SLYT803B october   2020  – october 2020 BQ24610 , BQ25713 , BQ25790 , LM66100 , LM74700-Q1

 

  1.   1
  2. 1 Introduction
  3. 2 Understanding Battery Packs
  4. 3 Stackability Requirements for Battery Packs
  5. 4 A Multibattery Management System Design
  6. 5 Battery Charging
  7. 6 Battery Gauging and Protection
  8. 7 DC-to-DC Converter or Controller Stage (Boost or Buck-boost Stage)
  9. 8 ORing Control
  10. 9 Load Sharing
  11. 10Conclusion
  12. 11References
  13. 12Related Web Sites

8 ORing Control

An ORing function is required when multiple power paths must be connected together to form a single power source to a device. Traditionally, it is possible to perform ORing control using discrete diodes, but a major drawback of diodes is their high forward voltage drop, which causes high power dissipation and reduces the operating time of the battery. Replacing discrete diodes with an integrated ideal diode (like the LM73100 shown in Figure 4a) can help reduce the forward voltage drop. With the voltage of the battery decreasing throughout its lifetime, because the discrete diode will reach its minimum voltage threshold first, the forward voltage drop of the discrete diode disables the system faster than the integrated ideal diode.

Another benefit of using an integrated ideal diode is that it has a lower reverse leakage current than a discrete diode. When the main power supply is active, reverse leakage current flowing into the backup battery can reduce its lifetime by deteriorating its capacity. On the other hand, when the backup battery is powering the system, reverse leakage current flowing into the main power-supply path can result in wasteful current consumption. Minimizing the reverse leakage current helps extend the life of the battery.

Replacing the ORing diode with low RDS(on) FETs, driven by an ORing FET controller like the LM74700 in Figure 4b, can help further improve overall battery life and system performance.