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How to sense battery voltage when connected to a BQ24253?

Other Parts Discussed in Thread: BQ24253

Hi,

We are using a bq24253 to power our system as well as charge the backup battery. Now, I want the MCU's (MSP430F67xx) ADC (ADC10 in this case) to be able to read the battery's voltage and record the battery charge (the correlation between voltage and charge/discharge status will be done separately by us).

Now, since the battery is charged in a switched manner, the output voltage keeps varying!

Any suggestions would be highly welcome.

  • There may be a slight ripple voltage on the battery but it should be small.  Where are you measuring the voltage?  Do you have a load on SYS that is causing the battery to enter supplement mode?  If so, this will cause a large ripple on the battery.

    You could temporarily disable charge to take a measurement.  Or, you could place an RC filter off of the BAT pin and take the measurement at that point.

  • Hi Jeff,

    I have a direct connection from the BAT+ pin from the battery to the ADC input of my MCU (MSP430). I hadn't yet explored the option of disabling charge to take measurement. I think that would be the most accurate manner of measuring the battery voltage. But, the RC filter option also sounds promising. Wouldn't the RC filter prove to be a problem for the BQ24253's battery detection mechanism or charging mechanism?

    The SYS load hasn't yet proved to be a problem large enough for the battery to enter supplement mode, but we are still working on the design and increasing the peripherals for it to power, so we aren't 100% sure yet.
  • If the RC is sized properly (i.e. with large time constant) then it will not affect the battery detection routine but your measurement will be a bit historical.

  • Thanks Jeff, this sounds like a good idea. I will implement this in my design after a little testing.