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

ORing Power Supplies with Ideal Diode Controllers

The LM74700-Q1 combined with external N-Channel MOSFETs can be used in OR-ing Solution as shown in Figure 8-1. The forward diode drop is reduced as the external N-Channel MOSFET is turned ON during normal operation. The LM74700-Q1 quickly detects the reverse current and quickly pulls down the MOSFET gate, leaving the body diode of the MOSFET to block the reverse current flow.

GUID-4C6F2AE0-6CD5-4B9D-91F1-10A467A8E1EB-low.gif Figure 8-1 Typical OR-ing Application

An effective OR-ing solution needs to be extremely fast to limit the reverse current amount and duration. The LM74700-Q1 devices in an OR-ing configuration constantly sense the voltage difference between anode and cathode pins, which are the voltage levels at the power sources (VIN1, VIN2) and the common load point respectively. The source to drain voltage VDS of the MOSFET is monitored by the anode and cathode pins of the LM74700-Q1. A fast comparator shuts down the gate drive through a fast pulldown within 0.75 μs (typical) as soon as V(IN) – V(OUT) falls below –11 mV. It turns on the gate with 11 mA gate charge current once the differential forward voltage V(IN) – V(OUT) exceeds 50 mV.

Time (5 ms/DIV)
Figure 8-2 ORing VIN1 to VIN2 Switch Over
Time (5 ms/DIV)
Figure 8-4 ORing VIN2 to VIN1 Switch Over
Time (5 ms/DIV)
Figure 8-6 ORing - VIN2 Failure and Switch Over to VIN1
Time (5 ms/DIV)
Figure 8-3 ORing VIN1 to VIN2 Switch Over
Time (5 ms/DIV)
Figure 8-5 ORing VIN2 to VIN1 Switch Over
Time (10 ms/DIV)
Figure 8-7 ORing - VIN2 Failure and Switch Over to VIN1

Figure 8-2 to Figure 8-5 show the smooth switch over between two power supply rails VIN1 at 12 V and VIN2 at 15 V. Figure 8-6 and Figure 8-7 illustrate the performance when VIN2 fails. The LM74700-Q1 controlling VIN2 power rail turns off quickly, so that the output remains uninterrupted and VIN1 is protected from VIN2 failure.

Power dissipation and its associated thermal management issues of using a schottky diode are minimized due to the low forward voltage drop of ideal diode controllers. MOSFETs do not have leakage currents as high as a schottky diode at high temperatures and using MOSFETs reduces the reverse leakage loss. This improves overall efficiency and reliability of the system.

Load sharing concerns due to schottky diode difference in forward voltage and its negative temperature co-efficient are not present when using ideal diode controllers. Further, the linear regulation of forward voltage drop enhances load sharing between power supplies.