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LMK03200 VCC Bypassing recommendations?

Dennis McCal
Prodigy 100 points
Other Parts Discussed in Thread: LMK03000, LMK03200

LMK03200 & LMK03000 series have no recommendations related to bypassing the 14 VCC pins on the chip in their data sheets. I noticed (from a note on the forum) that LMK04800 series has a nice note discussing which VCC pins are related to which output Clock and best practices for bypassing them. I also looked at the EVAL board schematic for the LMK03200 and it is not really clear which caps do what since there is no placement information. I couldn't find any EVAL PCB Gerbers or other useful placement tools to look for guidance.

Are the individual VCCx pins tied to specific outputs? I only need one of the 8 outputs in my application and would prefer to only bypass for that channel if possible to save lay out time and unnecessary components in production. 

Are there notes to help with this somewhere?

thanks

Dennis

  • 0
    TI__Mastermind 32575 points

    Hi Dennis,

    The output Vcc pins are adjacent to each output pair.  If an output pair is not used, its Vcc pin should still be powered but the driver can be disabled/powered-down via register to reduce current.  Each output Vcc should have 0.1 uF nearest the Vcc pin, but may be omitted for any output that is disabled.  A ferrite bead may be placed between the clean 3.3V power plane and 0.1uF bypass cap (nearest each Vcc pin) to isolate any Vcc switching noise from coupling to the power plane.  A ferrite bead may be shared between Vcc pins for outputs running at the same frequency. 

    • Vcc3: CLKout0
    • Vcc4: CLKout1
    • Vcc5: CLKout2
    • Vcc6: CLKout3
    • Vcc11: CLKout4
    • Vcc12: CLKout5
    • Vcc13: CLKout6
    • Vcc14: CLKout7

    All other Vcc pins (Vcc1-2, Vcc7-10) are used by the PLL/CP and VCO blocks.  These Vcc pins can be tied directly to the clean 3.3V power plane.  Each of these Vcc pins should have a 0.1 uF bypass cap (nearest each pin). 

    A few local decoupling caps (e.g. 4x 10-22 uF, 4x 1 uF) should also be used on the 3.3V power plane and placed nearby around the chip to act as local charge reservoirs for the smaller decoupling caps.

    Hope this helps. 

    Regards,
    Alan

    Please click Verify if I answered your question.

  • 0 in reply to Alan O
    Prodigy 100 points

    Alan,

    Thanks, that is exactly what I needed. Especially for the output pins that are not being used saves a lot of layout details that aren't needed. 

    Dennis