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LMH0318: LMH0318 CDR does NOT lock if SMBus initialization sequence used

Benjamin Kohl
Prodigy 20 points
Part Number: LMH0318
Other Parts Discussed in Thread: LMH0324, DS25CP104A,

Hello,

we have developed a 3G-SDI switch with the following TI components:

Equalizer: LMH0324

Switch: DS25CP104A 

Reclocker/Cable Drive: LMH0318

If I power on the device without  any SMB access to the LMH0318 the LMH0318 CDR locks (LOCK pin signal = H 2.5V) successfully.

Using the following sequence, the CDR does not lock!

RAW FF 04 07 //Select Channel Registers
RAW 16 25 FF //Enable Full Temperature Range
RAW 3E 00 80 //Initialize CDR State Machine Control
RAW 55 02 02
RAW 6A 00 FF
RAW 03 XX FF //Use the desired CTLE settings. See CTLE Test Mode to determine the CTLE
setting
RAW 0A 0C 0C //Reset CDR
RAW 0A 00 0C //Release CDR reset

I tried different CTLE settings, but the result remains the same. The PCB tracks between switch and LMH0318 are short (< 2 inches).

Then I tried only the following access:

write_reg_blocking(dev, 0xFF, 0x04, 0x07); // Set Channel Register

Even with this simple command the LMH0318 lock does not work.

If I remove this remaining SMB access from the firmware then the LMH0318 activates the LOCK signal (after disconnecting and reconnecting the supply voltage).

So I suspect that the SMB access somehow blocks or disables the CDR lock. Do you have any hints?

Thank you.

Best regards

 B.Kohl

  • 0
    TI__Guru* 91400 points

    Hi Benjamin,

    This is very strange since even issuing a single command would cause the device to not lock. 

    Once device is not locked, is there any output signal? Do you see any increase in power consumption? 

    Does the device comes back to normal lock state after issuing this single SMBus command or stays unlocked forever?

    Regards,Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser,

    thanks for the fast response.

    Yes, we have an output signal, and yes the power consumption is increased. It stays unlocked forever until the next power cycle.

    I took a closer look at the SMB implementation and found errors within the Write_Register function. Incorrect data was written to the IC.

    With the corrected firmware, the IC now works as expected (SMB Init successfull and CDR lock active)

    Thanks.

    Best Regards

    Benjamin

  • +1 in reply to Benjamin Kohl
    TI__Guru* 91400 points

    Hi Benjamin,

    Thanks for the update. I was scratching my head trying to see what could be occurring here. 

    Now that you mentioned this, you could be writing into the reserved registers preventing device to lock to the incoming signal.

    Regards,Nasser