SLVAE57B February   2021  – October 2021 LM5050-1 , LM5050-2 , LM5051 , LM66100 , LM74202-Q1 , LM74500-Q1 , LM74610-Q1 , LM74700-Q1 , LM74720-Q1 , LM74721-Q1 , LM74722-Q1 , LM7480-Q1 , LM7481-Q1 , LM76202-Q1 , SM74611 , TPS2410 , TPS2411 , TPS2412 , TPS2413 , TPS2419


  1.   Trademarks
  2. Introduction
  3. Reverse Battery Protection
    1. 2.1 Reverse Battery Protection with Schottky Diode
  4. ORing Power Supplies
  5. Reverse Battery Protection using MOSFETs
    1. 4.1 Reverse Battery Protection using P-Channel MOSFET
    2. 4.2 Input Short or supply interruption
    3. 4.3 Diode Rectification During Line Disturbance
    4. 4.4 Reverse Battery Protection using N-Channel MOSFET
  6. Reverse Polarity Protection vs Reverse Current Blocking
    1. 5.1 Reverse Polarity Protection Controller vs. Ideal Diode Controller
    2. 5.2 Performance Comparison of P-Channel and Reverse Polarity Protection Controller Based Solution
  7. What is an Ideal Diode Controller?
    1. 6.1 Linear Regulation Control Vs Hysteretic ON/OFF Control
    2. 6.2 Low Forward Conduction Loss
    3. 6.3 Fast Reverse Recovery
    4. 6.4 Very Low Shutdown Current
    5. 6.5 Fast Load Transient Response
    6. 6.6 Additional Features in Ideal Diode Controllers
      1. 6.6.1 Back-to-Back FET Driving Ideal Diode Controllers
      2. 6.6.2 Very Low Quiescent Current
      3. 6.6.3 TVSless Operation
  8. Automotive Transient protection with Ideal Diode Controllers
    1. 7.1 LM74700-Q1 with N-Channel MOSFET
    2. 7.2 Static Reverse Polarity
    3. 7.3 Dynamic Reverse Polarity
    4. 7.4 Input Micro-Short
    5. 7.5 Diode Rectification of Supply Line disturbance
  9. ORing Power Supplies with Ideal Diode Controllers
  10. Integrated Ideal Diode Solution
  11. 10Summary
  12. 11References
  13. 12Revision History

Fast Reverse Recovery

During input supply failure or micro-short conditions, huge reverse current can flow into the input, discharging the load capacitors used for holdup. Ideal diode controllers feature a very fast reverse comparator and strong gate drive to pull down the gate to source voltage to turn OFF the MOSFET. The internal reverse comparator monitors the voltage across anode and cathode and if it exceeds the reverse current threshold, external MOSFETs gate is shorted to anode (source) with strong pulldown current. Reverse comparator delay and gate pulldown current determine how fast the MOSFET can be turned off. Total reverse current turn off delay includes reverse comparator delay and MOSFET turn off delay.

TI's ideal diode controller LM74700-Q1 features a very low reverse comparator delay of 0.75 µs maximum and gate pulldown current of 2.37A. A MOSFET with 5 nF of gate capacitance can be turned off within 0.75 µs + 21 ns = 0.77 µs, with 21 ns required to discharge 5 nF gate capacitance by 2.37 A of gate pulldown current. Figure 6-5 shows LM74700-Q1 reacting quickly within 0.77 µs to a short circuit at battery input. This prevents hold capacitors at the output from discharged into the shorted battery input line.

GUID-EC6FA837-015C-43D3-BE45-20FAAB0EA2D5-low.gifFigure 6-5 Input Short Circuit Response of LM74700-Q1