I am including the BQ25040DQCT part in a design. The design takes 5V power from a wallwart, connects to the BQ25040DQCT to charge a .37V 18650 format Li-ion battery, and then goes through a DC-DC converter to produce a 3.3V source to be used by the rest of the design electronics (see picture below).
So normally, with a battery installed, the battery is always being charged and even if the battery is not yet charged, the BQ25040 supplies enough current (at 5V or 4.2V) through the BAT pin to power the DC-DC converter.
Two questions...
- I've read the datasheet a few times but can't figure out what LDO is for or how it should be used. Can anyone please explain?
- The datasheet figures 1 and 2 (shown below) says that when using 'With Battery Always Installed), to ensure there is at least 1uF capacitance on the BAT line to GND. But when using for 'Production Test Mode' (not sure what that even is), that >40uF of capacitance is needed on the BAT line to GND.
In my application, the device should never be operated without a battery. But besides the cost of the larger capacitor, is there any reason to not just include a greater than 40uF capacitor?