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LMK04828: Shifting in the output frequency of PLL

Part Number: LMK04828

Hello Everyone,

I have an issue in the mentioned PLL and it goes line this, Simulation has been done for the conversion of 120MHz to 150MHz in TICS Pro simulator and export all the register values from the simulator. After that I load the file in my module which is having the LMK04828B PLL and I got the output of 150MHz with the shift of 1.2MHz. Refer the attached image of clkin and PLL selection, Clock outputs, and output frequency of 151.2MHz. Refer the register file also.

What might be the reason for that delay/shifting in the output frequency or shall I do any change in the simulator file?

Please check and provide me the best solution.

R0 (INIT)	0x000090
R0	0x000000
R2	0x000200
R3	0x000306
R4	0x0004D0
R5	0x00055B
R6	0x000600
R12	0x000C51
R13	0x000D04
R256	0x010070
R257	0x010155
R258	0x010255
R259	0x010300
R260	0x010420
R261	0x010500
R262	0x010690
R263	0x010716
R264	0x01086A
R265	0x010955
R266	0x010A55
R267	0x010B01
R268	0x010C22
R269	0x010D10
R270	0x010E99
R271	0x010F00
R272	0x011063
R273	0x011155
R274	0x011255
R275	0x011301
R276	0x011422
R277	0x011510
R278	0x011699
R279	0x011755
R280	0x011873
R281	0x011955
R282	0x011A55
R283	0x011B01
R284	0x011C22
R285	0x011D00
R286	0x011E99
R287	0x011F11
R288	0x012078
R289	0x012155
R290	0x012255
R291	0x012301
R292	0x012402
R293	0x012510
R294	0x012698
R295	0x012700
R296	0x012878
R297	0x012955
R298	0x012A55
R299	0x012B01
R300	0x012C02
R301	0x012D00
R302	0x012E89
R303	0x012F01
R304	0x01306F
R305	0x013155
R306	0x013255
R307	0x013301
R308	0x013422
R309	0x013510
R310	0x013689
R311	0x013711
R312	0x013801
R313	0x013902
R314	0x013A02
R315	0x013B00
R316	0x013C00
R317	0x013D08
R318	0x013E03
R319	0x013F08
R320	0x014081
R321	0x01410D
R322	0x014200
R323	0x014311
R324	0x01440F
R325	0x01457F
R326	0x014603
R327	0x01471A
R328	0x014802
R329	0x014942
R330	0x014A02
R331	0x014B16
R332	0x014C00
R333	0x014D00
R334	0x014EC0
R335	0x014F7F
R336	0x015003
R337	0x015102
R338	0x015200
R339	0x015300
R340	0x015419
R341	0x01551A
R342	0x015640
R343	0x015700
R344	0x015896
R345	0x015903
R346	0x015AC0
R347	0x015BD4
R348	0x015C20
R349	0x015D00
R350	0x015E00
R351	0x015F0B
R352	0x016000
R353	0x016101
R354	0x016225
R355	0x016300
R356	0x016400
R357	0x01650A
R369	0x0171AA
R370	0x017202
R380	0x017C15
R381	0x017D33
R358	0x016600
R359	0x016700
R360	0x016805
R361	0x016959
R362	0x016A20
R363	0x016B00
R364	0x016C00
R365	0x016D00
R366	0x016E13
R371	0x017300
R386	0x018200
R387	0x018300
R388	0x018400
R389	0x018500
R392	0x018800
R393	0x018900
R394	0x018A00
R395	0x018B00
R8189	0x1FFD00
R8190	0x1FFE00
R8191	0x1FFF53

  • Hello Kingslin,

    I see two immediate issues:

    1. Maximum Fpd of PLL2 for LMK04828 is 155MHz. You should disengage the doubler. (There is no warning from TICS Pro about this misconfiguration, so I apologize for this error - I've fixed it and it will be clearer in subsequent TICS Pro releases)
    2. 2400MHz is not a supported VCO frequency on LMK04828. 3000MHz is, with VCO1; you could set the N Prescaler to 5, the N divider to 5, and the N Cal Divider to 5. The channel divider would be set to 20 to produce 150MHz.

    On the current version of TICS Pro, 2400MHz VCO should have colored the VCO box red and indicated this is an impossible frequency target. I'm not sure which version of TICS Pro you're using, but I suggest downloading the latest version from TI.com.

