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MSP432E401Y: USB Unstable

Tejas s j
Intellectual 425 points

Part Number: MSP432E401Y

Using MSP432E401Y as a USB CDC device. I'm using USB Type-B conenctor (4-pin). 

PB1 is connected to USB 5V using 100E resistor. 

PB0 is left floating. 

 

Observations: 

The USB streaming stops when I connect a sensor to 5V supply. I'm monitoring the USB voltage rails in oscilloscope, there is no drop in voltage or spikes. But still the USB stremaing stops. 

Should I use PB0 and connect to GND or USB 5V? 
Please suggest. 

 

Thank you.

  • 0
    TI__Prodigy 360 points

    Hi Tejas,

    For a Type-B CDC device that does not use OTG, PB0 should not be left floating and can be tied to a defined state such as GND.
    Based on your observation, our first suspicion would be a power-supply issue. When the sensor is powered, it may draw a startup current that briefly disturbs the MCU's local 3.3 V supply, even if the USB 5 V rail still looks stable on the oscilloscope. We can check the 3.3 V rail directly at the MCU when the sensor is powered. If any voltage dip or noise is observed, try adding local decoupling and bulk capacitors near the MCU and sensor, or temporarily powering the sensor from a separate supply to see whether the problem disappears.
    Thanks!
    Ella Tang