• State TI Thinks Resolved
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 35 views
  • Users 0 members are here
Support feedback
Options
Options
Related

BQ25731: Fuel gauge control

Szymon Sidorkiewicz
Prodigy 10 points
Part Number: BQ25731
Other Parts Discussed in Thread: BQ25730, BQ40Z50

Tool/software:

Hi!

I'm a student beginning in the world PCB design.

During my internship I need to design a 1s7p battery charger. My choice landed on the BQ25730/31. To design my board I follow the BQ2573X evaluation module aswell as the typical application of BQ25731.

I wish to make a fuel gauge for the project. The first idea was to simply estimate remaining energy based on battery voltage but I would be affected by the load and age of batteries.

I noticed that I can monitor the system power usage from PSYS pin configurable via I²C. As far as I understood, the pin outputs current proportional to the power consumption. Tied with a resistor it allows to create a voltage drop on the resistance clamped at 3.3V.

Unfortunetaly, neither of the documents attached above specify how to use the PSYS pin. The first idea is to periodically monitor PSYS voltage by the ESP32, however I'm not sure this solution will be quet precise to estimate remaining energy. The other idea (not elaborated yet) would be to use an integrator that resets every time I read the analog value of the integrator. 

Are there other, maybe simpler solutions that you would recommend?

Thank you

Simon

  • 0
    TI__Mastermind 33205 points

    Hi, Simon,

    Did you know PSYS has an internal ADC? You can use I2C and check the ADC_PSYS to monitor the system power. You can also use your own ADC.

    The fuel gauge needs to do coulomb counting. Why not use a fuel gauge IC, such as BQ40Z50?

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    Prodigy 10 points

    Hi Tiger,

    I completely misset the existence of this register!

    As far as I understood, the voltage of PSYS pin still needs to be configured via external resistor? For instance, the whole system can consume up to 30W. With 1µA/W gain I can hook up 100k ohm resistor between PSYS and GND to read 0-3V voltage on the dedicated register. 

    I was thinking to write a dedicated firmware to control the power consumption by reading PSYS voltage at constant time step to estimate energy consumed (unfortunately, with the error of unknown consuption between readings).

    I wonder why fuel gauge needs to count coulombs? Aren't Wh measures more acurate, especially with voltage fluctuation of the battery? 

    To protect the battery I use the BQ29700 but BQ40Z50 is absolutely worth checking with all the functions provided, thank you for the part number but at this stage it's too late to add it to the project :(

    Best regards,

    Simon

  • 0 in reply to Szymon Sidorkiewicz
    TI__Mastermind 33205 points

    Hi, Simon,

    Coulomb counting is the same concept of integral of PSYS over time. You count joule instead. 

    Good luck with your project. 

    Regards,

    Tiger