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LM3488 External clock generation @ 550 kHz

HUGUES MARCEAU
Prodigy 170 points
Other Parts Discussed in Thread: LM3488, PMP11112, CD4017B

Dear TI community,

From a single DC bus, I want to generate 2 outputs using two boost converters using the LM3488 controller, both at 550 kHz.

- Should I synchronise their switching?
- If so, how should I generate the external clock signal? Obviously, the cheapest solution, the better. Schmidt trigger, 555 oscillator, Pierce oscillator, or ... ?

Thanks, and regards,

Hugues

  • 0
    TI__Guru**** 191445 points

    Please put the part number in your post title.  That way it will be directed to the proper support person...

    2) Start the Subject line with the part number, followed by a short description of what the post is about.  This helps the other members in the forum understand the basic content of your question or problem.  The part number is important because it increases the probability that someone who has worked with that specific IC will see your post and be able to assist.

  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points
    I'll do it for you this time...
  • 0 in reply to HUGUES MARCEAU
    TI__Guru**** 191445 points
    You are welcome...
  • 0
    TI__Expert 6860 points

    Hi Hugues ,

    Is EMI a concern for your application ? Synchronization will be helpful in avoiding beat frequency .Further out of phase clocks would be helpful particularly in reducing MW band harmonics .

    You may use 555 based timer circuits as used in TI design PMP11112 http://www.ti.com/tool/PMP11112 .

    ---Ambreesh

  • 0 in reply to Ambreesh Tripathi
    Prodigy 170 points

    Hi Ambreesh,

    It helps. Thanks you.

    Yes. I want to minimize EMI: enough to pass certifications. I sadly haven't understood you: would it be easier to control EMI if I synchronize the two clocks or not? Webench optimized for me two DCDC designs at 550 kHz. Are you saying that it would be preferable to use a 1.1 MHz clock and to have them to switch in phase, separated by 180 degrees using the CD4017B?

    Thanks, again!

  • 0 in reply to HUGUES MARCEAU
    TI__Expert 6860 points

    Hi Hugues,

    For minimizing EMI , you can SYNC two Boost circuits with 550KHz out of phase clock (180 degree) .

    The clock can be generated either through 555 timer + counter combination ( 1.1Mhz 555 output can be divided down to 2 using reset signal and out of phase clocks can be generated ),  555 timer + inverter , schmidt trigger or positive feedback opamp +  inverter etc

    ---Ambreesh