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BQ24192: Charging current will not go over 1.05 A

Part Number: BQ24192
Other Parts Discussed in Thread: BQSTUDIO

Hi,

we use in our project the bq24192 as a charger for 1Cell-LiIon  Battery.

I set externally at ILIM Pin a resistor (R=180 Ohm) to set the charging current to approx. 3A.

When i connect an ext. power adapter with 5V a charging current of approx. 1.1A is used. I tried to change the charging current in the edit field ICHGto a value higher than 1.1A but without success. Any value under 1.1A will be accepted but higher not.

Can someone tell me what I'm doing wrong?

Here are my settings :

Regards,

Alex

  • Hi Alex,

    Just to confirm the behavior you are seeing, attempting to write a bit value to the ICHG field greater than 1.1A (ICHG = 0b001010) fails. Does this mean that reading back the register value reads the previous value or that the actual charge current does not change even though the register value has changed?

    Best Regards,

    Juan Ospina

  • Hi Juan,

    at my first post i was using a battery simulator (Keithley 2281S) and the model used has not covered exactly my real physical battery. Therefore I was not able to see a higher current.

    Now I use a real battery, but I'm facing similar problems. Now the max. delivered current by the charger is around 1.7A even i've set 2.048A. And yes the charge current will not change if i change the value in the register.

    Another issue is that  VSYS never go in regulation although the adapter port is not available and the VBAT is lower than Minimum System Voltage set at 3.5V.

    Discharging the Battery:

    Charging the Battery:

    Any idea for this behaviour?

    Regards,

    Alex

  • Hi Alex,

    Thanks for the additional context.

    With regards to the Discharge state:

    adapter port is not available

    Since the separation between battery and SYS is only the Q4 battery FET, there isn't really a way to regulate the SYS pin voltage without an adapter present. So SYS voltage without an adapter will be at most BAT voltage minus the voltage drop across the Q4 FET. If you need a higher voltage you can use the OTG boost mode to get 5V which will be present on PMID or VBUS.

    With regards to the Charging state:

    Although there is no load at SYS, it appears to only be at 4.08V. This seems to indicate to me that the input current is being limited. I would double check your input current limit settings, your input voltage limit, the voltage at the VBUS pin while charging, and any compliance current limit that might be set for your input. 

    Best Regards,

    Juan Ospina

  • Hi Juan,

    I had the same thoughts as you till i read the datashhet more accurate regarding the "Minimum System Voltage". In the pin description I read this

    and I was confuse . But you where right. The SYS Voltage will be regulated only when the VBUS is present AND Charging is disabled AND Battery Voltage is less than the "Minimum System Voltage". Otherwise pin SYS it will have the charging voltage. I checked this and i can confirm this.

    Concerning the charging current limit I've done your proposal but without success. But in the meantime I solved another issue. I had also the problem that after aprox. 20-25 seconds of changing the charge current below 1.7A (for example the new value was 1024 mA) the value has changed back to the default one, in case of bq24192, 2048 mA. 

    The cause was the absence of the "Periodic resets". It was set to "OFF". In the case that the I2C Watchdog Timer Limit will be "disabled" instead also works fine.

    But now I'm wondering how to do this settings when i use bq24192 together with bq27531 and bqStudio? 

    By accessing for example the REG05 i can't set the Bits 4 and 5 to disable the I2C Watchdog Timer because these bits are RESERVED (see picture below). 

     

    Any idea how to deal with this?

    I wish you a nice weekend.

    Alex

  • Hi Alex,

    Concerning the charging current limit I've done your proposal but without success.

    Can you share the register values while the 1.7 A charging is taking place? If possible can you also share the VIN voltage or a waveform during this state.

    Unfortunately, I'm not as familiar with the BQ27531 so I recommend creating a new thread for that particular issue. It's possible that the BQ27531 handles the watchdog kicking on its own.

    Best Regards,

    Juan Ospina