I2C voltage level dropping on SBRIO

[DavidT]

Hi All,

I've been successfully using an Sbrio-9627 with a 9694 mezzanine card to read an I2C sensor (MPU-9250) via FPGA->RT for a few weeks now without issue.

Not knowing why, the signals now showing up on my RT Host vi are not continuous with byte signals going very intermittently to full scale (255) on all bytes. I have checked to connections and it looks like the 3.3V supply is dropping to 2.5-2.6V when I connect the MPU sensor. I don't know if this is an issue but the MPU states a VDD operating range of 2.4V to 3.6V. I don't know if this has always been the same but I didn't have any issues.

I also tried a new MPU and same issue. I connected both MPUs to an Arduino and this did not have a problem reading continuous data.

Does anyone have any ideas on how maintain 3.3V and if there's anything else I could try?

Regards,

Dave

[crossrulz]

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@DavidT wrote:

Does anyone have any ideas on how maintain 3.3V and if there's anything else I could try?

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That sounds like you are drawing more current than the power supply can handle.  Use a power supply that can handle more current.

[DavidT]

Hi crossrulz,

The MPU has a current draw of 3.7mA and the sbrio is plugged into the AC socket? I've attached a screenshot of the MPU specs which does state nominal operating voltage of 2.5VDC but something we overlooked in the datasheet was the operating current. The 3.3V DIO lines have a max current limit of 3mA.

Is it possible we may have damaged the 3.3V and DIO lines?

Regards,
Dave

[crossrulz]

Are you saying you are powering the MPU with a digital line?  That is a big no-no.  Have a separate supply for the MPU.

[DavidT]

It's being powered by the FPGA_VIO pin from the 9694 Mezzanine board - this is stated as " I/O voltage for the FPGA 3.3V pins" in the manual.

I have tried running from a separate supply i.e. the arduino 3.3V supply but I did not get any signals but happy to try again.

[DavidT]

Update - I've tried powering it via 3.3V power from an Arduino UNO card but I don't receive and data.