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BQ25120A: Upon power application Vsys only rises to 1V

Evan Dougal25
Prodigy 40 points
Part Number: BQ25120A

Some of our prototypes have entered a state where the BQ25120A will raise VSYS to 1.8V for a brief moment (spike lasts 10us), and then the voltage on VSYS rises only to 1V. These devices have previously booted successfully, and other devices are still working with the same software.

No I2C messages have been sent at this point because our MCU does not boot. 

Power cycling the device (removing both battery and USB) has no effect (i.e. the device stays in this state). 

Sounds like a similar issue to this one here, but I don't see an answer: 

https://e2e.ti.com/support/power_management/battery_management/f/179/p/626295/2319419?pi317195=1

Yellow is VBUS from the USB. Blue is VSYS. The voltage spike is barely visible in the first image, see image two for a close up (note the differences in time scale).  

  • 0
    TI__Genius 12485 points

    Evan,

    Can you please post your schematic? Also where did you get the units from?

    regards,

    gautham

  • 0 in reply to Gautham
    Prodigy 40 points

    Here is the BQ25120a portion of the schematic: 

    The parts were samples from TI.

    One other thing to note is that the ~MR hard reset does not appear to do anything. 

  • 0 in reply to Evan Dougal25
    TI__Genius 12485 points
    Evan,

    Schematic looks okay. The puzzle here is why is VSYS trying to start back up really slow. What is the total capacitance on 1.8V rail?

    On the plot1, is battery connected? The VIN itself seems to chatter around 5.5-5.6V if you look closely. That is close to the OVP threshold.

    Are you able to startup with a DC supply with voltage bumped down a bit?

    On the /MR, since the default for the BQ25120A is to go to hiZ Mode, you wont see it trying to restart. If that bit was set to go to Ship Mode, then it will shut down.

    With the I2C bus not being able to be powered, that won't be possible.

    Also please share scope plots of PMID with relative to VBAT as well.

    thanks,
    gautham
  • 0 in reply to Gautham
    Prodigy 40 points

    Hi Gautham,

    Right now we do not have a battery installed in the device. 

    Based on the decoupling capacitors on the line, the capacitance on VSYS looks to be ~20uF. 

    The battery is not connected. I took a closer look at VIN and it looks like the highest peak while it's ringing reaches 5.6, then stabilizes at around 5.1V. I will attempt to boot the device directly from a controlled power supply.  

    Here is a plot with VBUS, VSYS, and PMID:

    Yellow: VBUS

    Pink: PMID

    Blue: VSYS

    PMID rises to ~750mV, but no further. 

  • 0 in reply to Evan Dougal25
    TI__Genius 12485 points

    Evan,

    You will need to install a battery or a powersupply on the BAT pin so that /MR can function. /MR is pulled up to VBAT internally. 

    Please try that method as well. 

    thanks,

    gautham

  • 0 in reply to Gautham
    Prodigy 40 points

    Hi Gautham,

    I have tried all of this with a battery. When a battery is connected VSYS only rises to ~100mV.

    Evan