LMH1218: Writing to registers unpublished on the data sheet.

Dave Pelletier

Part Number: LMH1218

Hi,

I was able to fine tune the LMH1218 used in a fiber optic application in one of our products. The configuration was created by using the SigCon Architect app from TI and also writing to registers that are not published on the data sheet for the LMH1218. Can someone at TI review the register writes I am proposing to our firmware developement team to verify that they are legitimate requirements and won't cause issues with the reliability and long term acquisition of futue manufacturing lots of these devices please? Here is the configuration file saved by SigCaon Architect:

New_Set_Values_HEO_Adj.cfg

Thank You!!

1 month ago

0 David (ASIC) Liu 1 month ago

TI__Guru**** 192831 points

Hi,

Any chance you can highlight the registers you are changing that are not published in the datasheet?

Thanks

David

0 Dave Pelletier 1 month ago

Prodigy 10 points

Hi David,

Thanks for the timely response! The registers not on the data sheet are: 0x9B and 0x9C, which are both now set to 0x01.

Thanks,

Dave

0 Dave Pelletier 1 month ago in reply to David (ASIC) Liu

Prodigy 10 points

Also, another register is written that change reserved bits as labeled on the data sheet. e.g.VEO_Scale, 0x2C set to 0x00. Is this a problem? Again, these registers were configured automatically by the high level programming section of SigCon Architect.

0 David (ASIC) Liu 1 month ago in reply to Dave Pelletier

TI__Guru**** 192831 points

Dave

You can change reg 0x9B and 0x9C both to a lower value like 0x01(default = 0x04). This typically tightens the CDR loop filter bandwidth and reduces the output jitter.

Thanks

David

+1 David (ASIC) Liu 1 month ago in reply to David (ASIC) Liu

TI__Guru**** 192831 points

Dave

VEO is part of the eye monitoring, I also do not see an issue of changing its scale.

Thanks

David

0 Dave Pelletier 1 month ago in reply to David (ASIC) Liu

Prodigy 10 points

Great! Thanks for validating this for me!! Much appreciated!

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LMH1218: Writing to registers unpublished on the data sheet.