SLUAAH5 November   2022 BQ25171-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1 Introduction
  4. 2 Li-Ion Overview
  5. 3 Li-Ion Applications
  6. 4 LiFePO4 Overview
  7. 5 LiFePO4 Applications
  8. 6 NiMH Overview
  9. 7 NiMH Applications
  10. 8 Super Capacitors
  11. 9 Super Capacitor Applications
  12. 10Summary
  13. 11References

8 Super Capacitors

Super Capacitors are relatively new options for power storage. Capacity of the devices have increased and ESR has decreased making them competitive with the other battery chemistries in some applications.

Super Capacitors are long life without wear-out factors and can be discharged to 0 V without degradation. Operation over a wide temp range is possible. Charging is flexible, can fast charge with high current or trickle charge, only voltage regulation is required.

Typical capacitor max voltage is 2.7 V and series capacitors can be required for higher voltage with possible cell balancing.

Energy storage vs. volume is low compared to other chemistries. Voltage on capacitor changes sharply with SoC, steep discharge curve. This requires a converter to provide stable output voltage as charge changes. No shipping restrictions for Super capacitors.



Figure 8-1 Super Capacitor Charge Profile

The typical constant current charge profile increases capacitor voltage at a linear rate followed by a voltage regulation phase, see Figure 8-1.

Note the current reduction due to thermal regulation of the BQ25173. This is a protection feature when power dissipation on device is high, see data sheet for more information on this feature.