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LMK04832: LDOs for LMK04832

Part Number: LMK04832
Other Parts Discussed in Thread: LMK04828, LMX2820

Hi Team,

We are using five LMK04828 in our design. For power supply, we are planning to use separate LDOs as per the Xilinx Clock 104 board (in clk104, 8 LDOs are used for individual power rails of  LMK0428 for better noise rejection). But LMK04828 reference design from TI (ADC12DJ3200EVM) uses single LDO for all power supply of LMK04828. Is it possible to use single LDO and use ferrite beads for powering LMK04828 since we have board area constraints and want to reduce number of LDOs. What is the most critical power rails of LMK04828 is recommended to use external LDOs. Our requirement is to have very low noise supply for LMK04828.

Also we know that LMK04828 and LMX2820 has internal LDOs and we want to know the value of internal LDOs PSRR and output noise ripple.

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Thanks and Regards,

Kiran Kumar

DTB-05007-01_A02_HW-CLK-104_121.pdf

  • Hello Kiran,

    It is possible to use a single LDO and ferrite beads for better noise isolation. Please see section 11 as well as figure 41 in the LMK04828 datasheet for a comprehensive explanation of power supply recommendations, including when bypassing is necessary, when ferrite beads are necessary, what power supply rails can be combined, etc.

    We do not characterize the internal LDO PSRR or output noise ripple. Our design simulations typically show >60dB PSRR below 1MHz on the LDOs for the VCOs, with effectiveness falling off at higher frequencies (hence the ferrite beads). Output LDOs are typically >40dB PSRR below 1MHz; PSRR is slightly more relaxed performance due to the inherent differential rejection for the outputs.

    Regards,