SN65C3243: Malfunction due to ESD(2kV).

Kengo,

In both DOUT waveforms, after the 2kV strike it looks like a leakage path has been created to GND causing the output to be attenuated. And for the RIN and ROUT connections, the signal doesn't look attenuated but there seems to be no propagation from input to output. Is this happening on all RIN, ROUT, DIN, and DOUT pins?

Regards,

Eric Hackett 

Eric,

Thank you for your reply.

All the pins they are using will occur.
However, it is unused except for the four pins with waveforms(as my attached).

Sincerely.
Kengo.

Kengo,

What kind of 2kV ESD strike are you referring to? Is this IEC ESD testing?

Regards,

Eric Hackett

Eric,

Since we hit ESD on the chassis, we do not know the intrusion route of ESD.
This test does not comply with the IEC testing.

Sincerely.
Kengo.

Kengo,

Understood, do you know which coupling network was used? This is the resistor + capacitor value combination used to generate the ESD strike. I ask because this device is only rated for HBM strikes, so protection would be needed otherwise. What VCC supply voltage are you using?

Since this is affecting every single port on the device, is it possible to measure the supply voltages, V+ and V- when the board is powered on, and also check to see if there are low impedance paths to GND on FORCEON and FORCEOFF?

Regards,

Eric Hackett

Eric,

Thank you for your reply.
We have to take some measures against this ESD strike.

>What VCC supply voltage are you using?
 -> VCC is 3.3V

>is it possible to measure the supply voltages, V+ and V- when the board is powered on, and also check to see if there are low impedance paths to GND on FORCEON and FORCEOFF?
 -> Could you tell me how to measure your advice?
     This phenomenon only occurs when ESD is applied.
     It recovers when the power is turned off.

Sincerely.
Kengo.

Kengo,

Oh okay, this makes this a much different phenomenon, so there is no damage present after a power cycle. I'm curious if this is messing up the charge pump circuits after the ESD strike. Is it possible to measure with an oscilloscope or multimeter after an ESD strike has been applied and before power is turned off?

Regards,

Eric Hackett 

Eric,

Thank you for your comment.
I'll check with my customer to get waveform at V+/-pin after ESD strike.

 Sincerely.
Kengo.

Hi Eric,

The voltage of the charge pump circuit has changed.
Could you pls tell me where to take measures?


Sincerely.
Kengo.

Kengo,

Thanks for this, that confirms that the strikes are coupling into the charge pump circuit and causing issues. Can you also check the FORCEON and FORCEOFF pins after the strike? I want to understand why the RIN and ROUT signals aren't responding at all, and I'm wondering if FORCEOFF is getting triggered for some reason. Along with that, can the ROUT2B pin be tested after the strike as well?

Thank you and the customer for getting all this data. If all of these pins are affected (charge pump, FORCEOFF) it may be a ground bounce from the ESD strike that causes some kind leakage paths/latch states and only returns back to normal when the part gets powered down and all the internal circuits gets discharged.

Regards,

Eric Hackett

Eric,

I attached the waveform.


No change was seen.
However, Rout2B is not use, so it was OPEN.

Sincerely.
Kengo.

Kengo,

Was data driven to the ROUT2B port? This pin is supposed to work despite the state of FORCEOFF and FORCEON, and I want to see if it works when the rest of the ROUT pins are not passing data. My thinking is if ROUT pins are not working, maybe the state of FORCEOFF is going low. But looking at the waveform, FORCEOFF is still high. I'd still like to see if data can pass through ROUT2B after the ESD Strike though.

Given your last post showing the charge pump circuits with lower voltages, it's clear they are getting affected by the ESD strike. Adding filtering to VCC in the form of capacitors may help, but in general this will be difficult to diagnose where the strike is traveling. Again, since all of the Din and Dou and Rin and Rout pins are being affected, to me this points to the charge pump and/or VCC pins.

Regards,

Eric Hackett 

Eric,

Thank you for your comment.
I attached the waveform.


Sincerely.
Kengo.

Hi Kengo,

Thanks for sharing. We'll get back to you with more information on Tuesday (long weekend in the US).

Regards,
Eric Schott

Hi Eric,

Thank you for your reply.
I'll wait for your come back.

Have a nice long weekend!

Sincerely.
Kengo.

Hi Kengo,

Is it possible to share a schematic of the RS-232 circuit on this board? Please include decoupling, and charge pump capacitor values. We'll make sure all of these are valid and suggest changes if we believe we could improve performance in any of these spaces. In the meantime, I would recommend testing with a larger decoupling capacitance to try to filter out the ground bounce Eric H mentioned. If the no bulk capacitance is already in place, I would recommend starting at 10uF and increasing from there. 

Regards,
Eric Schott

Hi Schott,

Thank you so much for your advice.
I'll attach a schematic.
If you have any comments below, pls let me know.



Sincerely.
Kengo.

Hi Kengo,

Thanks for sharing. All the charge pump capacitor values look good. 

Is there any bulk capacitance on the board? If so, have you trying varying the amount of this in the testing? Having a larger bulk capacitance will help stabilize the power lines during ground bounce. 

Regards,
Eric Schott