TMS320C6748: About Errata SPRZ303H Advisory2.3.18

Hello Hiroshi YOSHIKAWA

Thank you for the query.

Would you be able to share the schematics snippet or waveform capture that could help in review?

Regards,

Sreenivasa

Hi 

If you are seeing 3V on your current design due to the silicon errata, there is no need for schematic review. 

Exposing 1.8V IOs to 3V will damage the part over time. 

Please see several older posts on this topic

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/863811/tms320c6748-advisory-2-3-18-s-work-around-a?tisearch=e2e-sitesearch&keymatch=advisory%25202.3.18#

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/651075/tms320c6748-tms320c6748-errata-sprz303h-2-3-18-dvdd18-can-pull-up-to-2-7v-when-using-dual-voltage-ios-at-3-3v

Hello Hiroshi YOSHIKAWA

Please refer to notes regarding the workaround on priority to minimize failures: 

based on past experience with customers encountering this issue where w/o the workaround the 1.8V gets lifted to 2.7V instead, we have seen devices failing to function within 2-3 days and there is damage where these units will not function.

It is important that you chose one of the recommended workarounds.

There are no additional details beyond what we publish in the errata.

Regards,

Sreenivasa

I have two ideas. The first is to add a shunt circuit. The second option is not to supply P1.8.
5.3 Recommended Operating Conditions of the data sheet JAJSDV5G states that "DVDD18 must be powered even if all of the DVDD3318_x supplies are operated at 3.3V." In implementing the latter, I would like to ask what kind of inconvenience will occur if DVDD18 is not supplied.

Hello Hiroshi YOSHIKAWA

Thank you for the note.

I am not sure if some part of the message is lost or missed.

Would you mind resending the message you wanted to send.

Thanks,

Sreenivasa

I added line breaks to make it easier to read.
------------------------
I have two ideas. 
The first is to add a shunt circuit. 
The second option is not to supply DVDD18.

The datasheet JAJSDV5G "5.3 Recommended Operating Conditions" states that
"DVDD18 must be powered even if all of the DVDD3318_x supplies are operated at 3.3V."
In implementing the second option, I would like to ask what kind of inconvenience will occur if DVDD18 is not supplied.
Why TI recommends that DVDD18 must be powered?

DVDD18 is not used other than C6748 on our board.
All of the DVDD3318_x supplies are operated at 3.3V

Best regards,
Hiroshi.

Hello Hiroshi YOSHIKAWA

Thank you for the note.

Please read through the links that Mukul has provided above. They have additional links inside and provides insight on the recommended solution.

Regards,

Sreenivasa

Hi Kallikuppa Sreenivasa,
I checked the all link in Mukul Bhatnagar's post,

but could not find any discussion about turning off DVDD18.

Hello Hiroshi YOSHIKAWA

The 2nd option is below. Where do you see the recommendation about turning off DVDD18.

Based on the above threads adding the cap seems to be the solution preferred. 

Choose a regulator for the DVDD18 supply (or grouped 1.8V supplies) that is
capable of actively regulating voltage up and down. Many high-efficiency switching
regulators switch current into the load only when the voltage needs to be raised and
rely on the load to pulldown the current. In this error condition, a regulator of this
type will not be able to compensate for the leakage current described above.
Synchronous buck regulators use external inductance to pulldown the regulated
voltage when necessary.

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/429351/about-dvdd3318_x-ramp-time-for-3-3v-in-table-12-of-errata-sprz303h-tms320c6748

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/747232/tms320c6748-tms320c6748-errata-advisory-2-3-18-dvdd18-can-pull-up-to-2-7v-when-using-dual-voltage-ios-at-3-3v

Regards,

Sreenivasa

Hi Kallikuppa Sreenivasa,

The 2nd option is the solution I thought of.
I am aware that it is not recommended.
I just want to know why we have to supply DVDD18.

"DVDD18 must be powered even if all of the DVDD3318_x supplies are operated at 3.3V."

Best Regards,
Hiroshi. 

Hello Hiroshi YOSHIKAWA

Thank you for the note and understand your question.

Let me check internally if i can find an answer and update you. 

Please expect a delay in response.

Regards,

Sreenivasa

Hello Hiroshi YOSHIKAWA

I checked internally and do not have an answer to share.

Since the information seems to be internal device related and the datasheet has the recommendations,  i am not sue if i can find the answer and share.

Regards,

Sreenivasa