topic Re: K22 I2C0 pull downs crash I2C bus in Kinetis Microcontrollers

K22 I2C0 pull downs crash I2C bus

kevinlfw — Thu, 05 Jan 2017 20:35:57 GMT

I'm working with the K22 and removed power from the chip, however kept I2C0_SDA and I2C0_CLK on PORTB connected to the I2C bus. When I keep them connected while the chip is powered down, it pulls the entire I2C bus down. When I remove the K22 from the bus, the bus operates as it should.

What can I do, from the K22 side, to prevent this from happening, as I believe the pull-down is internal to the chip itself?

Re: K22 I2C0 pull downs crash I2C bus

mjbcswitzerland — Thu, 05 Jan 2017 21:04:55 GMT

Kevin

I think that a non-powered K22 will look like a diode to GND to the I2C bus (due to its passive GPIO protection circuitry). Probably you need to put MOSFET switches on the two lines and only switch them on when the K22 is powered.

Regards

Mark

Re: K22 I2C0 pull downs crash I2C bus

egoodii — Fri, 06 Jan 2017 01:31:28 GMT

Exactly that cause -- I would go with a 'fully pre-designed' isolation concept like PCA9617A, or such from that family.