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TCA9517-Q1: Schematic review request

MJ Jeon
Genius 5240 points
Part Number: TCA9517-Q1

Hi, Support Team

Please review the circuit diagram created by the customer.

I have an inquiry about EN among the above circuits.

If you look at the functional block below, an internal pull-up is set.

If I always want to use it in the state of Enable, can the external connection be floating?

 

Thanks.

Regards,

MJ

  • +1
    Guru 244270 points

    Yes; when the EN pin is open, the internal pull-up resistor (about 500 kΩ) prevents it from floating. This is also described in section 9.3.2 of the datasheet.

    If you fear that the pin might pick up noise from an extremely noisy environment, you can connect it directly to VCCB.

  • +1 in reply to Clemens Ladisch
    TI__Guru 60392 points

    Thanks for the help Clemens!

    MJ,

    Clemens is correct, and I've also notified an engineer from TI to get some more eyes on this just in case.

    Regards,

    Eric Hackett

  • +1 in reply to Eric Hackett
    TI__Genius 15345 points

    Hi MJ,

    As Clemens said you can leave it floating and it will stay enabled, however if you are in a noisy environment and never want to disable the device I would recommend using another strong pull up resistor and a capacitor connecting it to the EN pin.

    Here is my schematic review:

    • Pinout on schematic matches pinout on datasheet: Correct
    • Decoupling capacitors included and valued well: For decoupling capacitors we recommend a value of 100 nF. It looks like you are using a value of 10 nF.
    • SDA/SCL net names match pins: Correct
    • Pull up resistors included and valued well: Good on the A side, double check the B side resistors make sure they do not exceed your maximum pull up resistance.

    Make sure that the VOL of any device on the B side is below 0.4 V or that your pull up resistors are sized appropriately to minimize the VOL. 

    Make sure that the device connected to the B side is not another static voltage offset buffer on the offset side.

    The VOL of the B side is pretty high so make sure that any device on the B side has a VIL > 0.6V

    Best,

    Chris