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AFE5818: GBL_ACTIVE_TERM and ACT_TERM_IND_RES

TISL
Expert 4630 points
Part Number: AFE5818

Dear e2e Support,

Do we have anymore document, than the datasheet, to explain how to optimize the two registers GBL_ACTIVE_TERM and ACT_TERM_IND_RES?

Can we set both enabled at the same time (meaning we have 3x termination in parallel: 15kohm, GBL and IND)?

Do we have any process/guidelines to optimize this termination settings?

Regards,

  • 0
    TI__Expert 6980 points

    Hello,

    Apologies for the delay in response.

    I looked at the schematic of the device and found that both the registers are not mutually exclusive. Meaning GBL_ACTIVE_TERM will override the ACT_TERM_IND_RES and hence you cannot use both of them together in parallel.

    Either ACT_TERM_IND_RES or GBL_ACTIVE_TERM will work but not both in parallel. 

    you can optimize it from the available selection of values of resistors and you can always put external passive resistor,

    Thanks & regards,

    Abhishek

  • 0 in reply to Abhishek Vishwa1
    Prodigy 20 points

    Hello Abishek,

    Thanks for this answer. I am another TI AFE5818 user with the same question.

    Is there an application note to explain when we should use GBL_ACTIVE_TERM or ACT_TERM_IND_RES ?

    GBL_ACTIVE_TERM have less settings but it looks like it configures automatically ACT_TERM_IND_RES depending on LNA gain to get a fixed termination resistor value.

    On the other side, ACT_TERM_IND_RES looks to have more setting but it needs to be adjusted depending on LNA gain.

    Could you confirm that ?

    Regards,

    Nicolas PERRIN

  • 0 in reply to Nicolas PERRIN
    TI__Expert 6980 points

    Hi Nicolas,

    I am sorry for delayed response as I was on leave.

    We do not have any application note on the usage of active termination. However you are correct, the GBL_ACTIVE_TERM presents fixed input resistance across all LNA Gain, it can be programmed to 50Ω, 100Ω, 200Ω and 400Ω based on the value in Reg198[5:4].

    The ACTIVE_TERM_IND_RES set the active termination resistor value using the LNA gain as well. The equation followed by this setting is :

    R = 20 kΩ / NACTIVE / (1 + GLNA / 2),

    where NACTIVE is the decimal equivalent of the ACT_TERM_IND_PROG setting and GLNA is the LNA gain (in linear units). To enable this control, ensure that ACT_TERM_IND_RES_EN is 1.

    Please let me know if you have any further questions/

    Thank you,

    Abhishek

  • 0 in reply to Abhishek Vishwa1
    Prodigy 20 points

    Hi Abishek,

    Thanks for your answer it is perfectly clear for me now.

    Regards,

    Nicolas