Clock & timing

Clock & timing forum

State Resolved
Locked Locked
Replies 7 replies
Subscribers 21 subscribers
Views 398 views
Users 0 members are here

Support feedback

Options

Options

Related

LMX2595EVM: LMX2595EVM

singam vamshi krishna

Intellectual 775 points

Part Number: LMX2595EVM
Other Parts Discussed in Thread: LMX2595

Hi team,

In my application I need to use external reference signal. I have changed the configuration of LMX2595 EVM and tried feeding it with external reference signal. As suggested in EVM manual for single ended external clock I have populated R25 51 ohm with 47 ohm, Will that make any difference in output frequency. I have loaded the register values but the output frequency is shifted by 500 MHz. Should the resistance value be exactly at 51ohm?

Thank you in Advance

over 3 years ago

0 Noel Fung over 3 years ago

TI__Guru** 106770 points

Hi Singam,

That resistor will not alternate the VCO frequency, it will simply make the load as seen by the clock source a little bit off from 50Ω. The result may be a little bit reduction in signal swing, in general, this is not a big deal.

If your output frequency is off by 500MHz, most likely the PLL is not locked. Were you using TICS Pro to control the board?

0 singam vamshi krishna over 3 years ago in reply to Noel Fung

Intellectual 775 points

Yes I am using TICS Pro GUI to control. It has interfaced with Ref Pro board.

0 Noel Fung over 3 years ago in reply to singam vamshi krishna

TI__Guru** 106770 points

Hi Singam,

If you use TICS Pro "Default mode" configuration, can you make it lock?

Before you change the reference clock, did you get it lock with the on-board XO?

0 singam vamshi krishna over 3 years ago in reply to Noel Fung

Intellectual 775 points

Yes, But in default mode also the similar drift appeared at output frequency.

When using internal on chip reference, it is locked and no drift at output frequency.

0 Noel Fung over 3 years ago in reply to singam vamshi krishna

TI__Guru** 106770 points

Hi Singam,

What is your external clock source?

0 singam vamshi krishna over 3 years ago in reply to Noel Fung

Intellectual 775 points

I am making use of Agilent Signal generator, wherein I fed 100 MHz, 8 dBm as input to LMX2595.

+1 Noel Fung over 3 years ago in reply to singam vamshi krishna

TI__Guru** 106770 points

Hi Singam,

A signal generator is good.

Did you remove the power supply of the on-board 100MHz XO?