Q3 is a low-cost PCH FET and is used to keep CHG awayfrom any voltages below VSS. When CHG is not beingpulled high, PACK± being pulled below VSS will not beseen by CHG as Q2 does not turn on. Q3 also allows R2 tokeep Q1 OFF, since all voltages below this FET can Q3 "follow" PACK± as it goes below VSS.