What is the rough efficiency of this IC at charge rates below 0.5A charging a 3.7v battery and operating off 5v input? The datasheet only provides efficiency documentation down to 0.5A charge rate.
The scenario: Our device uses an onboard BQ24170 to charge the internal 3.7v battery. A separate booster device has another similar 3.7v battery whose output is boosted to 5V, and then used as an auxiliary battery pack for the primary device.
The device charges while operating, so there is likely to be a concurrent 0.25A draw on the device battery while charging. The initial state would be both primary and secondary batteries will be fully charged.
I believe this leads to a state where the BQ24170 is simply replacing the 0.25A of current that the device is using over an extended period of time, drawing down the voltage of the auxiliary battery first (slowly), then switching over to running off the device's own internal battery.
Based on the general specs of 90%-ish efficiency, I'd expect the 2nd battery to increase the runtime to 80-90%, but we're seeing only seeing around 50% increase in runtime.
Could the BQ24170 be consuming enough current to create a loss of efficiency like this over time? We are using 3.7v 24Ah batteries, so charge and run time is generally measured in days.
Thanks for any input!
Chris
