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Original question:

TCAN1043G-Q1: input capacitance to gnd measurement setup and process

TCAN1043G-Q1: input capacitance

Dongbao Zhou
Expert 4170 points
Part Number: TCAN1043G-Q1

hi team,

i have serval following-up question regarding previous post.

1. Is there any typo in ISO11898-2 as well as last post's description, connect CANL to gnd will take the cdiff into consideration? I think the right Cin measure should connect CANL to CANH, then  . May you double confirm?

2. For Cin test, as OEM requires ECU level test, do we need to remove the termination network--33ohm*2+4.7nF (CMC exclude already)? I am afraid we might not pass the test with termination, pls help confirm?

Regards,

Dongbao

  • +1
    TI__Guru 53555 points

    Hi Dongbao,

    1. When one of the CAN lines is grounded, the measured capacitance (C1) will be Cinput + Cdiff because these capacitances will be put in parallel with ground. The test can be repeated with CANH and CANL shorted to measure (C2) 2xCinput with no component of Cdiff because of the short. With these two capacitance measurements, Cinput can be found as (C2) / 2. The differential component can then be found by subtraction: Cdiff = (C1) - Cinput.

    2. Yes, the termination resistors and common-mode capacitor should be removed for this testing. For the measurement of (C2), this is not required as the two CAN lines being shorted together will short out the termination resistors. They will need to be removed for the (C1) measurement as this would provide an extra current path to GND (CANL shorted to GND). 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    TI__Expert 4170 points

    Hi Eric,

    If you refer to iso11898-2 statement, the Cdiff=(C1-Cin)/2, this really confuses me.

    Dongbao

  • 0 in reply to Eric Schott1
    TI__Expert 4170 points

    Can you send the materials of how do you conduct the test? Like how to take injection frequency/internal and external resistance into consideration that you mentioned in another post, the iso11898-2 looks out of date with errors.

  • 0 in reply to Dongbao Zhou
    TI__Guru 53555 points

    Hi Dongba,

    The current version of ISO11898-2:2016 does not include requirements for input capacitance. The older version has an outdated measurement method that did indeed contain some errors. There has not been consensus between OEMs what the proper method for measuring pin capacitance is, but I will share a document via email that describes a common method that we favor at TI.

    Regards,
    Eric Schott