• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 33 subscribers
  • Views 361 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TUSB522P: Resd resistor

Zach Kimble
Intellectual 1940 points
Part Number: TUSB522P
Other Parts Discussed in Thread: STRIKE

Hello,

In the datasheet, it mentions in section 8.2.2.1 that a resistor is sometimes suggested on the differential pins to pass IEC 61000-4-2 contact +-8kV. I have two questions about this:

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?

2. The recommended ESD protection device, PUSB3FR4, has a clamping voltage of 3V. In section 8.2.2.1 in the datasheet, it says that Resd may be required if the clamp voltage is greater than 4V. In table 8-2, despite PUSB3FR4 having just 3V clamping voltage, it recommends a 2.2ohm resistor to pass IEC61000-4-2. Why is this resistor recommended here?

Thank you!

Best regards,

Zach Kimble

  • +1
    TI__Mastermind 30700 points

    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

  • 0 in reply to Shane Hauser
    TI__Intellectual 1940 points

    Thank you Shane! This all makes sense. I have no further questions.

  • 0 in reply to Zach Kimble
    TI__Intellectual 1940 points

    Hi Shane,

    After discussing with my team, I have one additional question. Is Resd recommended to pass IEC61000-4-2 contact 4kV testing? Or would the diode alone be good enough for just the 4kV testing?

    Best regards,

    Zach Kimble

  • 0 in reply to Zach Kimble
    TI__Mastermind 30700 points

    Hi Zach,

    That's a good question. I can't find an ESD report for this device at 4kV so I can't say for certain.

    One option you can take is to add 0-ohm resistors on the TX and RX lines. If the ESD test fails at 4kV, you can swap the 0-ohm resistors for 2 ohm resistors. I recommend using size 0201 resistors for this purpose.

    Best,

    Shane

  • 0 in reply to Shane Hauser
    TI__Intellectual 1940 points

    Hi Shane,

    Thank you for the recommendations! I will let the customer know.

    Best regards,

    Zach Kimble

  • +1 in reply to Zach Kimble
    TI__Mastermind 30700 points

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

    Best,

    Shane