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BQ27742-G1: Settings check for safety and initial gauge

Eric Steimle
Expert 2290 points
Part Number: BQ27742-G1
Other Parts Discussed in Thread: EV2400, GPCCHEM

I'm working on the correct safety and initial gauge parameters for my BQ27742.
So far I have read the datasheet, large sections of the User Guide as well as SLUA544 (which seems out of date now).

I have an EV2400 and a custom board with the BQ27742 on it (schematic was reviewed by TI). BM studio can talk to it just fine.

I'm using a TI BQ25890HR USB charger to charge my battery pack. The TI charger will trickle charge a cell up until 2.8V when it will turn on the full charge current (I will have to limit that based on my batteries). When it reaches 4.208V - 100mV it will begin to taper off the charge current until less than 256mA flows. Then it will turn off.

I'm using two Grepow LIPO batteries in parallel, 600mAh x 2 = 1200mAh. Discharge at least 4A, charge 0.5C.

Based on my reading I think I have to set the following values in the data flash.

Over Voltage Protection - 4390mV. The charger will shut off at 4208mV as primary protection.
Under Voltage Protection - 2800mV.
Charge Over Temp - 65C. Charger will stop at 60C.
Charging Voltage - 4208mV. Note the charger turns off at this same 4208mV - 100mV
Tapper Current - 256mA. Matching the chargers shutoff current
Tapper Voltage - 100mV. Matches chargers -100mV setting
Design Voltage - 3800mV.
Cycle Count threshold - 1080mAh (90% of capacity)
Design capacity - 1200mAh
Design energy - 4560mWh

I also think I have to set the following "protector settings"
OC Discharge -34mV or 6.8A
OC Charge - 6mV or 1.2A (must limit charger current in charger to 0.5C or 600mA)

Have I missed any important safety configurations?
Is this enough to get my gauge sort of working? My battery vendor wasn't in the chemistry list so I didn't know what to choose there. Maybe I have to follow an updated procedure to figure it out.

  • 0
    TI__Guru* 76230 points

    Hi Eric,

    Set the taper on the gauge to be higher than the taper of the charger. So a value like 286 would be good just to make sure the gauge see taper conditions before the charger cuts of charging otherwise the FC flag will not get set.

    also make sure the taper current is greater than the charge and disharge current threshold both of which should be greater than quit current. quit current should be less than or equal to c/20.

    Also, to identify your chem id, follow the instruction listed in our online tool gpcchem. you need to perform a learning cycle after identifying and programming  your chem id following the instructions in the attached document

    2870.LearningCycleOverview_.pdf

    thanks

    Onyx