BQ25121A: Correctly identify transition from VIN to BATT

agusta mir

Part Number: BQ25121A

Hi,

I am trying to find a good way to detect the transition from VIN to BATT on the BQ25121A part. I read all registers at an interval of 3s. When on battery power, I drive CD high to enable I2C and read the registers. When VIN is detected, the I2C interface is enabled and CD needs to be pulled down to enable charging. I pull CD low as long as VIN is available to enable charging. Now to my main question: Upon VIN removal, last known status of the CD is "low" with power available. In the next read, when the device is actually on battery power, my read fails as I assumed VIN was still available. Can you suggest an method to handle this transition?

over 5 years ago

0 Raheem over 5 years ago

TI__Mastermind 21590 points

Hello,

You can use the /PG pin to determine what state /CD should be

0 agusta mir over 5 years ago in reply to Raheem

Intellectual 480 points

Thank you. Unfortunately, I don't have the ability to check PG due to lack of host pins.

0 Raheem over 5 years ago in reply to agusta mir

TI__Mastermind 21590 points

Are you able to toggle the /CD pin when you get a NACK on I2C?

0 agusta mir over 5 years ago in reply to Raheem

Intellectual 480 points

Yes, I can. There is no issue per-se in retrying with the CD pulled low. At that point, I may have to decide how many times to retry before declaring a real "fault" ie device not responding.

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BQ25121A: Correctly identify transition from VIN to BATT