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LMX2572: ..

Part Number: LMX2572

Hi,

1) maximum spi clk frequency mentioned in LMX2572 datasheet is 75Mhz. My code is working fine till 3Mhz, but after that I am not able to get output .

2)Also I want to generate ramp from 2400Mhz to 2500Mhz within 400 microseconds,

Below I have mentioned the TICS PRO format file for your reference . also i have attached the STM_32 feeded Registers value.what should be the sequence for writing the registers.

2.4ghz_ramp.tcs

2.4ghz_ramp.txt
R125	0x7D2288
R124	0x7C0000
R123	0x7B0000
R122	0x7A0000
R121	0x790000
R120	0x780000
R119	0x770000
R118	0x760000
R117	0x750000
R116	0x740000
R115	0x730000
R114	0x727802
R113	0x710000
R112	0x700000
R111	0x6F0000
R110	0x6E0000
R109	0x6D0000
R108	0x6C0000
R107	0x6B0000
R106	0x6A0007
R105	0x693EA3
R104	0x682710
R103	0x671EB8
R102	0x660005
R101	0x650001
R100	0x642710
R99	0x631EB8
R98	0x620014
R97	0x610008
R96	0x600000
R95	0x5F0000
R94	0x5E0000
R93	0x5D0000
R92	0x5C0000
R91	0x5B0000
R90	0x5A0000
R89	0x590000
R88	0x580000
R87	0x570000
R86	0x560000
R85	0x550000
R84	0x540001
R83	0x530000
R82	0x520200
R81	0x510000
R80	0x50CCCC
R79	0x4F004C
R78	0x4E0001
R77	0x4D0000
R76	0x4C000C
R75	0x4B0800
R74	0x4A0000
R73	0x49003F
R72	0x480001
R71	0x470081
R70	0x46C350
R69	0x450000
R68	0x4403E8
R67	0x430000
R66	0x4201F4
R65	0x410000
R64	0x401388
R63	0x3F0000
R62	0x3E00AF
R61	0x3D00A8
R60	0x3C03E8
R59	0x3B0001
R58	0x3A9001
R57	0x390020
R56	0x380000
R55	0x370000
R54	0x360000
R53	0x350000
R52	0x340421
R51	0x330080
R50	0x320080
R49	0x314180
R48	0x3003E0
R47	0x2F0300
R46	0x2E07F0
R45	0x2DC61F
R44	0x2C1FA3
R43	0x2B0000
R42	0x2A0000
R41	0x290000
R40	0x280000
R39	0x27FFFF
R38	0x26FFFF
R37	0x250205
R36	0x240030
R35	0x230004
R34	0x220010
R33	0x211E01
R32	0x2005BF
R31	0x1FC3E6
R30	0x1E18A6
R29	0x1D0000
R28	0x1C0488
R27	0x1B0002
R26	0x1A0808
R25	0x190624
R24	0x18071A
R23	0x17007C
R22	0x160001
R21	0x150409
R20	0x144848
R19	0x1327B7
R18	0x120064
R17	0x110096
R16	0x100080
R15	0x0F060E
R14	0x0E1820
R13	0x0D4000
R12	0x0C5001
R11	0x0BB018
R10	0x0A10F8
R9	0x090004
R8	0x082000
R7	0x0740B2
R6	0x06C802
R5	0x0530C8
R4	0x040A43
R3	0x030782
R2	0x020500
R1	0x010808
R0	0x00A11C

3)Also , I have written code on STM32 to generate ramp from 2400Mhz to 2500Mhz , But when I increase my ramp clock of LMX2572 from 30khz to 240khz, ramp is not generated properly, we are using EVAL board For Generation and the LOOP filter values are standard . do we need to Change it for better locking as we are getting spurious at fixed freq.

  • Hi There,

    In order to be able to run SPI at 75MHz, the interface between the logic device and the synthesizer should not contain any RC filter. 

    I will check the ramp issue tomorrow.

  • Hi There,

    I think the problem is due to VCO calibration.

    when we keep increasing or decreasing the VCO frequency, at some point, the device will need to perform a VCO calibration so as to pick the right VCO configuration to support the desired frequency. The calibration takes approx. 100µs to complete. 

    If your RampClk frequency is over 10kHz, the device may not have sufficient time to complete the VCO calibration. As a result, you will not get the correct output frequency.