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BQ76952: BQ76952

Yebohr Zhao
Prodigy 285 points
Part Number: BQ76952

1_Multiple FETs with the BQ76952 BQ76942_.pdf

Hi   Team

Question1:   For the attachment is a application Report.  the customer has referred to one of the circuits, as shown in the right figure,  however, the customer is not familiar with the function of Q32, so they would like to ask how Q32 works. 

the circuit designed by the customer is shown in the following figure, and they would like to know how Q36 works.

Question2: How does the LD Pin of BQ76952 work? Can the LD perform normal load detection? for example, if the system is connected to a load, can the LD Pin detect the load and wake up the AFE for discharge.

                  (i see the datasheet that LD will be used to short circuit protection. so i want to know that Can the LD perform normal load detection.)  Have you seen the methods commonly used for load detection?

Best Regards

Yebohr zhao

  • 0
    TI__Expert 4085 points

    Dear Yebohr,

    1. For Q32, the PFET allows a reverse charge circuit to exist.  The PFET will be on when DSG rises and as DSG falls to allow R40 to drain the excess discharge gate capacitance. However, once it is discharged, the PFET will turn off, meaning the gate pull down resistor, R41, to be disabled as the DSG node will be higher than the other side of the D7 diode. For more information on Q32's purpose, view page 20 of Multiple FETs with the BQ769x2 Battery Monitors. Looking at Q36, it seems like that should be a similar purpose, but I'd need to see the full schematic.

    2. When the LD pin has a voltage across it that exceeds the threshold set, the device will begin a wakeup sequence which includes waking up the FETs. This can be seen in Table 16-2 in the datasheet. Is there something else you wish to do with load detection?

    Best,

    Asher Nederveld

  • 0 in reply to Asher Nederveld
    TI__Prodigy 285 points

    Hi  Asher Nederveld

    thanks for your explanation.  

    1: i see the application report,  the  Q29 clams the gate stage and source electrode of the discharge MOS together, while Q32 is used to prevent the pack+ from being pulled down below VSS when the charger is reversed, preventing DSG from being damaged due to pulling current. (thanks for your explanation, please correct me if i understand is fault)

    2: The LD Pin can use to wake up AFE from shutdown mode to normal. this type of wake-up requires applying a voltage to the LD Pin.  if AFE in shutdown mode, load detection must be carried out through an additional circuit, and then the AFE is awakened for discharge.  i want to know if the load detection function is enabled when AFE is in sleep mode, will AFE automatically wake up when the load is connected?

    Best Regards

    Yebohr zhao

  • 0 in reply to Yebohr Zhao
    TI__Expert 4085 points

    Dear Yebohr,

    Your understanding seems to be correct for 1. 

    As for as the LD pin for SLEEP, the AFE should wake up when a charger is detected via the LD pin on the device. Likewise, when a large enough current is detected to be flowing, it will also exit SLEEP mode. Figure 7-1 in the Technical Reference Manual should help you understand the transition from state to state. Are you operating in source-follower mode? If not, the DSG FET should stay on while in SLEEP mode so the current would most likely wake the device up first when a load is activated.

    Best,

    Asher Nederveld