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USB voltage requirements for F5508

TI Lady
Genius 4025 points
Other Parts Discussed in Thread: MSP430F5508

We have selected the MSP430F5508 for use in our design

 

In reviewing the spec, Section 5.3 talks about voltage rails and what is needed to run the part. It appears that USB needs a minimum of 1.5MHz to work, which is available with input voltages down to 1.8V, so from reading all of this it appears that a Vcc = 3.3V should be sufficient to run the part, including the USB interface.

 

Then I stumbled upon Section 5.44, which if I understand this right implies that the USB system needs to be powered by something greater than 3.75V. So at this point I am not sure if we can run with a main rail of 3.3V and have the USB operational. We do not have any voltage rail greater than 3.3V in our system today.

 

Maybe there is a different configuration for running USB with only low voltage rails present? Please advise.

Thank you so much

  • 0
    TI__Guru 56685 points

    TI Lady,

    The USB Host provides 5V power on the VBUS line. Your system and the MSP430 do not provide this. As a reminder, MSP430 USB is slave only and cannot be host.  Please see the following application note that gives a great explanation on MSP430 USB along with a reference design for HW.

    Regards,

    JH

  • 0
    Guru 33653 points

    There is internal reg inside MSP430F550x with USB (host) 5V input and 3.3V output with few mA, enough to power MSP chip. USB hardware module request at least 1.5 MHz at XT2, but this is not related to MCLK (or any other clock) or Vcc voltage. MSP430F550x with USB hardware module enabled, can work from 1.8V to 3.7V Vcc without any problems.

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