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TPD6E004: ESD Discharge path

ARUN P S
Prodigy 30 points
Part Number: TPD6E004

Tool/software:

Hello Team,

I am developing a signal switching circuit for my use case with a control unit. 

Please find below the supply diagram of my PCB

The shield of the USB and the Ethernet (in MSP432) is connected to the Chassis Ground and the ESD protection diodes are placed near to the connector. 

The input supply is referring to DGND and also there is an isolated power supply in our circuit referring to GND_ISO.

The above shown PCB will be connected to carrier PCB also.

1. Where should the ESD diodes be placed, since this PCB will be connected to Carrier PCB.(On control PCB or Carrier PCB)

2. Any Electrostatics in the connector should be bypassed through the ESD diodes. To which ground the ESD diode has to be connected - DGND/GND_ISO or Chassis GND?

3. Since ESD diodes are connected to the same chassis ground will the isolation get affected?

Could you please support here on this queries

 

  • 0
    TI__Expert 8400 points

    Hi Arun, 

    Please see answers to your questions below:

    1) The ideal ESD diode placement would be as close to the connector as possible. If the connector is on the control PCB then would recommend placing the diode on that board, and if the connector is on the Carrier PCB then place it on that board. It may be too robust, but if there is a concern of ESD entering between the two boards, then you can place ESD on both PCBs. 

    2) Chassis GND is the recommended ground to use. The following is an excerpt from one of our documents:

    "Having a chassis ground for the TVS that is separated from the digital and/or analog ground by inductance provides very good protection against ESD related failures. Yet it presents great challenges when routing high speed circuits across multiple ground planes. For this reason, many designs use one common ground for the protected circuits... Electrical connections to an earth grounded chassis, like a PCB grounded through-hole for a chassis screw, immediately adjacent to the TVS ground and the ESD Source's ground (for example, a connector shield) provide a sound methodology in keeping ground shifts at Protected ICs to a minimum."

    3) I believe the isolation should not get affected by this. 

    Please let me know if you have additional questions or comments. Also, this is a link to a similar thread that might be useful. 

    Best,

    McKenzie