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LMZ22003 Sync Frequency Limits

Ryan May
Genius 13700 points
Other Parts Discussed in Thread: LMZ22003, LMZ22008

Hello,

I am working with a design that is migrating from the LMZ22008 to the LMZ22003. The issue is that the LMZ22008 was capable of running at lower frequencies down to 350kHz which made using a 500kHz sync signal a viable design choice.

However the move to the LMZ22003 with its minimum sync frequency of 650kHz I wanted to check if supplying a 500kHz sync signal would cause instability by not being within the designed range or if there is a potential that the converter will shut off in the case a longer duty cycle pulse at 500kHz based on the discussion on the bottom of Pg. 19 of the datasheet.

Thank you for your help.

Ryan May

  • 0
    TI__Mastermind 19070 points

    Hello Ryan, 

    I will forward this to the Apps engineer on this part to get his opinion. But anyway, I would advise against synchronizing below the 650kHz range. A couple of possible issues I can think of are larger ripple (remember the inductor is fixed inside) and possible stability concerns. 

    Regards, 
    Denislav 

  • 0
    TI__Genius 10095 points

    Hi Ryan,

    Although you can sync the part there I can't officially recommend it because it is outside the datasheet specifications.

    Here are a couple issues that can occur.  

    1) Increased current ripple, can cause the part to hit current limit early.  This will limit the load current

    2) The half frequency switching pole will cause the phase margin to decrease.  More capacitance will be needed to lower the crossover frequency.  

    Regards,

    Marc