Hi all,
I'm hoping you can help me with some erratic behaviour I'm seeing with the BQ24250. I have a battery powered device that has a ~450mA current draw. It is powered by a LiPo battery, 3.7V Nominal, 2.5Ah. There is an NTC placed at R15 due to the battery not having its own NTC. The net to supply the system is VCharger_Out.
The device can recognise when it is connected to two types of charging sources, e.g. a PC or a benchtop PSU (500mA max) or a wall adapter (2A) with U26, 27 and 28.
The BQ24250 charger is configured to charge a LiPo battery at 1A with 249Ohm R21. I am monitoring current going directly into the battery (J3) with a Keysight 34460A DMM.
When I connect the USB charger, the system is powered through the BQ and no current flows in or out of the battery, regardless of it being a Dedicated Charging Port (DCP) or a Standard Downstream Port (SDP). My guess is the BQ24250 defaults to a state where it thinks the batter is charged and it supplies the system. This can also be verified by two pulls ups (R45 & R46) I have connected to BAT_STATUS and BAT_CHG of the BQ. In this non charging state, the two status pins are open (or hi-z).
If I connect the USB and wait for a couple of minutes, approx. 7 minutes, charging commences. It begins charging at exactly 500mA. After 10 minutes of charging at 500mA, the charge rate increases slightly to 580-600mA and then begins slowly dropping. I am currently profiling how the remaining charging performs so I should have follow up info on termination currents which are defined in the screenshots below.
My main concern is why the delay to begin charging? Why am I not charging at 1A given that the BQ can supply 2A when running the system and charging the battery?
Hoping the community has an answer for this or to get me started on where to look. If anything needs further clarification please let me know.
