LMX2820: PLL Not Locking - Low temperature, no output doubler

Hi,

Our LMX2820 board is giving issues at low temperatures (below 10C), and we are seeing the same behaviour on the EVM.

Here are the frequencies giving problems and their corresponding settings:

I've done several tests using instant calibration and fully-assisted calibration, with mixed results.

The calibration and setup works perfectly up to +80C, we are only seeing locking issues below 10C.

Here are the descriptions and results from two tests performed with the EVM, one using instant cal, the other one not using instant cal. I'm cycling the only three frequencies in our spectrum that does not use the VCO doubler. All other frequency points work exactly as expected at any temperature.

Test 1:

• Power cycle and initialize
• Instant calibration
• Cycle frequency points in the table from min->max
• Monitor lock detect and capture spectrum

First frequency, no lock:

Second frequency, locked:

Third frequency, no lock:

Test 2:

• Power cycle and initialize
• Fully assisted calibration
• Cycle frequency points in the table from min->max
• Monitor lock detect and capture spectrum

Results from Test 2:

The instant calibration setup procedure used is described here LMX2820: Instant Cal - Clock & timing forum - Clock & timing - TI E2E support forums.

Thanks in advance.