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LMX2592: More on Frequency Drift

Part Number: LMX2592

Case 1: LMX2592RHAT set to 9750MHz: frequency drifts to 9750MHz + 15MHz after1 second when programmed using the MSP430FR5969IRGZR microcontroller; when using the USBANY programmer (MSP430FR5969IRGZR in reset mode (tristated) everything works fine.

Case 2: LMX2592RHAT set to 8490MHz: frequency drifts to 8490MHz + 11MHz after1 second when programmed using the MSP430FR5969IRGZR microcontroller; when using the USBANY programmer (MSP430FR5969IRGZR in reset mode (tristated) everything works fine.

Note: circuit topology exactly the eval board except the loop filters.

Thanks for your support,

Randy

  • Hi Randy,

    make sure your programming sequence is correct.

    1. Apply Vcc power supply to the device.

    2. Provide a valid reference clock to the device

    3. (optional) program RESET = 1

    3. Program all registers in descending order. That is, R70 -> R69 -> R68 -> ..... -> R2 -> R1 -> R0 (FCAL_EN must be equal to 1)

  • Hi Noel,

    Thanks for your reply.

    I will implement the programming sequence you outlined here. I will be bypassing the MSP430 to isolate the problem.

    Regards,

    Randy

  • Hi Noel,

    We implemented the above sequence and the 8490MHz output doesn't drift by ~15MHz anymore as seen from the N9041B signal analyzer using a narrow span. However, the phase noise has deteriorated to ~ -60dBc/Hz. Also, the lock detect pin sporadically toggles between high and low.  Attached is a video footage showing the tone slowly going to the center frequency after programming. On the other hand, using the USBANY programmer with the MSP430 tri-stated, the tone snaps to center frequency instantaneously and the phase noise is -98dBc/Hz with the lock detect showing a stable high.

    Any feedback on these findings? Today, we are going to capture the whole programming sequence of MSP430 vs. USBANY and compare bit by bit.

  • Hi Randy,

    How fast is your MSP430 programming speed? Could you do one more R0 programming 10ms after all the registers are programmed?

    that is, from the previous suggested programming sequence:

    3. Program all registers in descending order. That is, R70 -> R69 -> R68 -> ..... -> R2 -> R1 -> R0 (FCAL_EN must be equal to 1)

    4. wait 10ms

    5. Program R0