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LMX2572EVM: Removing unneeded parts

Part Number: LMX2572EVM
Other Parts Discussed in Thread: USB2ANY


I wanted to use the LMX2572EVM to produce a continuous wave signal (~4.5 GHz). My main requirement is phase noise and stability. I will be using an external oscillator. I wanted to use the evaluation board as a baseline for our design but remove parts that are not needed in order to miniaturize the footprint.

Can you please advise on what parts (caps/resistor/etc) can be removed without affecting performance? 

  • Hello Mohamed,

    Referring to the EVM schematic, the following components are provided only for evaluation purposes and can be omitted in a final design:

    • The resistors to VCC (R36, R41, R42, R43, R44, R45) can be shorted
    • The DNP termination components on the outputs (L1, L2, C6, C11, R37, R38, R39, R40) can be removed
    • Depending on the OSCin termination scheme, many of the input path components (R24, R25, R26, R29, R30, R31) could be removed or populated selectively. For example, if the input will be provided as 100MHz LVDS, R32 could be populated with 100Ω and all other termination components could be removed or shorted as needed.
    • Optionally, some of the loop filter components may be removed. If it is known that a 2nd order loop filter will satisfy phase noise and lock time requirements, C1_LF and C3_LF could be removed and R3_LF/R4_LF could be shorted.
    • If the RAMPCLK, RAMPDIR, SYNC, or SYSREFREQ pins are needed, the connections could be simplified. If they are not needed, they could be shorted to GND.
    • Essentially all components on page 2 of the schematic are superfluous for application use, and are only provided for evaluation with USB2ANY, or to evaluate performance with a switching power supply.

    Components which are critical:

    • The bypass capacitors on the supply (C18, C23, C26, C27, C29, C30)
    • The bypass capacitors on the internal LDOs and bias points (C19, C20, C21, C22, C24, C25, C28)
    • The input coupling capacitors (C14, C15) and output coupling capacitors (C5, C7, C10, C12)

    Note that all critical capacitors and their values are described in the pin descriptions of the datasheet.