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LMX2571: LMX2571 register configuration

Harry Ma
Intellectual 2670 points
Part Number: LMX2571

Hi Team

Customer wanna using an external VCO to output 455.66MHz. and configure SPI port with 4 wires. The reference frequency is 122.88MHz  and the reference frequency is single-ended input, the phase detection frequency is 61.44MHz.

The configuration and register and schematic show as below, but it works abnormal and can't lock.  Can you help review if there is any fault?

Fullscreen LMX2571 HexRegisterValues 2.txt Download 
R60	0x3CA000
R58	0x3A8C00
R53	0x357806
R47	0x2F6000
R46	0x2E001A
R42	0x2A021E
R41	0x290870
R40	0x28101C
R39	0x2711FB
R35	0x230C83
R34	0x221000
R33	0x210000
R32	0x200000
R31	0x1F0000
R30	0x1E0000
R29	0x1D0000
R28	0x1C0000
R27	0x1B0000
R26	0x1A0000
R25	0x190000
R24	0x18000E
R23	0x170E84
R22	0x168584
R21	0x150101
R20	0x14301B
R19	0x1303E8
R18	0x120000
R17	0x110000
R16	0x100000
R15	0x0F0000
R14	0x0E0000
R13	0x0D0000
R12	0x0C0000
R11	0x0B0000
R10	0x0A0000
R9	0x090000
R8	0x0800EE
R7	0x070EC4
R6	0x068441
R5	0x050101
R4	0x04000B
R3	0x031200
R2	0x0232FE
R1	0x017A0F
R0	0x000082

  • +1
    TI__Genius 12560 points

    Hi,

    For 455.66MHz external VCO with 61.44MHz PFD frequency, PLL_NUM_F1 value is not correct in your config. It needs to be "3330729". Also R-divider should be 2 for divided PFD frequency. You can try with below changes and see the performance.

    Schematic doesn't show the CPoutExt (pin 30) connection to external VCO with loop filter components. I assumed, it should be there. If not, provide the connection.

    Thanks!

    Regards,

    Ajeet Pal