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See attched,there are 2 products, Product A and Sensor Product, i want to connect TVS for ESD Protection at +VDC_PWR at one side and where i need to connect the other side to Chassis GND or Soft GND ?
It is better to connect TVS diode to CHASSIS. Chassis ground is preferred since it keeps unwanted ESD transient (and also lightning strikes) remnants out of the circuit that is used by the circuits.
Additionally, Having a chassis ground for the TVS that is separated from the analog ground by inductance provides very good protection against ESD related failures.
It is better to add a inductor or ferrite bead between Soft GND and Chassis GND . By doing this, we can increase protection against ESD related failures of ICs.
1. You can connect the TVS diode to the chassis on sensor block.
2. In product A:
The signal grounds of the Analog circuits are not allowed to be connected to the chassis, which depends on the system architecture, a combination of resistor (1Mohm) and capacitor (xx nF) (even with diode) are used to prevent ground loops as well as parasitic feedbacks between the circuit and the chassis.
The rational behind the value of 2.7kOhm may be specific compliance with any Standard requirements (for Eg CE).
If the soft ground and the chassis are shorted to make it absolutely safe, we may have a ground loop. This may cause performance problems. To minimize the ground
loop current, they suggested to use a 2.7kohm ( I hope that the value arrived based on the analysis on physical system) resistor to connect grounds together. This reduces ground currents to virtually eliminate them.
1. You can connect the TVS diode to the chassis on sensor block.
2. In product A:
The signal grounds of the Analog circuits are not allowed to be connected to the chassis, which depends on the system architecture, a combination of resistor (1Mohm) and capacitor (xx nF) (even with diode) are used to prevent ground loops as well as parasitic feedbacks between the circuit and the chassis.
The rational behind the value of 2.7kOhm may be specific compliance with any Standard requirements (for Eg CE).
If the soft ground and the chassis are shorted to make it absolutely safe, we may have a ground loop. This may cause performance problems. To minimize the ground
loop current, they suggested to use a 2.7kohm ( I hope that the value arrived based on the analysis on physical system) resistor to connect grounds together. This reduces ground currents to virtually eliminate them.
ESD protection should be given to individual product at the entry point of signal.
In your block diagram - sensor section (Considered as separate PCB), the TVS diode is connected to Net '+VDC_PWR'. As per comment #2, the other end of the TVS diode is to be connected to chassis. I hope the Net '+VDC_PWR' is the only entry point to the sensor block (as per your diagram). If there is any other interfaces/IOs, they should be protected through TVS diode.
If this is the configuration, there is no dependency on 'Product A' for 'Sensor block' ESD protection.
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