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Original question:

BQ78350-R2-DEVICE-FW: Pre-discharge on low side ?

BQ78350-R2-DEVICE-FW: Pre-discharge, Algorithm

LOIC REBOUSSIN
Expert 1620 points

Part Number: BQ78350-R2-DEVICE-FW

Hi All,

I'm using a standalone system with a BQ78350-R2 and her AFE but without µC for communicate. How I can using Pre-discharge?

Today I was tried to use it but the pre-discharge is only activated when I send the Reset command. When I sent the Reset command the DSG-FET trigged to OFF and so PDSG-FET trigged to ON during 10s.

In fact I want to have DSG-FET in OFF with PDSG-FET ON when GG is in Sleep Mode. Whan the GG detect charging current (Normal MODE), the PDSG-FET stay 10s and after that only DSG-FET is ON. What parameters can I do change for make that?

Best regards,

Loïc

  • 0
    TI__Prodigy 590 points

    Hello Loic

    Pre-discharge is new function supporting in BQ78350-R2 FW version, the TRM has detail description for this feature in section 3.1, you could refer to the link below. http://www.ti.com/lit/ug/sluubm6/sluubm6.pdf

    Please check the Charge Current Threshold, FET ON TIME and FET option configuration following the link above eif have right setting regarding to you application and requirement. 

    Thank you

  • 0 in reply to Jessica LI
    Expert 1620 points

    Hi Jessica,

    Thank you for your answer but my issue is about TRM for R2 (SLUUBM6). The section 3.1 specify that PDSG works when DSG fet is OFF but in my case DSG fet is OFF only when Fault occurs so I haven't never Pre-discharge mode.

    => Predischarge mode only occurs after a RESET.

    => How can I activated predischarge mode in Relax mode or Sleep mode ?

    Thank you for your help,

    BR,

    LOIC

  • 0 in reply to LOIC REBOUSSIN
    TI__Guru 54715 points

    Hi LOIC,

    The pre-discharge mode is a transient mode intended to charge a large system capacitance from the battery through a resistance without creating a OCD or SCD event.  It is active before the discharge FET is turned on for the time Pre-Discharge:[FET ON Time].  If you have not turned off the DSG FET then pre-discharge mode can not be entered.

    Pre-discharge mode is not a gauging or battery state but the temporary transition described.  It cannot be set in sleep mode or relax mode unless the discharge FET is transitioning.

  • 0 in reply to WM5295
    Expert 1620 points

    Hi WM5295,

    As I understand it unlike the precharge I can not use the pre-discharge without SMBus communication ?

  • 0 in reply to LOIC REBOUSSIN
    TI__Guru 54715 points

    Hi Loic,

    Pre-discharge will work in the same mode without SMBus communication.  It does not change its mode or operation without SMBus.  But it won't go into a mode with pre-discharge set continuously in sleep. 

  • 0 in reply to WM5295
    Expert 1620 points

    Hi WM5295,

    Thanks for your answer but my issue is that PDSG works when the DSG fet is off. But during normal operation (no load, no discharge), the DSG fet is disabled only when a fault occurs, so that I never have the Pre-discharge mode before discharge.

    Loïc

     

  • 0 in reply to LOIC REBOUSSIN
    TI__Guru 54715 points

    Hi Loic,

    Right,  DSG is normally on which will keep the PACK voltage present in the system, so pre-discharge is not needed.

    If there is a fault DSG goes off and the PACK voltage in the system will fall.  On recovery from the fault the high capacitance of the system could trigger SCD each time recovery is attempted, so PDSG is on for a time to allow the battery to charge that capacitance at a limited current before DSG comes on.  The only time PDSG will be on is preceeding the transition of DSG from off to on.  Once DSG is on current can flow from the battery when needed, it does not need PDSG to transition.