DSI DISPLAY DOES NOT WORK AFTER ESD EVENT

[DKUMA.11]

Hi,

I have working on STM32MP157C-DK2 Board and after application of 8KV ESD strike on USB Shield, the DSI Screen Goes off completely (Discharging on Ground only). 

To verify the issue I have applied the same strike on a custom board consisting of STM32MP157CAC3 and SN65DSI83 to display video out. Same thing happening. After little bit of probing I found that DSI clock is working fine and Data lines are also toggling but there are lots of EOT,ECC errors.

In this case if I set the MPU to sleep mode using command " echo mem /sys/power/state " and then wake using PMIC Wake Key Press then the DSI signal again start working perfectly and ECC and EOT error goes off.

What could be the reason for this behavior? How can I solve this. 

We are waiting for mass production of our device just because of this issue as the ESD testing is failing.

Kindly help us solving this issue.

Kernel : 5.10.10

Yocto Build : Dunfell

[TDK]

> 8KV ESD strike

That's a huge ESD event.

Likely going to need to add ESD protection to your board if you want protection above and beyond what's in the datasheets. I didn't look at the display, but the STM32MP chip itself only protects up to 2kV (HBM).

[RhSilicon]

R.I.P.

[DKUMA.11]

Hi 

The board is fully protected with TVS diode don't worry.

We have already used 30KV and 15KV TVS in the line wherever required in our custom board. The DK2 board also has ESD protection. Not just at 10KV, we are facing this issue at 4KV as well.

By the way, the standard requires 15KV air and 8KV Contact discharge rating on device.

[DKUMA.11]

kindly provide some useful insights. This will be helpful.

[DKUMA.11]

System is working fine after reboot:face_savoring_food:

[RhSilicon]

I did a similar test (in 2011/2012) with some PIC16F (Microchip), LM555 and ATmega32 (ATMEL before being bought by Microchip). Approaching a large relay (contactor) in auto oscillation, to generate electromagnetic noise. Only the ATmega managed to keep running, the others restarted randomly.

[PatrickF]

HI @DKUMA.11 

I'm not ESD expert, but I can say that we guarantee the following ESD (IC product) values:

The IC Datasheet specify both:

• IC ESD sensitivity (i.e. device could not behave correctly above this value, but resume after a reset/power cycle)
  
• IC ESD absolute rating (i.e. device could be damaged above this value)
  

Note that the STM32MP157x-DK2 board is a development board and might not be designed to fit specific environmental requirements.

I think resistance to ESD strikes on a product should includes casing, shielding as well as power supply routing/decoupling or other sensitive signal isolation/decoupling/filtering.
TVS or similar component are mostly for protecting the device to be damaged, but does not avoid energy flow thru supply/ground. Careful system design analysis might be needed (usually involves customer experience in their product field area).

In your case, maybe worth to focus on current paths used during strikes, there could be something to enhance on PCB ground layer or more direct path to ground (e.g. direct connector ground to metal casing/shielding).

Then, as a mitigation, you should also find a way to detect the misbehavior and issue a watchdog reset.

Regards.