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

Reverse Polarity Protection vs Reverse Current Blocking

Reverse battery protection involves two aspects of protection, commonly referred to as reverse polarity protection (RPP) and reverse current blocking (RCB). Reverse polarity protection, also referred to as reverse hookup protection (RHP), prevents the load from getting damaged due to negative voltage at the input during a reversely connected battery or dynamic reverse polarity conditions during a inductive load disconnect from battery. Reverse polarity protection does not necessarily block reverse current flowing into the battery from the load or downstream DC/DC converters. In many automotive subsystems, large holdup capacitors are used to provide sufficient back up power during a short interruption of battery line or shorted battery input, so that the subsystem can function uninterrupted or perform maintenance housekeeping tasks such as memory dump before turning off. Reverse current blocking prevents reverse current from flowing back into the battery from the load and allows holdup capacitors to provide additional back up time for the subsystem to function during various dynamic reverse battery conditions or short interruptions.

One key difference between battery protection using schottky diode and protection using P-Channel MOSFET is the schottky diode blocks reverse current flowing from the load back into the battery all the time and inherently provides both reverse polarity protection and reverse current blocking. When the battery is connected with its terminal reversed, the schottky diode gets reverse biased and blocks reverse current from discharging the holdup capacitors connected to the load. This naturally isolates the load from the negative input voltage and provides reverse polarity protection to the load.

The battery protection shown in Figure 4-1 or in Figure 4-8 does not block reverse current from flowing back into the battery since the MOSFETs are turned off when the battery voltage is close the Vth of the MOSFETs and not as soon as the battery voltage starts to drop. During a input micro-short at the battery, holdup capacitors can be discharged to a voltage lower than the downstream DC/DC converters UVLO, leading to reset of the subsystem.