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TPD1E10B09: MicoUSB outercasing in TI reference design in not grounded, ESD protection

TapasXplore
Expert 1280 points
Part Number: TPD1E10B09
Other Parts Discussed in Thread: STRIKE, MSP430FR2433

Hi,

I am planning to use TVS diode TPD1E10B09 for ESD surge protection. The general convention is outer edge of the microUSB is connected to the ground, so any ESD strike happens it will be grounded. But in the TI  MSP432P401R SimpleLink Microcontroller LaunchPad Development Kit schematic (USB interface and power supply section), the outer casing of the USB is not grounded. (pic attached). 

1) Will it not make more sense to attach outer casing to ground, what is the significance of attaching it to 33 ohm resistor and then giving it to TVS diode. If VBus has to be given to the TVS diode,  then what is the           need of connecting 33 ohm resistor to the ground?

2) I am studying another reference diagram from TI (MSP430FR2433 LaunchPad™ Development Kit (MSP‑EXP430FR2433)), in this USB interface and power supply section, 33K ohm resistor is connected from             microUSB casing to ground. 

3) Why 180 ohm resistor is being used in the path of VBus and the supply IC. They could be connected directly, what is the significance if attaching 180 resistor in the path of the VBus. 

Regards,

Tapas

  • 0
    TI__Genius 12410 points
    Tapas,
    I believe the 33Ohm resistor is to make sure the ground stays more consistent than the shield so there are less disturbances to the ground plane. The shield is way more prone to be discharged onto than the GND pin itself.
    The L103 is not a resistor it is a ferrite bead that works as an inductor to filter out noise on the Vbus pin. They are very common on power inputs.
    Regards,
    Cameron