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bq40z60 : Precharge Timeout Protection

Venugopal S
Intellectual 640 points

In Table 2.17 in SLUUA04C, the condition for "Enable" status is Current() > PTO:Charge Threshold AND ChargingStatus[PV] = 1.

The default value for PTO: Charge Threshold is given as 2000mA.

However, in Precharge Data Flash (4.9.1) ,the precharging current default is 250mA. If the precharging current is set at 250 mA, how and when will Current() become greater than or equal to 2000mA.

How does the PTO Timer work and what is the purpose of this protection ?

  • 0
    TI__Guru 73830 points

    This is a configuration mistake in the TRM and device. The default Charge Threshold should be 200mA and the Suspend Threshold should be 180 mA.

  • 0 in reply to ThomasCosby
    Intellectual 640 points

    Thank you for the info. Further, I have another doubt regarding the same.

    1) Enable :- Current() > PTO:Precharge Threshold AND Charging Status[PV] = 1 -------------------------- Start Timer

    2) Suspend :- Current() < PTO:Suspend Threshold  --------------------------------- Stop Timer

    3) Trip :- PTO timer > PTO:Delay ------------------------------ OperationStatus[XCHG] = 1

    Consider a scenario. My battery is in Precharge mode, charging with a current of 250 mA. This satisfies condition 1. Timer will start now. After a certain time (less than 1800s), the battery goes into low voltage constant current charging mode, charging with a current of 2000 mA. And the charging cycle progresses in the normal fashion. In this sequence, nowhere are we meeting the condition for stopping the timer, which is  condition no.2.

    Will the timer continue running even after we exit from Precharge mode and if so, will it trip the charging MOSFET after 1800s of charging?

  • 0 in reply to Venugopal S
    TI__Guru 73830 points
    If you are still in pre-charge mode (PV=1) when the current increases to 2000mA, then the gauge should declare a Precharge Over-current fault and halt charging. The PTO timer would continue to run as long as the charging current it present.
  • 0 in reply to ThomasCosby
    Intellectual 640 points
    I was talking about exiting Precharge mode into Constant Current mode (2000mA). In that case, will the PTO Timer continue to run? To simplify, if my charging operation is normal, and if it enters Constant Current mode after spending little time in Precharge mode, how will the PTO timer stop ?