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bq20z45 AFE OC Dsg not working

ed kornegay
Intellectual 280 points
Other Parts Discussed in Thread: BQ20Z40

I am looking at SLUA511B "Configuring the bq20z40/bq20z45 Data Flash".  On page 7 it explains how the AFE OC Dsg register works and the values it will take.

I set the value to 0x00.  According to the table on page 7, that means the OC protection will trigger when the AFE sees 50mV.  On my system, with a 0.011 Ohm sense resistor, that's 4.54A I think (50mV / 11mOhm).

I set my electronic load for 5A, but the OC protection does not trigger.  AFE OC Dsg Time Configuration is set for 0x0f (31mS).  In 2 seconds, the 1st level protection triggers (it is set for 2A).

If I read the voltage across the sense resistor with a DMM. I see the expected 55mV, which should trigger the AFE.  (Actually I see -55mV, positive lead on ASRP, negative lead on ASRN.  Does that matter?)

I set the OC Dsg register to 0x01, adjusted values and tried again - same result.

What am I missing?

Thanks

Ed K

  • 0
    TI__Intellectual 2650 points

    What have you set AFE OSG DSG Time to ?  0x00 to 0x0F seem to be the recommended range, with >0x0F producing unpredictable results.

    After you make setting changes are you are sending an 0x41 reset to make sure all the changes take effect ?

    Mike

  • 0 in reply to Mike Ewer
    Intellectual 280 points

    Thanks for the reply.

    I just tried the reset, and that did not change anything.  However, I discovered that a power cycle does have an effect.  Just pulling the battery then waking up the z45 again makes the new value take effect.  

    Not sure if it's supposed to happen that way, but unless you have some advice I'll take it.

    Thanks for pointing me in that direction.

  • 0 in reply to ed kornegay
    TI__Intellectual 2650 points

    That is good news. The app note section on AFE OC DSG  refers to important note at start of Current section which is on page 4, copied  here and that talks about the need for a reset to transfer data to AFE

    I also recalled a colleague previously mentioned the AFE needs a reset when changes are made although I could not recall what type of reset and the text above does not make that very clear. I guess the 0x41 only resets the gauge in the micro while the AFE is a seperate block and so must need a POR.