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BQ24297 power up delay

Other Parts Discussed in Thread: BQ24297, BQ24297EVM-021

We are observing unexpected behavior of your BQ24297 battery charger.
When powering up from Vbus with a battery connected the system powers up in 198mS. This seems very long but would be usable.
When powering up from Vbus with no battery connected the system requires about 850mS to power-up
We have the charger pin strapped for 1.5A maximum input current , the OTG pin is pulled to Vbus, and the CE pin is pulled low.
Any idea why the no battery case takes so long and is there anything we can do to fix this.

  • Do you have any SYS load during power-up? It would be helpful if you may share the startup waveforms for VBUS, VSYS, ISYS and SW.

    Thanks!

  • SYS has a load of about 20mA, it runs off of a 3.3V regulator which is connected to SYS.

    When powering up from Vbus with a battery connected the system powers up in 198mS. This seems very long but would be usable. (see Power_up_with_battery.jpg)

    When powering up from Vbus with no battery connected the system requires about 850mS to power-up (see Vbus_current.jpg). There is a 250mA current spike at the point where RGEN turns ON and the SYS pin voltage begins to ramp. Vbus_to_PMID.jpg shows the PMID voltage pulsing during this period before finally turning fully turning ON. Vbus_to_RGEN.jpg shows the RGEN voltage delay.

    We have the charger pin strapped for 1.5A maximum input current , the OTG pin is pulled to Vbus, and the CE pin is pulled low.

    I have scope pictures in a ZIP but your system does not seem to accept it.

  • Hey Roger,

    Are you using the TI EVM for this analysis, or do you have it running off of a custom board?

    What is your battery voltage?

    Also, if you could directly attach the pictures of the waveforms, that would be helpful as well. You can just attach them (if you do not see any screen to do that, make sure you are in Rich Text Formatting mode) 

    Once you get the next screen, just attach the pictures individually instead of in a zip. 

    Regards,

    Joel H

  • The device is on our own board. As indicated in the problem statement there is no battery installed.

    Power_up_with_battery.jpg

    Vbus_to_RGEN.jpg

    Vbus_to_PMID.jpg

    Vbus_Current.jpg

  • Hey Roger,

    I have a few questions for your setup.

    Are you host (i2c) controlling your device or are you operating in standalone mode? If in host mode, have you read the register values out of start up? 

    Have you run the same test after disconnecting your LDO load? What current are you drawing from your load?

    Let me know your comments. 

    Regards,

    Joel H

  • Hey Roger,

    Could you also take a shot  of the switching waveform (SW pin) when the issue is occurring, specifically at the instance your Vsys rises up (in the us/div range)

    Thank you,

    Joel H

  • I have read the i2c registers after the microcontroller starts up, the registers contain the default values.

    I cannot easily disconnect the LDO however since the SYS pin is not powered the load should be zero.

    Overall stat up with SW pin

    SW pin at 1uS/div

  • Hey Roger,

    Could you please tell me the values of Registers REG08 and REG09? Those do not have default values. They are based on the system state. 

    Those will tell us what state the device think it's in before Vsys rises and after.

    These are the System Status and Fault registers. 

    Regards,

    Joel H

  • Hey Roger,

    Do you have a schematic of your system?

    Do you have an idea of the Total output capacitance on Vsys, that could be useful?

    The status register you read reveals a NTC Cold fault, which, if you have an NTC resistor attached to the device, could be triggered, but would be odd without a battery. However, a nuance of the part is latched fault conditions. Please make sure you read the registers twice during the duration of the issue to get the True fault, if any.


    Regards,
    Joel H
  • Total Capacitance is about 65uF all Ceramic

  • Hey Roger,

    I just have a few more questions and comments to see if we get closer to solution:

    Based on the status register values, you have a Tcold fault that comes from the TS pin/NTC. Try disabling removing your NTC or making sure the voltage on V_TS after REGN turns on is within the specified percentage of VREGN to put device in normal operating condition. 


    PMID is oscillating which could indicate a bad connection between your supply and VBUS. Make sure the connection is not loose or shaky. 


    Have you attempted to remove the secondary 3.3V load regulator and repeat the experiment?

    How are you performing DP and DM detection at the beginning.

     

    Regards,

    Joel H

  • Joel,

    Please keep in mind that there is no battery connected so no NTC is present. In addition the problem is that we don't get system power so we are not able to start Dp/Dm the charger is doing what ever is does with no supervision.

    The secondary regulator cannot be removed without damaging a VERY expensive PCB so I cannot try this. However since it has no input voltage until the battery charger comes up I doubt if this is the problem.

    The connection to Vbus seems solid, once the system processor gets power it monitors Vbus and the charger power good register value continuously , it does not report any issues.



    Roger

  • Unfortunately Roger,

    I was not able to duplicate the issue on our Evaluation Module, even with all the information you provided.

    The closest I was able to replicate was issue was with a lot of extra capacitance on Vsys (around 220uF), but that only adds around 200ms to our typical specification for startup, which is what you show in your waveforms. What adds the extra 300ms looks to be the oscillation on the PMID pin, which, without being stable, wont allow the internal regulator to startup.

    I would suggest you attempt to duplicate the issue on our EVM.

    If not, that would point to an issue in your system implementation of the chip or test setup.

    www.ti.com/tool/bq24297evm-021


    Regards,
    Joel H