BQ24171 Over Discharge Protection

Adam,

The bq24171 doesn't have any direct way to prevent overly discharging the battery. If we look at the typical 2S application circuit (Datasheet page 4) the external FET Q3 will always connect the battery to the system when the adapter is not present regardless of battery voltage. 

To add protection to prevent overly discharging the battery you have a couple options i can come up with right away:

1. You can design your system with a UVLO that will shutdown the system at the minimum battery voltage you want to stop discharging. 
2. If you are using a battery pack (not raw cells), the internal pack protection and gauge will often offer protection that will disconnect the pack under a certain minimum volts/cell.  (Work with your battery pack supplier to determine what protection they are providing)
3. You can add some external circuitry to disconnect the battery pack from the system below a minimum voltage. In the above typical 2S application circuit, since Q3 body diode will always allow the system load to draw current from the battery controlling that FET alone won't be sufficient.  We don't have a reference design for you to follow, but you could add an additional FET in the opposite direction of Q3 so the body diode blocks battery current and have it controlled by a comparator based on the battery voltage. 

Please let me know if this answers your question, or if you need any additional support. 

Thanks,

Rachel