bno55 at 1.8v logic

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psavoy
 
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bno55 at 1.8v logic

Post by psavoy »

I have the adafruit sensor bno55 and see from the https://learn.adafruit.com/assets/24667 - that I only need 4 interfaces from the micro controller I intend to use. The logic at which the i2c master (my micro-controller) is working is 1.8v.
Can I only supply the 1.8v at the Vin and still get the bno55 working? Doesn't the bno55 data sheet say that supply voltages for uC/IO and sensor domains are separate and would still need at 3+ ? In my case 3.3v?
How would I go about giving this supply ?


Thanks,
Pavan

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adafruit_support_mike
 
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Re: bno55 at 1.8v logic

Post by adafruit_support_mike »

It won't work.. the minimum voltage the BNO055 can use is 2.4v.

Getting that voltage will depend on how the rest of the system is powered. None of the standard battery chemistries operate at 1.8v, so the 1.8v system will probably take its power from at least a 3v source, and possibly a LiPo of 5v DC connection. If so, those would be the easiest places to get power for the BNO055.

You'll probably need a level shifter for the I2C signals, and we don't have anything designed to work within 1.8v thresholds. The constraints on 1.8v are tight enough that I'm not sure what kind of circuit you'd need.

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psavoy
 
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Re: bno55 at 1.8v logic

Post by psavoy »

You're right about our setup, it is 5v when over USB, 3.3v output from battery, there's an SMPS that gets it to 1.8v for all the digital logic.
The 3.3v min is with the Adafruit version of BNO55 or the chip in general.
The chip's electrical specs kind of suggests VDD can be say 3.3v and VDDIO for UART and I2C can be 1.8v (>min of 1.7v), So technically can I2C work at 1.8v?

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Re: bno55 at 1.8v logic

Post by adafruit_support_mike »

The BNO055 can probably do it, but the breakout has a level-shifting circuit that connects pull-ups on the I2C pins to the onboard 3.3v regulator. You'll need to work around those, and I don't know if the level-shifting mosfets on the breakout will work when connected to 1.8v.

The board just wasn't designed to operate at that level.

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