Hi everyone,
We are using a BQ25050 charger in our product. It works great, but we are adding a testing step in our production where we want to measure the system power draw after assembly. The system consumes in the range of 100uA, so since the battery currents are at a minimum 95mA with 7% current measurement accuracy the system power consumption will drown in the battery charging current. What we are trying to do in order to solve that problem is get the BQ25050 to turn off the Qbat FET and regulate 4.2V on the OUT pin. According to table 2 in the datasheet of the BQ25050 you can send 1 pulse and it should terminate the charging. I am measuring the current on the USB port side and can see that there is a period about 30ms long after the force termination pulse has been sent where it seems to terminate the charging, but it then starts again. If I first send the Force on command (3 pulses) and then the force termination command nothing happens, so it would seem that the 30ms of no charge is indeed the force termination triggering.
This is the system state:
Battery voltage is around 3.9V
OUT is connected to the system.
TS is connected to a 47k NTC resistor
The ctrl pulses are high for 0.5ms.
CHG is pulled high through a MCU GPIO
IMON is connected through a 1k resistor to ground
What am I doing wrong ? Why does the charge cycle restart after around 30ms ?
