BMI160 pins 2 and 3 - safe to connect to ground?

IDEngineer · ‎2019-01-29

The BMI160 spec sheet says pins 2 and 3 are high impedance when the secondary I2C interface is not being used. The spec sheet also *implies* that the secondary I2C interface defaults to disabled upon a power cycle. The question is, can pins 2 and 3 be safely and permanently connected to Ground if the secondary I2C interface will not be used?

The reason this matters is because the BMI160 is pin and package compatible with the ST LSM6DS3, which means they can serve as each other's second source. (The registers are entirely different so firmware must determine the installed device, but that's trivial.) The only question is pins 2 and 3, which the LSM6DS3 wants connected to either VddIO or Ground.

Obviously, if the BMI160 has pins 2 and 3 at high impedance, then having them connected to Ground won't matter. The concern is if we can rely on pins 2 and 3 reliably at high impedance after a power cycle. We could get an overcurrent condition on those two pins if they were to power up trying to act as outputs which are shorted to Ground.

Anyone have experience with this question? Anyone use the LSM6D3S and the BMI160 as each other's second source?

Thanks!

IDEngineer · ‎2019-01-30

I opened a ticket with Bosch-Sensortec on this question and got a response in less than 24 hours:

>>When BMI160 powered up, the secondary interface will be put in high Z mode by default. So you can connect it to GND or VDDIO to compatible with ST sensor. Just one thing you need to watch out, there should be no change for secondary interface in your code, otherwise it will be big risk.<<

So the answer is: Yes, the BMI160 and LSM6D3S can act as a second sources for each other, as long as you don't intend to use the BMI160's secondary I2C interface. Please note the "typical" power supply rails are different, but their acceptable ranges overlap so you can either standardize on a common supply (2V5 would work for both) or selectively populate the board with appropriate component values based on which part is installed.

Hope this helps others who are considering the LSM6D3S for new designs!