SLUAB39 January   2026 BQ76905 , BQ76907 , BQ769142 , BQ76920 , BQ76930 , BQ76940 , BQ76942 , BQ76952 , BQ76972

 

  1.   1
  2.   Abstract
  3. 1Introduction to the low-side/high-side protection solutions
  4. 2Short-circuit protection results in overvoltage damage to DFET
    1. 2.1 Low-side protection solution
    2. 2.2 High-side protection solution
    3. 2.3 Summary
  5. 3Short-circuit protection results in overtemperature damage to DFET
    1. 3.1 Low-side protection solution
    2. 3.2 High-side protection solution
    3. 3.3 Summary
  6. 4Conclusion
  7. 5References

3.1 Low-side protection solution

For the low-side protection solution, taking BQ76940 as an example, G-pole voltage, VG, is clamped around -0.3V by the built-in diode at the shutdown instant of DFET. S-pole voltage, VS, is clamped at BAT-, also equal to 0V.

Low-side protection solution-the discharge tube DFET shutdown equivalent circuitFigure 3-4 Low-side protection solution-the discharge tube DFET shutdown equivalent circuit

Figure 3-5 shows BQ76940 DSG Pin equivalent circuit. When AFE turns off DFET, DSG Pin pulls to ground through RDSG_OFF inside AFE, so the shutdown time depends only on the junction capacitance of DFET and the discharge resistor RDSG_OFF=2.5KOhm.

When G-pole voltage of DFET drops to meet the following conditions, DFET can be turned off completely.

Equation 6. V G < V G S t h D F E T
BQ76940 DSG pin equivalent diagramFigure 3-5 BQ76940 DSG pin equivalent diagram

Naturally, the users may further regulate the shutdown speed by placing an additional resistor between DSG pin and G-pole of DFET.