BQ76952: The drive of DSG MOSFET and the function of LD pin

GJ H

Part Number: BQ76952

Dear TI experts,

I have used your company's BQ76952 and encountered some issues.

1. When the LD pin is connected to the PACK through resistors （As shown in the following image）, the discharge MOS is not initially turned on, and the PACK+ is suspended. So, how does BQ76952 open the discharge MOS through the DSG pin?

2. I have learned that during the discharge MOS shutdown process, the voltage of the DSG pin will follow the changes of the LD pin. But, what is the role of the LD pin during the charging process? And if I ground the LD pin, how does the DSG pin turn on the discharge MOS?

When I quickly clicked on the power switch on the circuit board, I found that the PACK+ terminal had an output when the discharge MOS was not turned on. Therefore, I would like to know if this is related to the internal structure of AFE BQ76952.

Thanks！

10 months ago

0 Andria McIntyre 10 months ago

TI__Expert 8526 points

Hello,

In response to your questions:

1. Although you said "open the discharge MOSFET," the context makes me believe you mean to close the FET, or turn it ON. Please see Section 8 in the Multiple FET application note for more information on DSG FET turn on with respect to PACK+: Multiple FETs with the BQ76952, BQ76942 Battery Monitors (Rev. A).

2. If a charger is attached, then the BQ76952 can detect it because the voltage on the LD pin rises above the Vwakeonld threshold. The BQ76952 should be able to turn on the DSG FET due to the integrated charge pump. Please see the Multiple FET app note for more information on DSG driver turn-on and off functionality.

If you plan to use high side FETs, I recommend using the LD pin for its intended functions listed in the datasheet: BQ76952 3-Series to 16-Series High Accuracy Battery Monitor and Protector for Li-Ion, Li-Polymer, and LiFePO4 Battery Packs datasheet (Rev. B) (ti.com).

For more information on internal pin connects, see the Pin Equivalent Diagram app note: Pin Equivalent Diagrams for the BQ76952, BQ76942, and BQ769142 (ti.com). Unfortunately, I am not able to share more detail on inner workings of the device outside the simplified circuit diagrams in this app note.

Best,

Andria

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BQ76952: The drive of DSG MOSFET and the function of LD pin