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. 1 Introduction
  3. 2 Reverse Battery Protection
    1. 2.1 Reverse Battery Protection with Schottky Diode
  4. 3 ORing Power Supplies
  5. 4 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. 5 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. 6 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. 7 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. 8 ORing Power Supplies with Ideal Diode Controllers
  10. 9 Integrated Ideal Diode Solution
  11. 10Summary
  12. 11References
  13. 12Revision History

6.2 Low Forward Conduction Loss

Forward voltage drop of schottky diodes increases the forward conduction power loss and requires thermal management using heat sink and requires PCB space leading to increased cost. Ideal diode controllers use an external MOSFET to reduce the forward voltage to 20 mV or lower, depending on the control scheme. Linear regulation control scheme maintains 20 mV forward voltage during most of the operating current range. Hysteretic ON/OFF control fully enhances the MOSFET to reduce the forward voltage and the forward drop is decided solely based on the MOSFET used.

Forward voltage of the MOSFET DMT6007LFG driven by ideal diode controller is compared against forward voltage of schottky diode STPS20M60S in Figure 6-3. An ideal diode controller using linear regulation scheme regulates the forward voltage to low 20 mV up to load current = 20 mV / RDS(MIN) and load current higher than 20 mV / RDS(MIN) forward voltage solely depends on MOSFETs RRD(ON). In Figure 6-3, MOSFET is regulated to 20 mV forward voltage up to 5.7 A and beyond 5.7, a MOSFET is fully enhanced and forward voltage increases based on load current. At 10 A, low forward voltage drop is reduced to 35 mV against 465 mV using a Schottky diode. LM74722-Q1 ideal diode controller offers an even lower forward voltage drop of 13 mV, providing further improvement in power efficiency.

GUID-B89C54CF-52FA-44B4-AE65-884F91C605CC-low.gifFigure 6-3 Forward Voltage Vs Load Current
GUID-EE72C78B-C7D2-42E8-B11A-288EC2194689-low.gifFigure 6-4 Power Dissipation Vs Load Current

Figure 6-4 shows the power dissipation comparison between schottky diode and ideal diode controller. At a 10 A load current, DMT6005LPS-13 MOSFET dissipates 0.35 W of power, whereas schottky diode STPS20M60S dissipates 4.65 W of power leading to more than 10x power saving when using ideal diode controller and MOSFET.