• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 202 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.

TPS552892-Q1: Pulse operation in PFM mode

Arvin Zhang
Prodigy 20 points
Part Number: TPS552892-Q1

Hi team,

I tested some waveforms in PFM mode. For the pulse operation at switching times, I have few questions:

1. At buck, boost and buck-boost mode, the switching pulse seems to use the same period operation as PWM mode. Why don't use a long period logic to make IL and Vout increase continuously and quickly?

2. For now PFM mode, the switching time is about 3 periods. Is this fixed or determined by Vout?

3. In picture 2, buck mode, the first switching pulse is ringing, what's the reason?

Could you please make any comments? 

Thanks & best regards,

Arvin

               

Vin=8V, Vout=12V, Io=0A, PFM

Vin=8V, Vout=12V, Io=0A, PFM

Vin=12V, Vout=12V, Io=0A, PFM

Vin=14V, Vout=12V, Io=0A, PFM

  • 0
    TI__Mastermind 27970 points

    Hi Arvin,

    Due to bandwidth limit, I will reply to you later today. Thanks.

    BRs,

    Bryce

  • +1
    TI__Mastermind 27970 points

    Hi Arvin,

    Here are my comments.

    1. At buck, boost and buck-boost mode, the switching pulse seems to use the same period operation as PWM mode. Why don't use a long period logic to make IL and Vout increase continuously and quickly?

    -> The duty cycle is still in control, and considering the loop response time, the effect should not differ much.

    2. For now PFM mode, the switching time is about 3 periods. Is this fixed or determined by Vout?

    -> It is not fixed, and can be determined by Vin, Vout, L, Cout, loading current and compensation parameters.

    3. In picture 2, buck mode, the first switching pulse is ringing, what's the reason?

    -> When the MOSFET starts switching, it will first turn on the low side FET, and then ZCD is triggered, so the inductor is oscillating with the Cds of Buck FETs. It is normal operation waveforms.

    BRs,

    Bryce

  • 0 in reply to Bryce Xun
    TI__Prodigy 20 points

    Hi Bryce,

    Thank you for your kind comments!  I now understand the operation logic.

    BRs,

    Arvin