MSP430F2274-EP: Properly configuring I2C port during low power mode

adevries

Hello,

I am creating a circuit designed to be partially powered down for long periods of time. When it is fully powered, my microcontroller will act as an I2C slave and respond to commands on the bus. However, when the circuit is partially powered down, the microcontroller will continue to be powered off of a battery, but the I2C bus and master will not be powered. In this case, what is the best way to configure the I2C port to minimize power loss? Is it safe to set the pins as GPIO outputs and set them low? Will that cause any problems when the circuit powers back up and needs to use the I2C bus again? Or is it better to set them as inputs and pull them up off of the battery rail? If so, what's the highest resistance I could use? I have provided an image to better explain this.

When fully powered on, VCC = VBAT = 3.3V. When partially powered down, VCC = 0V and VBAT = 3.1-2.5V.

over 7 years ago

0 Kirby Kruckmeyer96848 over 7 years ago

TI__Genius 17125 points

Hello,

The person who can answer this the best is out of the office right now but will answer your question on Monday, April 15 when he gets back in the office.

0 adevries over 7 years ago in reply to Kirby Kruckmeyer96848

Intellectual 955 points

Great! Thank you for the update

0 Wade Vonbergen over 7 years ago in reply to adevries

TI__Guru 62930 points

Adevries,
I believe your best approach to minimize leakage would be to place the pins in input mode. Assuming VCC=0, these inputs will be pulled to ground and not partially turn on the input stages.
If you need to detect re-configuration of the the I2C when VCC comes back up, you could use these inputs to trigger interrupt to reconfigure back to I2C mode.

If this answers your question, please click "Verify it as the answer"
Regards,
Wade

0 adevries over 7 years ago in reply to Wade Vonbergen

Intellectual 955 points

Hi Wade,

Thanks for the response. That makes sense. So, in general, to minimize power consumption with the MSP430, it's important to make sure all pins are at VCC or VDD, right? So if the pin is unconnected, the easiest way to accomplish this is by setting it as an output and as high or low. If the pin is externally connected to something that would pull it to VCC or VDD, then the same thing is accomplished. Am I understanding that correctly?

Thanks

0 Wade Vonbergen over 7 years ago in reply to adevries

TI__Guru 62930 points

Correct. Most important is to not allow floating inputs. An unloaded output would also be appropriate.
Regards,
Wade

0 adevries over 7 years ago in reply to Wade Vonbergen

Intellectual 955 points

Great, thank you very much for the help Wade!

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MSP430F2274-EP: Properly configuring I2C port during low power mode