LTC3633A output coupling switching noise

Hi all,

Our customer will be going to select power IC, mult ch output.
They will be concerned the output coupling, and switching noise.

In the datasheet LTC3633A, page 12 "OPERATION" say following.
"One potential disadvantage to this configuration occurs when one channel is operating at 50% duty cycle.
In this situation, switching noise can potentially couple from one channel to the other, resulting in frequency jitter on one or both channels.
This effect can be mitigated with a well designed board layout."

Why occur to couple at 50% duty cycle ?
, and the condition is 50% duty cycle only ?

Best regards,
sss

  • 0
    •  Analog Employees 
    on Feb 26, 2018 9:23 PM

    In this case (180 out of phase), one channel turn-on edge aligns with the turn-off edge of the other channel. Cross-talk happens, but better layout helps. LTC3636 has the same spec, but with improved jitter performance.  One other choice is LTC7124. 

  • JoshYe - san,

    Thank you for reply.

    Would you mind to provid the typical performance data to consider the Cross-talk performance, if possible ?
    for example, output vs SW frequency etc.

    The customer is now considering LTC3633A and LTM4644, and are requesting the there reference data, for the designning device setting and PCB design.

    Best regards,

    sss

  • 0
    •  Analog Employees 
    on Mar 1, 2018 11:34 PM

    Cross-talk can be mitigated by placing the input cap close to the LTC3633A, and the output cap close to the inductor.  You can find layout recommendations on pg 21 and pg 23 of the datasheet.

    Typical performance data is not very useful in this scenario as it depends heavily on layout and configuration.  With separate outputs, the risk of output coupling is low, especially since the different SW pins are on opposite sides of the package.