• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 132 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LMZ31710: External Clock in Parallel operation

Hue Phung
Prodigy 140 points
Part Number: LMZ31710

Hello,

I have a question regards the external clock in parallel operation with two LMZ31710 deivces. According to the Application Report  SNVA695  "The clock must be present before input power is applied", but in my case I don't have a clock unless this switcher runs and generate the low voltage rail. So the question is what happens  if I apply the clock after the parts are running? I intend to apply external clock only to the master and let the slave run off the Sync_Out of the master.

In my previous design which uses only one LMZ31710, I also apply the clock after the part runs up and generates the voltage rail which powers the clock circuit and it seems to run fine, I have to mention that I apply the clock through an AC coupling circuit.

Thanks in advance!

  • 0
    TI__Mastermind 35115 points

    Hi Hue,

    I don't see any issue not having a clock before if the slave is running off the SYNC_OUT of the master. With the AC coupling circuit, the master device will properly set the switching frequency with the RT resistor and the SYNC_OUT clock of the master should be available for the slave before switching starts Once the clock is available, the master will synchronize to the clock and the SYNC_OUT will follow it.

    The scenario you will want to avoid is the clock going away while the parts are running. When the clock goes away, the fsw of the LMZ31710 will drop very low resulting in very high output ripple. The output ripple is often high enough that it causes PWRGD to go low.

    Anthony

  • +1
    Prodigy 140 points

    Anthony,

    Thank you  so much for confirming it

    Have a great day!

    Hue