LMX2571: LMX2571 - restrictions for N-divider

Alexander,

PLLatinum Sim says minimum Divide is 24, but I don't think this is very updated.  Recall that there is a pre-n divider of 2, so that's really PLL_N = 12.

But TICSPro is more believable and it shows the following.

Regards,
Dean

# Validate PLL N divider
MinN = -1
if (flexFRAC_ORDER.iValue==0):
MinN=6
elif (flexFRAC_ORDER.iValue==1):
MinN=6
elif (flexFRAC_ORDER.iValue==2):
MinN=11
elif (flexFRAC_ORDER.iValue==3):
MinN=22
else:
MinN=22

Alexander,

For the LMX2571, which was your first email, PLLatinum Sim would not mention PFD_DELAY, but for TICSPro, it should say in accordance to page 28

Used to optimize spurs and phase noise. Suggested values are:
Integer mode (NUM = 0): use PFD_DELAY ≤ 5
Fractional mode with N-divider < 22: use PFD_DELAY ≤ 4
Fractional mode with N-divider ≥ 22: use PFD_DELAY ≥ 3

Regards,
Dean

Hi Alex,

The VCO tuning range is very narrow in LMX2571, there is no VCO frequency dependence of PFD_DELAY.