NUCLEO-L552ZE-Q SDMMC: CK and D3 shorted

[Fredlaks]

Hello,

on two separate species of the NUCLEO-L552ZE-Q board i observe for the SDMMC interface that  CK and D3 is shorted. I observe the CK signal appearing on D3 as well as CK when probing using an oscilloscop.

Further investigation show that there is an electrical short on the board itself, verified with a multimeter. This is with the µSD adapter disconnected, so the NUCLEO board is the only possible source of this short.

Doing the same verification on a second NUCLEO-L552ZE-Q board, i see exactly the same short between D3 and CK.

As a result i can only communicate with a µSD card in 1-bit mode with SDMMC, and only when D3 is not connected to the µSD adapter. 

I haven't been able to find this short between SDMMC CK and D3 in the documentation, so i wonder if this is intentional short, or not?

Or is there a solder bridge/0 ohm resistor/jumper to disable this short?

[Peter BENSCH]

I had a look at the GERBER data of the NUCLEO-L552ZE-Q and found:

• a track from PC11 (pin 112) on the top layer to CN8.8
• a track from CN8.8 on the bottom layer to CN11.2

No other component, jumper or any other connection is visible there.

Are you 100% sure that you are measuring the short circuit between CK (CN8.10 or CN11.3) and D3 (CN8.8 or CN11.2)?

Regards
/Peter

[Peter BENSCH]

I quickly inserted the net, i.e. the tracks on PC11, as a screenshot:

• top layer green, opacity 38%
• bottom layer red, opacity 100%
• with the tracks highlighted slightly more brightly.

It is easy to see here that only CN8.8 and CN11.2 are actually on the track. The other layers have only cut-outs there and no connection at all: