DP83640 - Surge immunity test LV3(2.0kV)

Hi Ross san,

Thank you for your reply.
We think the same thing, so we will confirm to our customer.

And then, how about our question?
If you have some comment, could you let know us?

Kind regards,

Hirotaka Matsumoto

Ross san,

We appreciate your prompt reply!

It is unbelievable, but our customer claimed  that  before surge immunity test, it is possible to transmit data.
After surge immunity test(LV3), it was not possible to transmit data( being sent or received).
So, after that, our customer changed Etherphy, it is possible to transmit data( being sent or received) again.
As the result of analysis(curve tracer), Etherphy was broken(at pin RD+ or RD-,,, ) by Over Voltage Stress,
our customer suspected that this caused of surge immunity test.


However,  thanks to your update,  we're sure that there is the problem of the circuit.
At the first, we will confirm whether our customer's circuit connects the center tap of the transformer or not.

Kind regards,

Hirotaka Matsumoto

Hi Ross san,

We have some additional questions.
So, could you let know us followings?

<Question1>
Why is "CENTER TAP IS PULLED TO VDD" required?
-It means TP-: GND, TD+ :+6.6V.
-Wtih CENTER TAP conneting to +3.3V, it is possible to remain equilibrium state of the pulse-trans.

<Question2>
If RD- pin is broken by over voltage stress(short mode), dose TD- has the same damage(short mode or leak)?
RD- and TD- are devided on each pins, but we think the Auto-MDIX of the device connects together.
Is our above recognition correct?

We need your help.

Kind regards,

Hirotaka Matsumoto

Hi Hirotaka,

Just for clarification, the surge immunity test is level 3 IEC?

Here are answers to you questions:

<Question1>
Why is "CENTER TAP IS PULLED TO VDD" required?
-It means TP-: GND, TD+ :+6.6V.
-Wtih CENTER TAP conneting to +3.3V, it is possible to remain equilibrium state of the pulse-trans.

Center tap is pulled to VDD since the driver we use is a current mode driver. If it were a voltage mode driver we would have center tap to GND. Since the transformer isolated the ground planes between the link partners, we can use either type.

<Question2>
If RD- pin is broken by over voltage stress(short mode), dose TD- has the same damage(short mode or leak)?
RD- and TD- are devided on each pins, but we think the Auto-MDIX of the device connects together.
Is our above recognition correct?

I believe your assumption is correct. Because of the Auto-MDIX, there is the possibility of the stress applied to RD- also stressing TD-. 

Keep me updated on what your customer finds when they connect the center tap properly.

Kind Regards,

Ross

Ross san,

Thank you for your prompt update and your ccoperation!

We heard that the surge immunity test is LV3 IEC61000-4-5.
And then, we could found they don't connect the center tap properly.

Kind regards,

Hirotaka Matsumoto

Hi Hirotaka,

I will ask the design team about the IEC spec. From what I know is that the device was tested using the HBM. I will check with them what the limits are with IEC. 

Regards,

Ross

Ross san,

Thank you for your help!
We are looking forward to your reply.

Kind regards,

Hirotaka Matsumoto

Hi Hirotaka,

Here is an app note for IEC. It lists at the end various tests on the device and finding/ways to mitigate errors.

Please let me know if your customer still sees errors after connecting the transformer correctly.

http://www.ti.com/lit/an/snla108a/snla108a.pdf

Kind Regards,

Ross

Ross san,

Thank you for your help!

OK, we will confirm our cutomer, and will inform you the result.

Kind regards,

Hirotaka Matsumoto