SLYT818 November   2021 LM74701-Q1 , LM74721-Q1

 

  1. 1 Introduction
  2. 2 Automotive reverse-battery protection with ideal diode controllers
  3. 3 TVS-less automotive reverse-polarity protection using ideal diode controllers
  4. 4 TVS-less ideal diode: mode of operation and working principle
  5. 5 External MOSFET
  6. 6 Output Capacitor (COUT)
  7. 7 TVS-less ideal diode controller EMC performance
  8. 8 Conclusion
  9. 9 Related Websites
  10. 10Important Notice

6 Output Capacitor (COUT)

During an ISO7637-2 Pulse 1 event with a TVS-less ideal diode controller, current flows from the output capacitor back to the input source, discharging the output voltage. The output voltage can swing negative if the output capacitor is not large enough to hold the voltage above 0 V. An ideal diode controller such as the LM74701-Q1 is capable of handling negative voltages on the output (the cathode pin) and can work with lower-output capacitors. However, if the loads connected at the output of an ideal diode controller – such as DC/DC converters, audio amplifiers and voltage regulators – are not capable of handling a negative input voltage, then you must scale the output capacitor such that the output voltage does not go below 0 V during an ISO 7637-2 Pulse 1 transient event.

Equation 3 calculates the minimum required output capacitor during an ISO 7637-2 Pulse 1 event to ensure that the output does not swing negative:

Equation 3. C O U T =   ( I L O A D +   I I S O _ A V G )   × 1   m s   Δ V O U T

where, ΔVOUT is the difference between VOUT at the start and end of the ISO 7637-2 Pulse 1 transient event.