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BQ24195L: How can solve the Vsys ripple become too large when BQ24195L power on without battery?

Harrison Wang
Intellectual 280 points
Part Number: BQ24195L
Other Parts Discussed in Thread: BQ24195

Because our design requires that the system should be able to start up normally even without battery. However, when the system is started up without battery, the output ripple of Vsys is very large, which directly leads to the abnormal output of PMIC voltage at the back end. The system cannot get up and the registers cannot be configured through I2C.

So we need a solution that allows the BQ24195L Vsys waveform to work properly (or not in PFM mode) without the battery and the register configuration.

The Vsys waveform when BQ24195L power on without battery is below:

The Vsys waveform when BQ24195L power on with battery is below:

  • 0
    TI__Guru 57721 points
    Hi,

    When no battery is attached and charge is enabled by default, the charger sees the capacitor on BAT as a really small battery and goes through the normal stages of charging, termination, discharge then repeat. You can prevent this by disabling charge when the battery is removed.

    If I2C communication is not available to toggle the Charge Enable bit of the charger:

    1. It is ok to utilize the TS pin of the charger with the NTC thermistor that typically comes with battery packs. Essentially, when the battery is removed, it would trigger a TS fault on the charger that would disable charging.

    2. It is also ok to add a load switch or MOSFET to isolate the BAT pin of the charger and the battery cell voltage, and add some simple logic circuit to control the /CE pin.

    Thanks,

    Ning.
    Please click "This Resolved my issue" button if this post answer your question.
  • 0 in reply to Ning T
    Prodigy 20 points

    Hi Ning,

    1. I force to pull the charge enable pin, /CE high to Vregn to disable the charger of BQ24195L.  When I plug in DC power to BQ24195L, the output of STAT pin is high which means the charger is disabled and the Vsys  output a 3.7V  for 200ms at first and then the ripple became huge which is absolutly abnormal.  what's the reason why this abnormal action happens?

    2. Whenever I attached the battery to the BAT pin before power on or after power on, the charger BQ24195L outputs properly.

    3. Can BQ24195L work properly without battery attached? It seems that BQ24195L enters into low light mode without battery attached.

    4. I just want to know does BQ24195L charge the battery even if  /CE pin is pulled up in hardware in case I2C communication is not available.

  • 0 in reply to guomin zhang
    TI__Guru 57721 points
    Hi,

    1.In order to improve light-load efficiency, the device switches to PFM control at light load when battery is below minimum system voltage setting or charging is disabled. Please refer to Fig 39 on the d/s.
    2. The device may operate normally without or with battery.
    3. Battery charging is enabled when REG01[5:4] = 01 and CE pin = Low. CE pin must be pulled high or low.
    4. It is highly recommended to get familiar with the charger operation by testing the BQ24195/L EVM (www.ti.com/.../bq2419xevm).

    Thanks,

    Ning.