LMX2485: Output Instability

Yuta Nishie

Part Number: LMX2485

HI,

Could you please reply to the following thread? I am having trouble with this issue and would like to solve it. I would appreciate it if you could reply soon.

https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1670527/lmx2485-output-instability

Best Regards,

Nishie

22 days ago

0 Noel Fung 21 days ago

TI__Guru** 121130 points

Hi There,

Were you saying that you used the Vcc of the VCO as the trigger to the test equipment? You were turning the VCO on/off in order to trigger the test equipment?

Would you try use the LE pin to trigger the test equipment?

0 Daisuke Higa 18 days ago in reply to Noel Fung

Genius 4915 points

Hi Fung-san

https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1670527/lmx2485-output-instability

Why can't you reply to my post?

I don't understand why it is ignored.

Regarding your question, your understanding is correct. It measures the time to stabilize at startup.

What is your intention to control with LE?

Best regards,

Higa

0 Noel Fung 17 days ago in reply to Daisuke Higa

TI__Guru** 121130 points

Hi There,

Open multiple post on the same subject is not recommended, you can reply your post if you did not get a respond.

When measuring the pll/vco lock time, you should keep the loop working and stable, and then program the PLL to change frequency. No one can predict the loop respond if you have the VCO powered down before programming.

0 Daisuke Higa 17 days ago in reply to Noel Fung

Genius 4915 points

Hi Fung-san

I understand.

However, I posted repeatedly, but there was no reply, so I was worried that it might not have been received, so I posted another message.

I will check if the stability problem at startup is affected by the LE control.

Can you judge from the LE waveform?

Best regards,

0 Noel Fung 17 days ago in reply to Daisuke Higa

TI__Guru** 121130 points

Hi There,

LE is one of the programming pins, you can use it to trigger the test equipment.

0 Daisuke Higa 11 hours ago in reply to Noel Fung

Genius 4915 points

Hi Fung-san

Sorry for the delay as it took a long time to get the waveform.

I got the waveform about the timing of VH2 and LE.(Please refer to the "LE signal" tab in the Excel document.)

As the time has passed, I gathered the information in the document for the reminder.

The LE signal was triggered about 500us after the activation of VH2.

How does the triggering of LE relate to the time until the PLL output stabilizes?

The initial inquiry is as follows, please answer.

[Inquiry]
• Why does the frequency fluctuate after it has converged?
• Could you advise how to suppress the fluctuation (within ±5 kHz)?

Best　regards,

LMX2485SQXNOPB_Inquiry_No1.xlsx

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LMX2485: Output Instability