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BQ40Z60: bq40z60 - Regarding hardware based protections

Venugopal S
Intellectual 640 points
Part Number: BQ40Z60

Section 2.8 of the Technical Reference Manual says that bq40z60 provides 3 hardware based protections - Overload in Discharge, Short Circuit in Charge, Short Circuit in Discharge.

My queries are as follows.

1) Why are these called HARDWARE based protections ?

2) What is the difference between hardware based and non-hardware based protections ?

3) What is the difference between Overload in Discharge (Section 2.8.1) and Overcurrent in Discharge (Section 2.6) ?

  • 0
    TI__Guru 73830 points

    The hardware based protections do not rely on interaction with the firmware. They cannot be disabled and can react very quickly to current faults such as short load and over current. You set the threshold and response time with the firmware and then these protections work independently of the firmware. The Overload in Discharge protection is hardware based and is triggers based on the voltage drop across the sense resistor. The Overcurrent in Discharge is controlled by the firmware as the firmware monitors that current reported by the coulomb counter. You have more flexibility in setting the detection thresholds and times with the firmware based protections.

  • 0 in reply to ThomasCosby
    Intellectual 640 points
    Thanks for your reply. I still have doubts in connection with some parts of your reply.

    1. "You set the threshold and response time with the firmware and then these protections work independently of the firmware."

    Since we are setting the response time and threshold in the firmware, how can we say that the protection is acting independently of the firmware or that there is no interaction with the firmware? Doesn't setting the parameters imply interaction ? Still the system has to rely on values entered into these parameters in the firmware for protection, right?

    2. "The Overcurrent in Discharge is controlled by the firmware as the firmware monitors that current reported by the coulomb counter."

    Ultimately isn't the coulomb counter also measuring current by measuring the voltage drop across the sense resistor ? If yes, then the working principle will be same as in overload in discharge. If no, how else is the coulomb counter measuring current?
  • 0 in reply to Venugopal S
    TI__Guru 73830 points
    When you update the parameters for the hardware based parameters. then you have to reset the device to allow them to take effect. The gauge writes them registers in the AFE and they not no longer interact with the firmware.

    The coulomb counter does calculate coulombs and current by measuring the voltage drop across the sense resistor. It accumulates coulombs over a 250ms window and then converts it. It averages four of these windows and updates the current every 1s. So, the gauge cannot respond fast enough to a shorted load condition to protect the FETs, using this interface. The hardware interface monitors the voltage drop across the sense resistor directly and can respond microseconds to protect the FETs.