  • 0
    Genius 3295 points

    Going to light load can cause stability issues depending on whether or not you are in discontinuous mode. The TPS54396 uses an internally compensated current sensing scheme. It has a preset modulator gain, therefore you have to select an LC filter based on your applications ripple current and the gain plots provided in the data sheet.

    From the data sheet: "The loop response curve selected to compensate the loop is based on the duty cycle of the application and the ripple current in the inductor."

    If you reduce the load on a non-synchronous buck, you may go into discontinuous mode and your ripple current will decrease and may therefore cause an instability. More than likely your converter is going into pulse skipping mode, or a stable limit cycle oscillation. The ripple voltage does increase, but your converter is stable.

    The data sheet covers this issue thoroughly on page 24 under light load operation.

    Figure 33 shows the pulse skipping oscillations and the inductor current in discontinuous mode.

    If this is the problem, you can increase the value of your output inductor so that you stay in continuous conduction mode and the ripple current does not change. Alternatively you can increase the output capacitance.

    V/r,

    Chuck Sampson