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BQ25895: Quiescent battery current

David Drori
Prodigy 90 points

Part Number: BQ25895

I am designing a product that includes the BQ25895 and I wish to estimate the total battery discharge current due to the BQ25895 itself when all of the following idle system conditions are valid:

  1. The USB charger is not connected to VBUS;
  2. Voltage boosting is disabled; and
  3. The external load on the SYS pin is a small idle load of around 1 mA.

My hope is that the BQ25895 itself will draw no more than 1 mA or thereabouts, so that the total battery discharge current will not exceed a few milliamperes.

Referring to the datasheet, under the Quiescent Currents heading, IBAT  - battery current (BAT, SW, SYS) in buck mode - is quoted as 32 microamps (typical) for "High-Z mode, no VBUS, BATFET enabled, (REG09[5]=0), battery monitor disabled, T<85°C". This is well within the aforementioned maximum quiescent battery current draw target of around 1mA. However, the references to High-Z mode and battery monitor being disabled concern me.  How do these affect the quiescent battery current and how should I take them into account while estimating the quiescent battery current draw under the idle system conditions I have listed above.

What concerns me most of all are the IBAT(LOAD) and ISYS(LOAD) parameters, listed under the Battery Charger heading, whose minimum values are quoted as 15 mA and 30 mA, respectively. What do these values represent, and could either or both of these be applicable to estimating the total battery discharge current under the idle system conditions listed?

  • 0
    TI__Guru**** 177056 points
    Hi David,

    The charger goes into HiZ mode whenever VBUS is removed and OTG is disabled. The battery monitor is the integrated ADC. During an ADC measurement, the quiescent current jumps over 10X. As long as you don't turn on the ADC for continuous reading, IBAT(HIZ)= 32ua typical.

    the IBAT(LOAD) and ISYS(LOAD) are features not generally used. The intent was to allow a customer to write host software that would try to detect if a battery was present by pulling a fixed amount of current from BAT or SYS and then monitoring the amount of voltage drop on BAT/SYS. REG03 bit 7 controls IBAT(LOAD). It is normally disabled.
  • 0 in reply to Jeff F
    Prodigy 90 points
    Hi Jeff,
    Thank you for the quick and full response, which dispels my concerns about the quiescent current.