SLYT863 April   2025 LM5066I

 

  1.   1
  2. 1 Introduction
  3. 2 3
  4. 3 Challenges in designing a hot-swap circuit for a 48V AI server
  5. 4 Challenge No. 1: Turnoff delay during an output short-circuit
  6. 5 Challenge No. 2: False gate turn-off during a load transient
  7. 6 Challenge No. 3: Parallel resonance during controlled (slow) turn-on
  8. 7 Proposed circuit enhancements
  9. 8 Improving the turn-off response
  10. 9 Overcoming false turn-off for dynamic loads
  11. 10Damping parasitic oscillations
  12. 11Design guidelines and component selection
  13. 12Cdv/dt discharge circuit
  14. 13Conclusion
  15. 14References
  16. 15Related Websites

8 Improving the turn-off response

In the proposed solution shown in Figure 8, introducing an external fast pull-down circuit using - PNP transistor (QPD and RPD) will boost up the turn-off speed. During an output short-circuit event, the gate pull-down current of 160mA creates a substantial voltage drop across the RPD resistor and enables fast pull-down of the PNP transistor (QPD). This in turn shorts the gate-to-source of all parallel MOSFETs, turning off the MOSFETs immediately to quickly disconnect the power path. Figure 9 shows the experimental result for a short-circuit event with a fast pull-down circuit.