Other Parts Discussed in Thread: BQ25100, BQ51003,
Hi everyone, I design a wearable device using the bq51003 wireless receiver and the bq25100 battery charger and I am advising the reference design TIDA-00688. I need your advice regarding the max output current I have to choose for the bq51003 and how to set it.
My wearable has a low current consumption (<5mA in full power mode) and I will use a battery with a capacity 80mAh. The manufacturer suggests using a standard charging method of 0.2C, that is 0.2 x 80mA = 16mA charging current and I have calculated the ISET and PRETERM resistors of bq25100 to meet this requirement.
Given that the bq25100 will draw just around 16-18mA, is means that the bq51003 must provide at least 20mA? I have to take into account and the load as well? For example if the load is 5mA then the total output current of the bq51003 must be at least 35mA?
Now in order to set the limit current
According to the bq51003 datasheet section 22.214.171.124 the default value for RFOD = 196 Ω (the same as the reference design) and the RLIM is calculated as:
RILIM = R1 + RFOD or RILIM = KIMAX / IMAX (see datasheet section 8.3.4)
This is a screenshot from the Reference Design TIDA-00688 section 5.1. The table shows the various resistor values for the corresponding output current IMAX right? As shown from the reference design the R1 = 1.3k corresponding to a maximum output current of 240mA. Using the formulas above I cannot verify the results in the table..
for IMAX = 0.24A , KIMAX = 262, RFOD = 196Ω
RILIM = KIMAX / IMAX = 262/0.24 = 1092 Ω
R1 = RILIM - RFOD = 1092 - 196 = 896 Ω (for IMAX = 0.24A)
My calculations do not match with the table.. please advice..