BNO055 power on reset issues

[brentbop]

I'm trying to resolve a persistent issue I'm having with a BNO055 IMU on a custom PCBA. I'm communicating via I2C and am experiencing different behavior between device reset (using "Power on Reset" reset pin) with and without power cycling. In situations where I reprogram my MCU and start directly into my application code without power cycling, the IMU will respond with NAKs to any and all read/write messages. If I power-cycle the system, it works correctly. In both scenarios I'm pulling the reset pin low for ~25ms, pulling the reset pin high, and then waiting for ~725ms before initiating I2C communication. All other signals (COM1, COM2, PS0, PS1, nBOOT_LOAD_PIN) are connected to VDD or GND directly or through a 10kΩ resistor. A partial schematic is attached.

The firmware is heavily based upon the BNO055 XPlained Pro example code and is being run on a SAMD21G18A.

Can you help me to understand the differences in behavior between device reset for the BNO055 from an 'unknown' state and from a power-on state? Do I need to set the SDA/SCL lines to a certain level before/during/after Power on Reset?

Attached are logic analyzer screenshots of the system failing without power cycle (BNO055_noPowerCycle.png) and working with power cycle (BNO055_withPowerCycle.png), as well as a partial schematic (BNO055_sch.png).

[jbthompson]

Hi, you mentioned that Pin10 is a digital output that indicates when the part is executing bootloader code and should not be connected to ground?

The datasheet of the BN0555 says it should be connected to GND... Is there a mistake in the BNO055 Datasheet?

See snapshot:

[o_o]

That datasheet mistake has been corrected many years ago... unfortunately some old datasheet versions are still circulating on the internet.

Always refer to the latest version of the datasheet here : https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BNO055-DS000.pdf

[jbthompson]

Hi, we've updated our design based on your feedback and wanted to know if our new BNO055 design is valid.

We've added some circuitry to be able to change between I2C or UART mode using a GPIO from our MCU (notes in schematic).

We've added more capacitance as you suggested and added an external crystal to mitigate the power on reset issue.

Any feedback on our new design would be greatly appreciated.

[o_o]

Looks good to me. But if your MCU supports i2c, I really cannot recommend using UART interface, unless you must connect it to a host that does not support i2c.

[jbthompson]

Thank you.

In regards to the UART we just want to have the ability to switch for testing purposes or to interface with another host that uses UART (as you mentioned).