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TUSB217A: Changing VCC from 5V to 3.3V on Existing Design

Brian Gosselin
Expert 4745 points
Part Number: TUSB217A

Tool/software:

Hello,

My customer is using the TUSB217A with VCC = 5V (VBUS, same supply as the USB device they're testing).  Do you expect any changes to the device behavior/performance if they move to a 3.3V supply?

My thoughts based on the datasheet:

The TUSB217A supports 3.3V (2.3-6.5V), but it does appear that some specifications are dependent on VCC.  For ex., VIL and VIH(min) for Input RX_SEN (pg. 7 of DS).

I see in Table 9-1 that the 37.5kohm resistor is required for a 5V supply to divide the voltage down so the RX_SEN pin voltage does not exceed 5V.  It appears this resistor is not needed for 3.3V supply.

They may want to review their BOOST setting to confirm it’s optimized after switching to 3.3V VCC.

Do you agree?  Anything else we should highlight?

Best Regards,
Brian

  • +1
    TI__Mastermind 37480 points

    Hi Brian,

    That's correct, one thing that would need to be checked is the inputs for the RX_SEN pin. With a 3.3V VCC, the RX_SEN pin would require 2.475V minimum to detecting a high-level signal. Using the resistor settings recommended for RX_SEN at 5V would put the voltage exactly at 2.475V with a 3.3V VCC, so they could still be used if the customer wanted. Otherwise, we recommend just a 22-40KOhm resistor pulling the pin up.

    Brian Gosselin said:
    They may want to review their BOOST setting to confirm it’s optimized after switching to 3.3V VCC.

    For the BOOST pin, this pin is not affected by a lower VCC. The resistors currently used on for this pin at 5V VCC can also be used for 3.3V.

    Brian Gosselin said:
    Do you expect any changes to the device behavior/performance if they move to a 3.3V supply?

    Other than needing to review the RX_SEN pin, I don't believe they should expect any change in performance.

    The only other thing I would recommend checking, if its being used, is the pull-ups on the I2C lines. Otherwise, I don't have any other input.

    Thanks,

    Ryan