• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 199 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ76952: PCHG and PDSG FETs turn-on sequence

Kyungjae Lee
Intellectual 660 points
Part Number: BQ76952

Tool/software:

Hi,

I'm currently working on enabling the PRECHARGE and PREDISCHARGE modes on the AFE used for our BMS.

Suppose that the PRECHARGE and PREDISCHARGE modes are enabled by setting the related parameters. When there are no faults and no current is flowing through the BMS, the FET status is as follows:

  • CHG FET: closed, PCHG FET: open
  • DSG FET: closed, PDSG FET: open

My questions are as follows:

  1. If the battery starts discharging at a current higher in magnitude than the Settings:Current Thresholds:Dsg Current Threshold value, will the AFE immediately open the previously closed DSG FET and close the previously open PDSG FET to perform pre-discharge?

  2. Likewise, if the battery, whose cell voltage is below the Settings:FET:Precharge Start Voltage, starts charging at a current higher than the Settings:Current Thresholds:Chg Current Threshold value, will the AFE immediately open the previously closed CHG FET and close the previously open PCHG FET to perform precharge?

Thank you,

Kyungjae Lee

  • 0
    TI__Mastermind 18025 points

    Hello Kyungjae,

    If the DSG FET is already active/ON, the PDSG FET won’t be activated unless the DSG FET is turned off and on again (this can be done through commands). This should be likewise with the PCHG FET.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Intellectual 660 points

    Hi Alexis,

    So, would it be logical to say that the following two conditions are required to observe the PREDISCHARGE mode?

    1. DSG FET: OFF

    2. The load is ready to be charged once either the DSG FET or PDSG FET is ON.

    My understanding of what you said is that only when the above two conditions are met and the AFE is ready to turn on the DSG FET (e.g., recovering from a fault condition), the PDSG will turn on first, followed by the DSG FET turning on. Is this correct?

    In other words, I wouldn't be able to observe the PREDISCHARGE mode when the load starts charging, while the AFE has already kept the DSG FET ON (because there's no fault). Is this correct as well?

    Thank you,

    Kyungjae Lee

  • 0 in reply to Kyungjae Lee
    TI__Mastermind 18025 points

    Hello Kyungjae,

    Thank you for your patience. 

    Kyungjae Lee said:
    My understanding of what you said is that only when the above two conditions are met and the AFE is ready to turn on the DSG FET (e.g., recovering from a fault condition), the PDSG will turn on first, followed by the DSG FET turning on. Is this correct?

    Those conditions should be correct to observe PREDISCHARGE mode.  

    Kyungjae Lee said:
    In other words, I wouldn't be able to observe the PREDISCHARGE mode when the load starts charging, while the AFE has already kept the DSG FET ON (because there's no fault). Is this correct as well?

    That is correct. This previous post may also be useful to refer too: Predischarge Corner Case in Fully Autonomous Mode. 

    Best Regards,
    Alexis