LMK03328: LMK03328_unexpected Input REF_LOS indication when reference input is a 25 MHz XTAL input

Richard.JR Chen

Part Number: LMK03328

Hi TI Team,
Here is our LMK03328 schematic.

And the LMK03328 config file as attach. AWS NPO-Test-Platform LMK03328 profile.zip

We are seeing an unexpected SECREF_LOS indication on LMK03328's STATUS0 pin when SECREF is configured as a 25 MHz XTAL input.

Current observations:

* 25 MHz XTAL is oscillating normally (~1.8 Vpp)
* PLL1 is locked. We confirmed this by measuring LMK03328's STATUS1 pin, it is ~0V which means PLL1_LOL is deasserted.
* All 100 MHz outputs of LMK03328 are normal
* However, we see LMK03328's STATUS0 pin is ~1.8V which means that SECREF_LOS is asserted.
* We tested all SECREF detection modes (VIH/VIL, + Slew, - Slew, +/- Slew), but SECREF_LOS remains asserted.

Could you please confirm whether SECREF_LOS is supported in XTAL Input mode? If yes, is there any specific detector/register setting required for XTAL mode?

Thanks for your support.

Best regards,
Richard

19 days ago

0 Sandra Saba 18 days ago

TI__Expert 4850 points

Hi Richard,

I am looking into the issue and will get back to you by early next week with feedback.

Please note that this is a public thread

Best,

Sandra

0 Sandra Saba 18 days ago in reply to Sandra Saba

TI__Expert 4850 points

Hi Richard, i responded to your email.

This may be due to the status pin is active high which inverts the logic. It would be good to check the loss of signal bit as well to confirm.

Best,

Sandra

0 Richard.JR Chen 11 days ago in reply to Sandra Saba

Prodigy 10 points

Hi Sandra,

We found one LMK03328 LOS-related post from TI E2E forum.

LMK03328: Loss of signal status doesn't appear to work - Clock & timing forum - Clock & timing - TI E2E support forums

As Cris Kobierowski replied in this post : The LOS bit does not apply to XTAL inputs.

Because we use the XTAL input for SECREF_P/N, so the SECREF_LOS function is not applicable to our design. Is my understanding correct?

If SECREF_LOS cannot be used in our design, how can we monitor or verify the XTAL input status through software?

The only way to indirectly confirm that the XTAL input is by checking PLL1_LOL?

thanks

Richard

0 Sandra Saba 7 days ago in reply to Richard.JR Chen

TI__Expert 4850 points

Hi Richard,

I'm confirming this with out team internally on XTAL monitorting. I will get back to you end of week with some feedback.

Apologies for the delay

Best,

Sandra

0 Sandra Saba 5 days ago in reply to Sandra Saba

TI__Expert 4850 points

Hi Richard,

Apologies for the delay!

Confirmed with the team internally, LOS signal is only applied when the input reference not XTAL, you can monitor the PLL status if it goes out of lock.

Best,

Sandra