DS90UB948-Q1: Display shift when ESD air discharge

Hi Daniel,

If the customer has isolated the screen shifting issue to the 948 PATGEN, then this ESD behavior is most likely a systematic issue. Where in the system is the air discharge being done?

The oLDI protocol has no provision for error checking on a line or frame level. The most relevant registers that we typically recommend for improving ESD performance are 948 Register 0x41. 

Below are some previous E2Es on 948 ESD performance with for your reference.

https://e2e.ti.com/support/interface-group/interface---internal/f/interface---internal-forum/1453316/ds90ub948-q1-link-error-count-register-under-esd-test?tisearch=e2e-sitesearch&keymatch=ds90u%252525252A94%252525252A%2525252520AND%2525252520ESD#

https://e2e.ti.com/support/interface-group/interface---internal/f/interface---internal-forum/1462989/ds90ub948-q1-improve-esd-performance-by-changing-0x41-register

Best,

Jack

Hi Jack

Air discharge was done on the panel(with cover glass), and the picture shift will occur even  air discharge was done GND.

Did you meet the similar issue before？

Could you give me some advices？ Thank you.

Hi Zhuang,

Do you have a video of the ESD behavior? Is this is a temporary screen shift during the ESD event? Does it self-recover?

FCE Zhuang said:

Air discharge was done on the panel(with cover glass), and the picture shift will occur even  air discharge was done GND.

By "picture shift will occur even air discharge was done GND", I assume you mean that the air discharge on the board GND still causes the screen shifting behavior.

The most effective way to ensure system level ESD performance is to ensure that from the hardware design the housing, shielding, and grounding of the board are all designed to shunt energy away from the high-speed signals. ESD can also affect the power rails to the device.

A ground ring around the PCB and ESD diodes can help to shunt ESD energy away from sensitive parts of the PCB. I have posted some relevant E2Es below.

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/888357/ds90ub941as-q1-esd-contact-discharge-test-fail-8kv

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/958162/ds90ub914q-q1-camera-frame-broken-bouncing-happen-during-8kv-contact-discharge-esd

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/931130/ds90ub947-q1-how-to-pass-8kv-contact-discharge

Best,

Jack

Here is the video for reference.

By "picture shift will occur even air discharge was done GND", I assume you mean that the air discharge on the board GND still causes the screen shifting behavior.

->Yes, you are right.

 Since the phenomenon is same when enable the pattern of 948, I think the output OLDI signal was influenced, and I think we can't add ESD diodes at OLDI signal. 

We also have big ground ring around the PCB edge .

If you have any other advices, I would highly appreciate it.

Hi Zhuang,

I'll be following up shortly.

Best,

Jack

Hi Zhuang,

I don't know the complete background of this system so I need to ask some questions.

• What is the serializer?
• Is this coax or STP?
• Is this single FPD-Link or dual FPD-Link?

You and Daniel have stated that the screen shifting behavior was seen with 948 PATGEN as well. How did you program the PATGEN? Were you using internal or external timing? 

There are three main possibilities for why the screen is disrupted during an ESD event

• Loss of lock
• 948 voltage rails brownout
• Excessive noise on OLDI traces

To monitor for potential loss of lock, register dumps of the SER and DES can be taken before and after the ESD event. Both the "948 voltage rails brownout" and "excessive noise on OLDI traces" would require measurements. Figuring out why ESD is causing the screen disruption will be the best way to stop this behavior.

If you are able to send over the schematic and layout, it would help me understand any potential spots in the display unit that are more susceptible to ESD. Since this is a public forum, you can send the schematic and layout to me over email (j-scherlag@ti.com).