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LMK04610EVM: power supply decoupling

vic zap
Intellectual 740 points

Part Number: LMK04610EVM
Other Parts Discussed in Thread: LMK04610

Hi!

In the LMK04610 EVM you decouple the supply pins of the LMK04610 with ferrite beads and 10 uF and 0.1 uF ceramic capacitors - L5, C113, C115 for VDD_CORE; L7, C121, C123 for VDD_PLL1 and so on for every supply pin (see SNAU201A – January 2017 – Revised February 2017, page 25).

Such a configuration forms a hi Q LC-circuit, i.e. the voltage on the corresponding supply pin will oscillate in response to rapid changes of the current flowing through the pin.

Are the currents through the supply pins of the LMK smooth enough not to cause the decoupling circuit to oscillate or perhaps this effect is not important enough to be considered? Would it be more robust to replace 10 uF ceramic capacitors in the current configuration with 10uF tantalum with certain esr to lower the Q or to add bulk tantalum capacitors to the current configuration to damp out any resonance? Is it a good practice to use ferrite beads with low esr ceramic capacitors without any damping?

Thanks in advance!

Best regards, Vic.

  • 0
    TI__Mastermind 32575 points
    The supply current may change during device register initialization, but should be stable thereafter. In general, when using ferrite bead for supply filtering, it is not a bad idea to consider use of lossy ferrite bead (with small DCR) and/or decoupling cap with small ESR (e.g. tantalum, controlled-ESR ceramic, or discrete resistor in series with the dcoupling cap) to reduce any resonance of the LC circuit. This should be given consideration if a switching regulator is used to power the device, so it does not boost the switching noise/ripple.

    Alan
  • 0 in reply to Alan O
    Intellectual 740 points

    Thank you for the answer, Alan!

    Can you tell me please, what is the primary purpose of the filters used in the EVM (L5, C113, C115 for VDD_CORE; L7, C121, C123 for VDD_PLL1 and so on for every supply pin)? Is it intended to filter switching regulator noise or to prevent noise generated by the LMK itself from further propagating to the common supply rail?

    Best regards, Vic.

  • 0 in reply to vic zap
    TI__Mastermind 32575 points
    The filters serve both purposes you mentioned, but attenuating switcher noise to the device supply pins is the primary reason.

    Alan
  • 0 in reply to Alan O
    Intellectual 740 points

    Thanks a lot for the replies, Alan!

    Best regards, Vic.