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bq77910 Over Current Discharge Recovery (won't recover)

jonathan digiacomandrea
Prodigy 190 points

Community,

 

I am evaluating the first spin of a new design using the bq77910. I am having trouble recovering from an over current fault. The fault occurs as it should when I pull more than 120A out of the battery, but afterwards, no matter what I do I cannot get it to re-enable the DSG FET. I am using a series CHG DSG FET setup, and 8 cells. I have followed the data sheet and I will post my settings. I have tried toggling the CHGST line even though I don't have SOR enabled. 

 

 

; bq77910 Register File

; 10/3/2011 2:06:57 PM

01:44

02:22

03:42

04:B

05:C1

06:0

07:4

08:0

09:43

0A:33

 

 

I have a .0002Ohm sns Resistor. Let me know what other information you need to diagnose. Any Ideas?

 

Thanks,

JD

  • 0
    TI__Guru 54715 points

    Check that the DPCKN pin is going low.  Load removal is always required for SC/OC recovery regardless of SOR bit setting. A residual load on the PACK terminals may prevent DPCKN from falling sufficiently.

    Switching off a high current quickly can produce a high voltage from the inductive response of the cells and interconnect. It may be possible that the CPCKN pin is forced above BAT pin or other pins exceed their abs max during the transient sufficiently to cause damage and leakage that prevents load recovery.

    Check the device status after the fault by connecting the EVM GUI to the board if possible, or by reading with an I2C host. See  the data sheet for information, and http://e2e.ti.com/support/power_management/battery_management/w/design_notes/1409.aspx for register bit definition.  If a high voltage transient comes through the input filter, and exceeds abs max of the IC, inputs may be damaged and result in a permanent UV.

  • 0 in reply to WM5295
    Prodigy 190 points

    Thanks for the input! I found that I had neglected the R LDRM_DET resistor shown on page 32 of the datasheet in my layout. I have added a resistor for prototyping and it now works perfectly! Thank you so much for your help. The only issue I have left with the design is when a Short is applied the DSG FET literally explodes. I am able to apply a 400A discharge and the FET turns off without any problem, but a direct short blows it up. I am currently in the process of instrumenting it all and running an additional test to capture waveforms. I am guessing that since the cell stack has a total of 5.6mOhms of internal impedance the current is rising to well above 1000A and the inductive kick of the cables if over volting the source drain of the FET; causing a shoot through, then a short failure and eventually excessive heat, melting and explosion. I will update when I know more.

     

    Thanks again,

    JD