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TIDA-01238: Using of U3 on FET solution

Sayyid Ishaqi
Prodigy 20 points
Part Number: TIDA-01238

Tool/software:

Hello,

To engage the termination resistor on FET solution, only U4 should be turned on by driving its gate to 5 V. Therefore, JMP9 should be connected to VCC and JMP10 to GND (to keep U3 turn off), correct? The purpose of U3 (CSD17483F4T) is to act as a voltage level shifter when using a 3.3 V microcontroller to control U4, and also to provide protection to the microcontroller I/O pin in case of high voltage on the CAN bus, correct?

  • 0
    TI__Guru 51616 points

    Hi Sayyid,

    Yes, the jumper logic is as described where the gates should be connected to VCC to engage the termination or connected to GND, to disengage. 

    By protection, I believe you are referring to the capacitance of the gate and the divider network to ease the load on the MCU. Hence, RC filter / current limiter. However, this is not a surge protection as the MCU pin should mainly see U3's gate as a capacitive node. I.e, CAN bus transients are kept away from the logic path by the transceiver and by U4's channel. The divider's role would mainly be to drive-shape and light level shift / bias, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 20 points

    Hi Michael,

    To activate the termination, only U4 should be connected to VCC while U3 should be connected to GND, correct?
    If we use a 5 V microcontroller, is it possible to completely remove U3 and connect microcontroller I/O directly to U4 to control the engagement?


    Best regards

    Michael,

  • +1 in reply to Sayyid Ishaqi
    TI__Guru 51616 points

    Hi Sayid,

    Yes, your understanding is correct, thanks.

    Best Regards,

    Michael.