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ADS1220EVM not enumerating USB when powered via external 5V

Jason Taschereau
Prodigy 140 points
Other Parts Discussed in Thread: ADS1220

When jumper JP7 is open, an external supply voltage (+5V) can be fed in to connector J7 to power the module. When I do this, the module never enumerates as a USB device once plugged into a PC. If JP7 is shorted and no external voltage is supplied through J7, however, the module powers up from the USB +5V and then enumerates properly.


It feels like I'm missing something really obvious here... any help would be appreciated!

  • 0
    TI__Guru** 113765 points

    Hi Jason,

    Welcome to the forum!  This is a very odd behavior.  I have the same result.  I will have to investigate this further.  I believe this has something to do with internal timing within the MSP430.  If I find something I will let you know.

    Here is something else you can try.  As the EVM will only support 5V for the AVDD supply, you could leave the JP7 connector in the default position which will allow the EVM to enumerate.  You can then apply +5V to the AVDD supply by removing AVDD supply jumper JP3 and connecting the external supply to the common connected pins of JP3 (pin 1 or pin 3 of the header).  The GND connection can be applied at one of the GND testpoints or the GND connection on J7.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Guru** 113765 points

    Hi Jason,

    The problem with enumeration involves the timing and noise on the voltage supplied from USB to the MSP430.  With JP7 there is adequate capacitance to maintain the necessary charge.  When JP7 is removed there is no bypassing or charge reservoir on the VBUS pin of the MSP430.  Every time the device tries to enumerate, charge is demanded through the L1 ferrite which eventually places the device into a brownout condition and restarts the USB connection on the MSP430.  The enumeration never completes.

    I resolved this issue by soldering a capacitor to the bottom side of the EVM between the JP7 connection of the USB supplied voltage and the ground terminal of J7.  I used 47uF (as that is what I had handy), but 10uF should also work as that is similar to the normal capacitance when JP7 is installed.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 140 points

    Thanks for the quick replies!


    I think your first suggestion to power the 3.3V regulator off the USB with JP7 shorted, then hook in my external +5V to the AVDD common side of JP3 will accomplish what I needed. I just needed to verify if there was any difference in my measurements when the ADS1220 was powered from the same 5V supply as my drive circuit, or powered from the USB.


    -Jason