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LMS3655-Q1: Manual Spread Spectrum via external clock < 300KHz

Martin Seeger
Expert 5371 points
Part Number: LMS3655-Q1

Dear Team,

we received a request if it was possible to do a frequency sweep with the external clock.

The customer has a requirement only allowing a DC/DC switching frequency lower than 300KHz. This frequency is only possible if the device is running with an external clock. However the device will not have spread spectrum operation with the external clock.

So the idea is to have manual frequency sweep @ the SYNC pin. 

Is this possible? Do you have any information how fast the device will lock to a frequency?

Looking forward to your feedback.

Best Regards
Martin

  • 0
    TI__Expert 4100 points
    Hi Martin,
    This should be possible, but to give you a definite answer we need more details regarding operating conditions (input voltage range, output voltage, load current and mode of operation).

    Looking forward to your reply.
    Best regards
    Brani
  • 0 in reply to Brani Dubocanin
    TI__Expert 5371 points

    Hi Brani,

    thanks a lot for the answer.

    The customer's specs are:

    • Input voltage range: 9-16V
    • Output voltage: 5V
    • load current : 0-3.6A continous / peaks to be defined

    Could you share maybe some thoughts what we have to consider?

    Thanks and best regards
    Martin

  • 0 in reply to Martin Seeger
    TI__Expert 4100 points

    Hi Martin,

    Based on conditions you described this should be possible without any major limitations.

    As far as minimum SYNC frequency is concerned, guaranteed and tested value for this device is 250kHz, with wide range of duty cycles that can be accommodated (25 to 75%). There are really no other specific requirements (beyond datasheet specifications), as far as implementation is concerned.

    From application standpoint it should be noted that If device is operating in Auto Mode, then the device will not sync at no load or light loads. To prevent frequency foldback in low duty cycle conditions load of 200mA is needed.

    I hope this helps.

    Best regards

    Brani