If CQ40 laptop has a good B+ main supply which necessary for the system to turn on always supplies(3VL and 5VL). Always supply is to maintain the system in a ready state before pressing the power button.TPS51125 is used in CQ40 for standby supply regulation.
Note: Check B+ and Charging supply Articles for Details
LDO or Standby section
In Compaq CQ40 B+(18.5v) supply apply to pin16 of tps51125 It receive power supply for ic’s LDO (3.3v and 5v)
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