CDCE62002: CDCE62002 - Wrong output frequency

Hello,

So to clarify. You have two configurations: 74.25 MHz to 74.25MHz and 148.5 MHz to 148.5 MHz. And the problem arises when you are switching from the 74.25 MHz config to the 148.5 MHz config and vice versa, correct? Can you provide your 74.25 MHz config as well? And does this config have the same external filter values? We can try to reproduce this issue on the bench.

Best,

Cris

Hi Cris,

Below is my 74.25 MHz configuration:

Reg0: 0x10660050
Reg1: 0x9782E021

The external filter always has the same values whatever the frequency is.

Hello,

We will try to replicate this issue on the bench. Expect an update later this week.

Best,

Cris

Hello,

So far, I have not been able to replicate the issue. I have some additional questions.

Pierre161803 said:

Most of the time, the output frequency is correct; however, sometimes it's not.

- How often does the issue occur? One out of 10? One out of 50? 

- Is this only occurring on one device? 

Pierre161803 said:

The problem arises exclusively when transitioning the input signal from one frequency to another

- What is the order of the input frequency change, rewrite the device, toggle PD for recalibration sequence? What is the timing between each step?

Best,

Cris

Hi Cris,

Turns out I had it wrong about the problem just popping up with frequency changes.
After some digging, I realized it's actually triggered by high ambient temperatures (above +65 °C).
You can replicate it by simply reconfiguring the PLL multiple times; no need to tweak the frequency.
The issue occurs on every device.

I managed to nail down the correct register configuration using the internal filter (I was using the external one before):
R0: 0x10360050
R1: 0x8382E061
Now it works pretty well.

Got any idea why the external filter doesn't work well with high temperatures?

Here's how I'm setting things up:
1) Write R0 register
2) Write R1 register
3) Set PD = 0 (R2 = 0x01001802)
4) Wait 50 ms
5) Set PD = 1 (R2 = 0x01001002)
6) Wait 50 ms
7) Set PD = 0 (R2 = 0x01001802)
8) Wait 50 ms
9) Wait until the PLL is locked (bit 6 of register 2)

Hello,

Are you using one of our EVMs or your own PCB? If you are using your own PCB, can you share your schematic and layout?

Best,

Cris

Hi,

I use my own board.

Here's the schematic:

Hello,

Thank you. We will look into this and get back to you tomorrow.

Best,

Cris