    Regards,

    Derek Payne

  • Hi Derek Payne,

    Thanks for the information. As stated above, the mentioned frequency and divider settings has been kept. PLL is generating the power level of 150MHz but the spurious level is near to the fundamental frequency(150MHz).

    Refer the attached image of settings and the output of the PLL. What might be the issue for that spurious level?

    Please provide the best solution to avoid the spurious level.

    Note : The reference frequency is 120Mhz which is generated from OCXO Module and also from signal generator. In both cases the spurious level is not suppressed.

    R0 (INIT)	0x000090
    R0	0x000000
    R2	0x000200
    R3	0x000306
    R4	0x0004D0
    R5	0x00055B
    R6	0x000600
    R12	0x000C51
    R13	0x000D04
    R256	0x010074
    R257	0x010155
    R258	0x010255
    R259	0x010300
    R260	0x010420
    R261	0x010500
    R262	0x010690
    R263	0x010716
    R264	0x01086A
    R265	0x010955
    R266	0x010A55
    R267	0x010B01
    R268	0x010C22
    R269	0x010D10
    R270	0x010E99
    R271	0x010F00
    R272	0x011063
    R273	0x011155
    R274	0x011255
    R275	0x011301
    R276	0x011422
    R277	0x011510
    R278	0x011699
    R279	0x011755
    R280	0x011873
    R281	0x011955
    R282	0x011A55
    R283	0x011B01
    R284	0x011C22
    R285	0x011D00
    R286	0x011E99
    R287	0x011F11
    R288	0x012078
    R289	0x012155
    R290	0x012255
    R291	0x012301
    R292	0x012402
    R293	0x012510
    R294	0x012698
    R295	0x012700
    R296	0x012878
    R297	0x012955
    R298	0x012A55
    R299	0x012B01
    R300	0x012C02
    R301	0x012D00
    R302	0x012E89
    R303	0x012F01
    R304	0x01306F
    R305	0x013155
    R306	0x013255
    R307	0x013301
    R308	0x013422
    R309	0x013510
    R310	0x013689
    R311	0x013711
    R312	0x013821
    R313	0x013902
    R314	0x013A02
    R315	0x013B80
    R316	0x013C00
    R317	0x013D08
    R318	0x013E03
    R319	0x013F08
    R320	0x014081
    R321	0x01410D
    R322	0x014200
    R323	0x014311
    R324	0x01440F
    R325	0x01457F
    R326	0x014603
    R327	0x01471A
    R328	0x014802
    R329	0x014942
    R330	0x014A02
    R331	0x014B16
    R332	0x014C00
    R333	0x014D00
    R334	0x014EC0
    R335	0x014F7F
    R336	0x015003
    R337	0x015102
    R338	0x015200
    R339	0x015300
    R340	0x015419
    R341	0x01551A
    R342	0x015640
    R343	0x015700
    R344	0x015896
    R345	0x015903
    R346	0x015AC0
    R347	0x015BD4
    R348	0x015C20
    R349	0x015D00
    R350	0x015E00
    R351	0x015F0B
    R352	0x016000
    R353	0x016101
    R354	0x0162A4
    R355	0x016300
    R356	0x016400
    R357	0x016505
    R369	0x0171AA
    R370	0x017202
    R380	0x017C15
    R381	0x017D33
    R358	0x016600
    R359	0x016700
    R360	0x016805
    R361	0x016959
    R362	0x016A20
    R363	0x016B00
    R364	0x016C00
    R365	0x016D00
    R366	0x016E13
    R371	0x017300
    R386	0x018200
    R387	0x018300
    R388	0x018400
    R389	0x018500
    R392	0x018800
    R393	0x018900
    R394	0x018A00
    R395	0x018B00
    R8189	0x1FFD00
    R8190	0x1FFE00
    R8191	0x1FFF53
    

    Thanks in Advance,

    Kingslin J,

    RF Design Engineer,

    Data Patterns(India) Ltd.

  • Kingslin,

    Your spur levels are very high, and this is unusual. This is an integer PLL, there shouldn't really be any spurs at that magnitude or offset. This shouldn't be coming from either the PLL or the VCO. I would expect this to be part of the reference, or part of the power supply.

    • Have you checked the spectrum on your reference? Are you certain there is no spur at the observed offset? 
    • Is the on-board 122.88MHz VCXO for the EVM disabled (supply ferrite removed to prevent any spurious coupling between VCXO and OSCin signal)?
    • What power supply are you using? Is it a switching supply, potentially at around 1.3 MHz?

    Regards,

    Derek Payne