LMX2572EVM: LMX2572 Full Assisted Calibration lock time is much longer than the datasheet claims - sometimes >1ms

Hi Jason,

If you do full assist, you do not need to program R0 (to initiate calibration) unless you have some other bits in R0 needed to be change. 

Since you just want to change frequency, you don't need to write all registers. In your example, you only need to update N divider and the three VCO parameters.

Use the LD pin to measure lock time is not accurate enough. We used to use a test equipment capable of measuring freq vs time to measure the lock time. 

In your example, there are two more things that are misleading your measured lock time.

TICS Pro has default the LD_TYPE to "Vtune and VCOCal". That is, the lock detect will turn HIGH only when VCO calibration is finished and the Vtune voltage is within a certain range. With full assist, you don't need calibration (but you did program R0 to trigger calibration), so this lock time measurement is invalid. 

Furthermore, LD_DLY is default to 1000. This is a delay added after VCO calibration is finished. Lock detect cannot change it status before the delay is over. 

In short, you have got similar "lock time" because it was the time taken for VCO calibration + a pre-defined delay time.

in this example, the suggested programming sequence is:

1. Program R16: VCO_DACISET
2. Program R19: VCO_CAPCTRL
3. Program PLL_N
4. Program R8: VCO_DACISET_FORCE=1; VCO_CAPCTRL_FORCE=1
5. Program R20: VCO_SEL; VCO_SEL_FORCE=1 (you can skip this step as the VCO core did not change at all)

Hi Noel,

This is great thanks.

I don't have any test equipment that can output freq vs time - will the rb_LD_VTUNE field in register 110 give a good indication of lock or is this invalid in full assist?

Is there a later version of the datasheet than RevB ? None of this is clear from the current datasheet

Also: in your programming sequence

1. Program R16: VCO_DACISET
2. Program R19: VCO_CAPCTRL
3. Program PLL_N

does the PLL_N wite have to come after the VCO DAC and CAP writes?

If the VCO core is changing does that have to happen last? 

for frequency switches across a wider range I need to write to many more registers - chdiv, PLL_NUM, PFD_DLY_SEL etc

do you have a more complete description of the programming sequence for full assist across the whole range of the device?