LMX2820: LMX2820

Hi Vikas, 
If you're not finding any Vtune voltage I anticipate the LMX2820 device on your board is not locked... 
Can you probe LD to see if it's high? If LD is high, I anticipate Vtune to be around ~1.2V 

Using the LMX2820EVM can you load the default configuration and achieve lock using the directions outlined in the LMX2820EVM User's guide? 

Regards, 

Vicente 

Hi Prado

I did that in the morning , what you suggested . I loaded the default settings from , still no changes .

I have used 4th order filter as shown in SD .

Even though device is not locked , it should give some vtune right . Strange thing is , when I read the registers, it’s saying it’s matching, so I am not doubting the device also .

Regards

Vikas 

Hi Vikas, 

Vikas Kumar40 said:

when I read the registers, it’s saying it’s matching,

Are you saying you're able to program the device & reading back the registers results in the correct values being return? 

If the device is not locked, I anticipate the reference not being available. Is LD high? 
What is your refence clock at OSCIN? Is it available before programming LMX2820?

Regards, 

Vicente 

Hi

As on the TI eval board , which I am using to configure my custom board, after writing the registers , I tried to read few registers back . And it was reading the same data which was sent .

I am using 100 MHz CW signal . It’s available before programming . I checked at the pin as well , clk is reaching there.

LD is showing low only .

From the TI Eval board , I am taking CSB , SCK , SDI . CE I am connecting to 3.3 V on board only .

Regards 

Vikas 

Hi Vikas, 
Okay seems like you're configuring the device correctly. 

Does following the EVM Quick start guide lock the device? 

If the device locks, the LED will be lit. 

Regards, 

Vicente 

Hi Prado

On my custom board, I dont see any lock update.
What else can be checked.

Regards

Vikas 

Seems half problem is resolved . In the SPI interface , I hsvd replaced 0E with 12K , now I am able to get output frequency, though not locked . 

Now I should focus on loop filter .

Regards

Vikas 

Hi Vikas, 
Please Use PLLatinumSim to design loop filter. 

I take it you managed to create your configuration file on the EVM successfully then? Did you manage to get EVM to lock? 

Regards, 

Vicente 

I did not use the EVM for LMX2820, as I don’t have . I was using TI EVM for writing the configuration file to my designed board .

I simulated the values in Platinum only , seems some component mismatch is there in assembly.

Regards 

Vikas 

Now I am able to lock the PLL . Thanks a lot for the support .