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LMX2594EVM: Lock time vs SPI Frequency

Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594

Hi,

I've done some tests with the LMX2594 using several frequencies for the SPI write speed. My results are given below

Time Last Data / CSB Rising Edge [µs] Time CSB Rising Edge / LD Rising Edge [µs] Time Last Data / LD Rising Edge SPI writing speed [kHz]
19 2,5 21,5 100
22 3,6 25,6 500
1 26 27 1000
1,4 25 26,4 5000
1,5 26 27,5 10000
1,8 26 27,8 50000

Red trace is Data

Yellow trace is CSB

Green trace is Clk

Blue trace is Lock Detect

I have used a Raspberry Pi 3 B+ to control the LMX2594 (instead of the Reference Pro), and the Full Assist mode. As you can see, the time between the last bit of one word and the lock detect rising edge is relatively stable. However that's not the case between the CSB rising edge and the Lock Detect rising edge.

I would like to know what signal triggers the whole processus which allows the PLL to be locked ? Is that the last data bite or the CSB ?

Thanks for the answer

Stéphane

  • Hi Stéphane,

    You can measure the distance between the rising edge of CSB and the rising edge of MUXout pin (configured as lock detect) to estimate lock time.

    Keep in mind that this result is only VCO calibration time. The true lock time is VCO calibration time + Analog setting time. To accurately measure lock time, we use phase noise analyzer in transient mode, as shown in Figure 12 of datasheet.

    Regards,

    Hao