LMX2594: Output of MUXout pin

user5959213

Part Number: LMX2594

Hi all，

The MUXout pin of lmx2594 on my board is used for Lock Detect,LD_TYPE is set to 1 and LD_DLY is set to 1000.

When the pll is unlocked on my board,i measured the output of MUXout pin without anything writing,the waveform is as follows，

From which we can see a low level sometimes, but there is a period of high level about 260us,Why?Is this normal?I always thought that if the PLL is out of lock, then the muxout should always be low level.

I can see the pll is indeed unlocked from spectrum in the meanwhile.

over 4 years ago

0 Noel Fung over 4 years ago

TI__Guru** 109470 points

Hi There,

Could you also measure the waveform of Vtune pin for us to brainstorm? Thank you.

0 user5959213 over 4 years ago in reply to Noel Fung

Intellectual 865 points

Hi Noel,

The waveform of Vtune pin is as follows,

The green line is the waveform of MUXout pin ,the yellow line is the waveform is Vtune pin,and the one segment of enlarged picture is like this,

0 Vibhu Vanjari over 4 years ago in reply to user5959213

TI__Genius 11900 points

Hello,

This is very interesting, it looks like the tuning voltage drops and self recovers. You are not writing any other register correct?

Do you see any different behavior when using LD_DLY = 0 or LD_TYPE = 0?

Thanks,

Vibhu

0 user5959213 over 4 years ago in reply to Vibhu Vanjari

Intellectual 865 points

Hi Vibhu,

Yes,i didn't writing any reg about lmx2594,i just made the clock which offered reference for 2594 unlocked.I also checked the clock's LD which is always low level.

I have tried LD_DLY=0 and LD_TYPE=0,the waveform of LD pin is always high,and the waveform of the Vtune isn't changed.

0 Noel Fung over 4 years ago in reply to user5959213

TI__Guru** 109470 points

Hi There,

What is the frequency of the pulse? it is equal to the fpd?

The reference is "unlock", I assume that means there is reference clock signal but the frequency is not correct, true?

0 user5959213 over 4 years ago in reply to Noel Fung

Intellectual 865 points

Hi Noel,

1.The pulse cycle of time domain is about 35ms.No,it is not equal to Fpd(Fpd is 184.32M in my case).

2.Yes.

0 Noel Fung over 4 years ago in reply to user5959213

TI__Guru** 109470 points

Hi There,

What is the reference clock frequency when it is locked and unlocked?

What is the target LMX output frequency?

0 user5959213 over 4 years ago in reply to Noel Fung

Intellectual 865 points

Hi Noel,

The ref clk is 368.64M when it is locked and it is 361.526M but it is wandered when unlocked.

The output frequency is about 12300M.

0 Noel Fung over 4 years ago in reply to user5959213

TI__Guru** 109470 points

Hi There,

I don't have a good explanation on this, but I suspect the issue was come from the reference clock. If the ref clock freq can drift to a much lower value, I guess LMX2594 MUXOUT will always LOW.

Clock & timing

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LMX2594: Output of MUXout pin