LMX2824EPEVM: Full assist mode of tuning, send R0?

Hi John,

did you check the example in the EVM user's guide?

https://www.ti.com/lit/pdf/snau308

Hi Noel,
Yes, I did check that but didn't see enough details.

If I enable double-buffering, then I need to send R0 to load the registers.

When I program R0 though things don't tune correctly.  I'm guessing I don't have the bits set correctly in R0 for full assist.

With the LMX2595, I didn't program R0 when tuning in full assist mode.

In my setup, I'm using a 10 MHz data rate so just looking to cut 15 us (6 registers, 2.5 us each) from the tune time.

Thanks,
John

Hi John,

With double buffering enabled, we need to program R0 to make all the change effective. FCAL_EN should therefore be =0 otherwise there will be a VCO calibration although the calibrated data is ignored in full assist mode.

Maybe your problem is on the VCO_FASTCHG_CNT, since your input is 10MHz, you can program this field to 50'd, CAL_CLK_DIV should be =0 to match the input frequency. 

Hi Noel,

Is VCO_FASTCHG_CNT the same thing as FASTCHG_CYCLES?

If SM cycles means State Machine cycles and these are based on OSCIN, my oscillator input is 100 MHz (my SPI is 10 MHz).

With the default settings of FASTCHG_CYCLES=250 and SMCLK_DIV=3, I come up with 20 us [1/(100MHz/8)*250] for the fast charge ON time.

I will experiment with these values and see if I can get double-buffering to work in full-assist.

I did try setting all the calibration bits in R0[2,3,12,13] to 0 to disable, but was never get double-buffering to work in full-assist.

Thanks,
John

I tried messing around with those register values but could never get the combination of double-buffering and full-assist to work.

I can make full-assist tuning work without double-buffering (R0 not sent).

I can make no-assist tuning work with double-buffering (R0 sent).

If you have any other thoughts on what else to try, please let me know.

Thanks,
John

Hi John,

I assume you were using your code to program the device.

Do you have a configuration I can use to setup TICS Pro and verify?

Hi Noel,

I'm using a 100 MHz reference frequency with the reference doubler enabled to produce a 200 MHz phase detector frequency.

I'm operating the device in fractional-n mode to produce a 25 MHz step size (denom=8).

Below are the register values I used to initialize (after resetting the PLL).  After initialization, I send R3, R5, R6, R14, R8 and R0 to try to tune in full assist mode.

Thanks,
John

Hi John,

I used TICS Pro default configuration and then plugged in your initialization setting, I got this.

1. OUTMUX=0, so Output MUX is pin control. That is, whether the output is direct VCO, divide down or VCO doubler output is controlled thru pin strapping. If this is not your intention, set OUTMUX = 1. 

2. Are you going to mute output B?

3. If you do not need VCO doubler, FCAL_DBLR_LE should be =0. 

4. CAL_CLK_DIV setting does not match with the reference clock frequency. This is not a big deal since you will use full assist. 

5. Only these 3 registers will be double buffered. Other related registers such as PLL_NUM and VCO doubler parameters will not be double buffered. 

Your initialization programs only a few registers, please program all the registers, from R79 to R0 because the application settings may not be identical to the silicon reset setting.

I suggest use the follow configuration for LUT creation.

1, READBACK should be =1 to read back the calibrated data.

2. if VCO doubler is needed, set FCAL_DBLR_EN = 1

3. read back these data

R79	0x4F0003
R78	0x4E0005
R77	0x4D0005
R76	0x4C000A
R75	0x4B0041
R74	0x4A0005
R73	0x4919B9
R72	0x481C80
R71	0x470002
R70	0x46FF00
R69	0x450020
R68	0x440004
R67	0x430000
R66	0x420000
R65	0x410000
R64	0x400022
R63	0x3F8000
R62	0x3E0008
R61	0x3D0080
R60	0x3C0000
R59	0x3B4180
R58	0x3A0300
R57	0x390300
R56	0x381FA4
R55	0x374400
R54	0x361E55
R53	0x350F83
R52	0x34C3E0
R51	0x33318C
R50	0x32318C
R49	0x310C16
R48	0x304419
R47	0x2F0030
R46	0x2E071A
R45	0x2D0881
R44	0x2C80C9
R43	0x2BB8FC
R42	0x2A1000
R41	0x290EB0
R40	0x282815
R39	0x277802
R38	0x260D38
R37	0x2503E8
R36	0x240021
R35	0x230000
R34	0x220000
R33	0x210000
R32	0x200327
R31	0x1F0000
R30	0x1ED6D8
R29	0x1D0000
R28	0x1C03E8
R27	0x1B0000
R26	0x1A01F4
R25	0x190000
R24	0x181388
R23	0x170000
R22	0x160001
R21	0x150210
R20	0x140000
R19	0x1301F8
R18	0x120008
R17	0x111001
R16	0x100001
R15	0x0F0000
R14	0x0E0000
R13	0x0D0000
R12	0x0C0000
R11	0x0B0000
R10	0x0A0008
R9	0x090000
R8	0x080046
R7	0x077D00
R6	0x0600BF
R5	0x054B2C
R4	0x040644
R3	0x035861
R2	0x020F2D
R1	0x013001
R0	0x00238C

To use the LUT, first of all, initialize the device with the following configuration.

This is again a no-assist calibration with MUXOUT set as lock detect output. The reason using no-assist calibration for initialization is to ensure the lock detector will response in full assist mode. 

After initialization, now enable full assist mode.

1. make change to these bits. Set FCAL_EN and FCAL_DBLR_EN = 0 first.

2. use the data from LUT to program these registers

3. Program R0 to make the change effective.