TUSB522P: Resd resistor

Hi Zach

Zach Kimble said:

1. What does this resistor do? How does it improve the protection for the device if there is already a capacitor to block excess current flow?

You are correct that the capacitor will block DC current from entering our device. In an ESD strike, you will have a spike in voltage that acts more like an AC signal when it first reaches the capacitor. The rapid change in voltage from an ESD strike will pass through that capacitor just like a USB signal would .

Resd is meant to lower the voltage of the strike current that moves through the AC coupling capacitor. By going through Resd, the voltage of the strike that reaches our device will be less than what goes through the capacitor.

Zach Kimble said:

2. Why is this resistor recommended here?

Resd is a recommendation if needed for passing IEC ESD testing.

Having a low clamp diode like PUSB3FR4 will better protect the 522P by clamping sooner when an ESD strike occurs. If your clamp voltage is above 4V, it presents a higher risk of the 522P being damaged. This risk can be mitigated by adding Resd in the signal path.

Best,

Shane

Sounds good. I'll mark this as resolved, but let me know if you need anything else.

Best,

Shane