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

9 Overcoming false turn-off for dynamic loads

In this solution, the hot-swap gate node is decoupled from the MOSFET gate terminal by placing the DSS diode between them, again shown in Figure 8. This modification helps eliminate the reflection of output voltage ripple to the hot-swap controller GATE node and avoids false turn-on of the soft-start PNP transistor, Qss. Changing the position of the diode does not impact controller behavior during start-up nor any of the fault events. As shown in the test result (see Figure 10), the system operates continuously even for large load steps from 20A to 120A at a 1kHz frequency.

Proposed hot-swap circuit configuration. Figure 8 Proposed hot-swap circuit configuration.
Output short-circuit response with fast pull-down circuit. Figure 9 Output short-circuit response with fast pull-down circuit.
Load transient performance for steps from 20A to 120A to 20A at a 1kHz frequency. Figure 10 Load transient performance for steps from 20A to 120A to 20A at a 1kHz frequency.