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BQ40Z60, DSG won't turn on

Jim OSullivan
Intellectual 375 points
Other Parts Discussed in Thread: BQ40Z60

Hi,

I'm bringing up a custom PCB based on the bq40z60.  It's essentially the EVM circuit but with the secondary protection IC and fuse removed.  It's being used with a 3S LiPo battery and a ~16.7V "VAC" source.  I've been unable to get the DSG FET to remain on and provide power to the system.  The load is small - about 40mA.

Attached is a screen shot and a gg.csv file.  I'd appreciate it if someone could take a look and point out anything misconfigured that I've missed.


Thanks.

Initial.gg.zip

  • 0
    TI__Guru 73830 points

    Jim

    The AOLD fault is preventing the DSG FET from turning on. I checked your gg file and there is not a parameter setup problem. You will need to check the voltage between SRP and SRN on the device to make sure that there is not a voltage causing the gauge to think that an over load condition is present. 

    tom

  • 0 in reply to ThomasCosby
    Intellectual 375 points

    Hi Tom,

    On further investigation, it appears the fault is real.  The 40q60 is turning on the Discharge FET at the same time as it turns on the Low-side FET, creating a path to ground through L1.  It shuts off after 30ms, but the inductor is still getting hot.

    Is it expected that the 40z60 would be turning on the low-side FET at the same time as the Discharge FET?

    Thanks.

  • 0 in reply to Jim OSullivan
    TI__Guru 73830 points
    There should be some dead time between the signals, but I seem to recall that it is smaller for one edge. Do you have fairly sharp transition times? What is the saturation current rating for your inductor?
  • 0 in reply to ThomasCosby
    Intellectual 375 points

    LODRV (green trace) and DSG (blue trace) are shown in the image below.  L1 has a saturation current of 2.5A, chosen based on a charging current of 1A and a ripple current of ~0.4A.