Input protection for i.MX6S USB OTG

[markusbraitner]

Hello,

I got a question concerning the input protection of the i.MX6S USB OTG Interface:

How do I determine the clamp voltage needed for TVS diodes selection as ESD protection?

From 16115_IMX6SDLCEC.pdf, I can see from the absolute Maximum Ratings:

- USB VBUS => 5.25V

- USB_OTG_DP, USB_OTG_DN => -0.3 to 3.63V

- Vesd => 2000V (HBM) / 500V (CDM)

For the Saber Board schematics 27417 I can see that you used a SRV05-4 component for this reason, which has a clamp voltage of 12.5V @ 1A / 17.5V @ 5A. So how to determine the needed clamp voltage if I have to use some other component?

Also, how can I find some Information on the internal Input protection of the i.MX6 in general for figuring out which diodes I need for clamping non-ESD overvoltage on the input?

Kind regards,

Markus

[weidong_sun]

Hello Markus,

About ESD protection:

(1) Considering CPU pin's rating, at first

About rating, see datasheet of i.MX6,please! all pins has been listed in it.

(2)Selecting ESD parts according to Pin's rating.

There are 2 the most important parameters we must focus on :

-----Reverse stand-off voltage : At the voltage, ESD doesn't work.

-----Reverse broken down voltage :After this voltage is exceeded, the diode is rapidly reversed and enters the conduction state.

(3)About Clamping Voltage

:After this voltage is exceeded, the diode will be damaged. The parameter is only related to ESD part, running environment of hardware and max surge voltage, no relations with CPU pin.

Have a great day,
(Weidong)

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[markusbraitner]

Hello Wigros/Weidong,

thank you for your answer! Howevery, it didn't answer my questions...

1) How to determine the needed clamp voltage of the TVS Diode?

If the i.MX6 has an Vesd of 2000V (HBM) or 500V (CDM) (according to the data sheet), I guess I do need a TVS Diode only for higher ESD voltages, did I Interpret that Parameter correctly? By the way, is there somewhere more documentation on this datasheet Parameter?

As written above I have seen that for the Saber design from NXP/Freescale, a TVS Diode with a clamp voltage of 12.5V @ 1A / 17.5V @ 5A has been used, which is significantly higher than the Maximum input voltage for USB_OTG_DP and  USB_OTG_DN which is -0.3 to 3.63V. So how to find out which clamp voltage U_V is sufficient?

Or did I interpret the datasheet wrongly?

2) How can I find some Information on the internal Input protection of the i.MX6 in General?

Maybe this also helps for selecting the protection diodes for small constant voltages (being greater than the absolute Maximum Rating specified for the pin).

Kind regards,

Markus