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Original question:

DS99R103: DS99R103/104 vs DS99R105/106

DS99R103: Can DS99R103 be used interchageably with DS99R105 if pre-emphasis is disabled via pull-up resistor?

Sarah Rosenstein
Prodigy 30 points
Part Number: DS99R103


Hi, 

I understand the differences between DS99R103/104 and DS99R105/106 are the temperature ratings and ways to configure the pre-emphasis pin. My question is about interchangeability if pre-emphasis is disabled.

For DS99R105, pre-emphasis is disabled by pulling the pin high (enabled by pulling it low).

For DS99R103, pre-emphasis is disabled by leaving the pin floating (enabled variably by different value pull-down resistors.)

If a design currently uses DS99R105 with a pull-up resistor to disable pre-emphasis, can the DS99R103 be used interchangeably, where the pull-up R will not draw current from the internal current source? or does the pull-up resistor need to be removed and the pin must be left floating for pre-emphasis to be disabled with DS99R103?

Thank you,

Sarah  

  • 0
    TI__Expert 3595 points

    Hey Sarah,

    I suggest removing the pull-up resistor and leaving the pin floating for the DS99R103.

    Let me know if you have any further questions!

    Thanks,

    Lysny

  • 0 in reply to Lysny Woodahl
    Prodigy 30 points

    Hi Lysny,

    Thanks for the suggestion, I am hoping for a definitive answer to my question: is it necessary to remove it? Will it be an issue if it is left in place? 

    The reason I ask if it is required to remove it is that it means more changes on the production line, where the hope is that no changes would be necessary, just populating DS99R105 or DS99R103 with no other BOM changes. 

    If you cannot give a definitive answer, I will take it to mean the resistor must be removed for proper operation. 

    Thank you!

    Sarah

  • 0 in reply to Sarah Rosenstein
    TI__Expert 3595 points

    Hey Sarah,

    For now, the resistor must be removed for proper operation. 

    These are older products meaning that we do not have access to all the design materials. I will look into this though and see if I can get a confirmation.

    Thanks,

    Lysny

  • 0 in reply to Lysny Woodahl
    TI__Guru** 103215 points

    Sarah,

    The resistor should be removed for DS99R103. These two parts actually do have a different internal connection for this circuit. In the R105 part the internal connection of this pin does not go to a current source - instead it is routed to an OR gate. I would not suggest to place a pullup resistor on the R103 part as you will be attaching that directly to a current source. Please remove that for R103 population and leave floating as the datasheet says. 

    Best Regards,

    Casey