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Original question:

[FAQ] BQ25890: [FAQ] BQ2589X: Schematic Review and PCB Layout Design Tips

BQ25895: PMIC getting exceptionally hot when suppied via USB

Craig Easdale
Expert 2180 points
Part Number: BQ25895


Tool/software:

I have implemented a BQ25895 in my design with plans to make use of it's PMID output as the main 5V power supply for my USB/battery-powered instrument.

On powering up the system for the first time I have noticed that the BQ25895 gets exceptionally hot, drawing 1.5A+.

To try to isolate the problem I have done the following;

  • Isolated the PMIC output from the 3V3 regulator supply (removing power from controller and various other downstream components)
  • Disconnected the battery

After doing this there are only a couple of idle parts (power gates) on the PMID pin output (both of which are disabled), but the IC still gets very hot.

I took some measurements on the outputs:

  • PMID: 3.1V 
  • VSYS: 2.6V

When creating my design I tried to adhere to the "BQ25895 Schematic Checklist" document, so I'm not really sure if/where I've gone wrong to cause this issue. Is there a chance 

If someone could cast any eye over and offer some suggestions that would be appreciated.

  • 0
    TI__Mastermind 32520 points

    Hi Craig, 

    We are looking into your inquiry and will provide an update by the end of the day today US time. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    TI__Mastermind 32520 points

    Hi Craig, 

    I have reviewed your schematic and see no clear issue. You have all necessary components. 

    In terms of next steps of debug measurements of PMID = 3.1V and VSYS = 2.6V with a 5V input at VBUS is not expected. Have you verified there is actually 5V present at VBUS pin? There is only 1 FET between VBUS and PMID (as shown in function block diagram on datasheet page 14) so with 5V applied PMID is expected to measure close to 5V as well. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Expert 2180 points

    Hi Garrett, 

    Thanks for your reply. After some tinker it seems that there had possible been an issue in manufacture. Remvoing the diode (D13) seemed to have rectified the overheating issue.

    Without a battery connected, PMID is now sitting pretty close to VBUS.

    I've noticed another problem, however, this time with VBAT and as a result,VSYS..

    I have a single-cell 2800mAh Li-ion battery which has a voltage of 3.85V when unconnected. However, when I connect this to the system the reading at VBAT is 0.62V with USB power connected to VBUS, and 0.95V without power at VBUS. There is ~50mV at VSYS.

    • I have changed the STAT LED source to the 3V3 derived from PMID - when VBUS has power the STAT LED is static
    • I have confirmed the !CE pin is low
    • The BQ25895 is running with all the defaul configuration

    Any idea what's going on here? Does it require specific configuration to perform the most basic battery related functions?

  • 0 in reply to Craig Easdale
    TI__Guru 59491 points

    Hi,

    What are all the register readings for each case?

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 10 points

    Hey Ning,

    When powered from a 5V USB supply we read the following data from the registers

    reg 00 = 48,
    reg 01 = 5,
    reg 02 = 3d,
    reg 03 = 3a,
    reg 04 = 20,
    reg 05 = 13,
    reg 06 = 5e,
    reg 07 = 9d,
    reg 08 = 3,
    reg 09 = 44,
    reg 0A = 93,
    reg 0B = af,
    reg 0C = 0,
    reg 0D = 13,
    reg 0E = 0,
    reg 0F = 0,
    reg 10 = 0,
    reg 11 = 98,
    reg 12 = 0,
    reg 13 = 42,
    reg 14 = 39
    With only the battery connected we read.
    reg 00 = 48,
    reg 01 = 5,
    reg 02 = 3d,
    reg 03 = 3a,
    reg 04 = 20,
    reg 05 = 13,
    reg 06 = 5e,
    reg 07 = 9d,
    reg 08 = 3,
    reg 09 = 64,
    reg 0A = 93,
    reg 0B = 2,
    reg 0C = 0,
    reg 0D = 13,
    reg 0E = 0,
    reg 0F = 0,
    reg 10 = 0,
    reg 11 = 0,
    reg 12 = 0,
    reg 13 = 8,
    reg 14 = 39
  • 0 in reply to Liam
    TI__Guru 59491 points

    Hi,

    We will check and get back to you soon.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Expert 2180 points

    Hello Ning, did you manage to take a look at this?

    Thanks,
    Craig

  • 0 in reply to Craig Easdale
    TI__Mastermind 32520 points

    Hi Craig, 

    The majority of our team was out late last week for the US holiday. I will work to review and provide an update today or tomorrow. Thank you for your patience. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    TI__Mastermind 32520 points

    Hi Craig, 

    Please see my comments below. 

    Craig Easdale said:
    Does it require specific configuration to perform the most basic battery related functions?

    The BQ25895 does not require specific configuration to perform charging assuming CE is low as you have verified. 

    In my opinion the first step to debug should be to determine why your battery voltage does not match expectation. To simplify the test can you start with only the battery connected and disable OTG boost mode by pulling OTG pin to GND (or disable OTG via I2C REG03[5] = 0). In this state battery should directly power SYS output. 

    The 'with only battery connected' register log showed BATFET_DIS (REG09[5]) bit set to 1. This is potentially due to the low battery voltage measured at VBAT and attempting to start boost mode. With boost mode disabled REG09 bit 5 should remain 0. 

    If voltage measured at BAT and SYS pin of BQ25895 is still much lower than expectation with boost mode disabled then it appears you have some hardware issue along the path from battery terminal to charger IC. 

    Best Regards,

    Garrett