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Original question:

BQ25606: Battery not present and current limit

BQ25616: Battery not present and current limit

Ferdi Tjandra
Prodigy 20 points
Part Number: BQ25616

Hi,

I have the same exact issue as in this thread here:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/963322/bq25606-battery-not-present-and-current-limit

I have a 12V boost controller (MCP1665) connected to the output of the BQ25616 (SYS). I want to draw ~500mA from the 12V boost controller.

VBUS is 5.5V. D+,D1 are floating. I also tried to short D+ and D- to make the input current limit 2.4A.

With the battery connected (3.7V Li-Ion), I can draw the 500mA, but the battery is discharging even though I have 5.5V coming into VBUS.

I tried connecting VBUS directly to an external power supply just to make sure that it wasn't current limiting externally. I went all the way up to 13V and the battery was still discharging.

With no battery connected, the entire BQ25616 works fine until I try to draw any significant current (150mA on the 12V boost controller) - it then shuts down causing my entire board to reset.

The BQ25616 is completely powered up before I try to draw the current, so it's not the issue of the 200mA limit on startup.

Is the BQ25616 not designed to supply SYS directly from VBUS with no battery? It seems there are a lot of posts with this same issue with no solutions.

Here is my schematic:


Thanks.

  • 0 in reply to Ning T
    Prodigy 20 points

    Hi Ning,

    No, that is not it.

    Like I mentioned, the BQ25616 is completely powered up (for minutes), before I enable the load that's connected to the 12v boost controller.

    Also, that would not explain why the battery is discharging even though there is power on VBUS.

    It seems like no matter what, the input current is being limited. Now that I think about it, that also includes the charging current. I've never seen it charge at more than ~200mA even though it's set to 1.5A.

    Thanks.

  • 0 in reply to Ferdi Tjandra
    TI__Mastermind 21895 points

    Hi Ferdi, 

    Beyond the information Ning shared about Vsys not starting up normally when there is a load on SYS in no battery condition, the device should not have any issue supplying 500 mA to sys when no battery is present. I have verified on BQ25616 EVM with your test setup that device does not have issue supplying current up to Input limit to sys. When D+/D- are floating current limit will be set by ILIM pin.

    In regards to your issue of battery discharging have you attempted to charge the battery without sys load attached? When the battery is discharging is the stat pin blinking to indicate a fault? If device is in a fault state the battery will not charge and instead power sys_load.

    I verified on EVM using same resistor settings as your schematic that BQ25616 is able to charge battery at 1.5A and provide upwards of 500 mA to SYS. 

    Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 20 points

    Hi Garrett,

    Thanks for confirming on the EVM that it should be working like I expect.

    Now to figure out why it's not working on our board.

    The battery charges fine with no load attached (stat led is solid). But again, for some reason I have never seen it charge at anywhere close to what ICHG is set to (~1.5A). I just tried charging a completely discharged battery and it's only charging at 680mA (measured going into the battery).

    If I turn ON the load, stat led remains solid ON while the battery is discharging. The only time I have seen stat blinking is if I remove the battery.

    I checked our BOM against the schematic and everything matches, but is there a component that you suspect could cause this kind of behavior? I tried shorting D+ and D- to take ILIM out of the equation, but that made no difference.

    Thanks.

  • 0 in reply to Ferdi Tjandra
    TI__Mastermind 21895 points

    Hi Ferdi, 

    To first focus on the issue of the battery not charging at your ICHG setting are you able to provide waveforms of Vbus, Ibus, Vbat, and Ibat when your system load is disattached? Referring to tables 9-1 and 9-2 on page 19 of the datasheet the input current limit via D+/D- detection will never be lower than 1 A. If you are unable to observe a charging current of 1 A then you might want to double check your resistor connection to ILIM pin and confirm your input adapter has adequate power.  

    Ferdi Tjandra said:
    The only time I have seen stat blinking is if I remove the battery.

    LED blinking is expected when battery is removed. This does not necessarily mean there is a fault. The LED blinks because the device switches back and forth between charging and charge complete when no battery is attached.  

    Can you also provide measurement of Vbus, Ibus, Vsys, Isys, Vbat, and Ibat when you have both load and battery connected? This will help to debug why the battery is discharging with Vbus connected. 

    Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 20 points

    I think an easier first test case would be to remove the battery from the equation and figure out why I am unable to power the load through only VBUS.

    But I just went ahead and ordered the BQ25616EVM as I think it would make troubleshooting easier on my end.

    Thanks.

  • 0 in reply to Ferdi Tjandra
    TI__Mastermind 21895 points

    Hi Ferdi, 

    Okay I agree removing either the battery or the sys load from the equation will be best for initial debugging. If you want to focus on the no battery case that will work.

    When you have the evm please look to capture Vbus, Ibus, Vsys, and Isys so we can debug why you are currently unable to draw larger amounts of current to System load. 

    Regards,

    Garrett