TXS0108E: Issue interfacing this part to SD Card (level translating b/w 1.8V and 3.3V)

Mohan Sattineni

Part Number: TXS0108E

Hi,

I am using TXS0108E as level shifter between host FPGA and SD Card. I observed an issue in the response from SD card for CMD8 during SD card initialization. When I probed the CMD line on both the sides of level shifter I see that the host side CMD line is not tracking SD card side CMD line at some point.

I have checked with Xilinx and Trenz and they do recommend using SD-card specific level translator. However I didnt understand the reason behind it and why it is failing with TXS0108E.

Any reason on why this is failing and any further debug suggestions are really appreciated.

Mohan.

over 5 years ago

0 Karan Kotadia over 5 years ago

TI__Genius 16735 points

Hi Mohan,

The TXS has internal One-Shots that get triggered to help have a faster transition rate. If it is falsely triggered, what you are seeing may happen. False triggering can occur if the input is too noisy, output is not properly matched or long traces are being used. Can you provide me with a schematic? Are there any external pullups on the lines?

Thanks!

-Karan

0 Mohan Sattineni over 5 years ago in reply to Karan Kotadia

Prodigy 30 points

Hi Karan,

There are no external pullups.

Below is the schematic.

I also dont see any major noise on the input side (in the plot attached in earlier post).

The other side is connected to FPGA directly.

Mohan.

0 siva kumar5 over 5 years ago in reply to Mohan Sattineni

Prodigy 100 points

Hi Karan,

Even PCB trace length also very short as ~20.19mm (795.17941mils), pls refer below snap shot for details.

Where, U12 - TXS0108E (leel translator) and CON!) - SD card connector.

Regards,

Shiva

0 Mohan Sattineni over 5 years ago in reply to siva kumar5

Prodigy 30 points

Hi Karan,

We are waiting on your reply to check if we have to go with a different level shifter. Can you please help us with more debug and suggest if we have to use SD card specific level shifter?

Mohan

0 Karan Kotadia over 5 years ago in reply to Mohan Sattineni

TI__Genius 16735 points

Hi Mohan,

You don't need to switch to a SD card specific level shifter. Can you zoom in to the edge of the input that is being glitched?

I think the input might have noise or if the input edge is slow, this might be causing a false trigger to the device.

Thanks!

-Karan

Logic

Logic forum

TXS0108E: Issue interfacing this part to SD Card (level translating b/w 1.8V and 3.3V)