BNO055: should pins 15 and 16 be connected?

[SteveF]

We have just designed a board with BNO055 on it. As per the datasheet (Rev 1.7, Nov 2020), we left pins 15,16 "DNC" - unconnected.

On powering up the board, the BNO055 does not respond to I2C commands (no ACK to slave address).

We had previously prototyped the system using 3rd party BNO055 eval boards, and it worked fine.

The only difference we can spot is that pins 15 and 16 are connected to GNDIO on every eval board we can find.

We see the datsheet also used to have these pins connected to GNDIO, but it got updated in Rev 1.6, Feb 2020. There was a firmware update also just before this.

The ICs on our board may be several years old, so might it be possible that the older firmware in these does actually need pins 15 and 16 connected to GNDIO?

[BSTRobin]

Hello SteveF,

This is official schematic of BNO055 shuttle board. You could pin 15, pin 16 were not be connected, the same with data sheet description.
https://www.bosch-sensortec.com/media/boschsensortec/downloads/shuttle_board_flyer/bst-dhw-fl039.pdf

For "On powering up the board, the BNO055 does not respond to I2C commands (no ACK to slave address)."
Two suggestion:
1.Could you give out your schematic to check?
2.You could read chip ID in your promgrame first, and capture I2C waveform to check actual communication.

[SteveF]

Thanks BSTRobin.

The shuttle board schematic only shows pins 15,16 wired to the connector, so their use is not explained.

Here is the relevant part of our schematic and a scope grab of the I2C trying to talk to the device (noisy because our software engineers don't fully understand how ground clips should work!).

We have a few other I2C devic es on the board, and they all work fine.

[BSTRobin]

Hello SteveF,

After review your schematic, pin 15, 16 not connected to the ground as per the reference design. These two pins should follow reference design connection.

[SteveF]

So, the latest datasheet is wrong then?

That's not very helpful.