SLUAAT7 January   2024 BQ25672 , BQ25790 , BQ25792 , BQ25798

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2IRMS Discharge Current
  6. 3External Battery FET
  7. 4Charger With PG and or Host GPIO
  8. 5Buck-only Charger
  9. 6Boosting Charger
  10. 7Summary
  11. 8References

6 Boosting Charger

If the charger only boosts or boosts and bucks, an additional IC is needed to drive the external PFET’s gate low when input power is removed. A comparator determines when the input voltage has been removed. The comparator needs a reference for the negative input to compare to the charger’s input voltage. The reference does not have to be extremely accurate, must be present when the charger's input voltage is not present and does not need to provide any significant current. QON, powered by the higher of the input or battery voltage, can be used as this reference as long as the charger’s minimum operating input voltage is above the QON maximum voltage [V(QON)MAX], of 3.3V. As soon as the input voltage drops below V(QON), the comparator turns on the PFET. TLV1861 is a comparator with up to 40V input (up to a 9S battery pack), quiescent current of 440nA typical and open drain output.

GUID-20231211-SS0I-XTZ0-TMDM-5ZG8V7JGSNB2-low.svg Figure 6-1 Implementation for Boosting Charger

The Zener diode clamp, D1, from the PFET’s source to gate is only necessary if the battery voltage is higher than the PFET’s max VGS.