Hey,
i have got problems with the BQ20Z95 on our 3s3p battery pack. If i hold the SMBus lines low for 'bus low time' (5 seconds) while charging or discharging (current = 2A) the BQ20Z95 reports current as 23mA.
Our charger communicates with the BQ20z95 using SMBus every 15 seconds. The charger reads several parameters from BQ20Z95 like current, voltage and so on. After all data is acquired the charger holds the bus lines low for 15seconds until it starts communicating to BQ20Z95 again.
So the normal communication cycle is like that:
1. Bus lines low for 15s
2. Bus lines high
3. wait 5ms
4. get all data from BQ20z95
back to 1.
The problem is that the current is reported way lower than it realy is. It's not a calibration problem because if i wait longer, than BQ20z95 reports the right current. Longer wait times won't help me, because of the lowered average current due to false current measurement. Gas Gauging isn't working properly, too.
I found out that if i wait even longer than 15 seconds the BQ20Z95 eventually measures the right value again. Usually 20 seconds after the bus lines got low, BQ20Z95 measures a right current value.
With Bus Low Time i can alter the time which the bus lines need to be low for wrong current measurement to occur.
Any ideas how to get rid of the problem?
Jan