**Part Number:**TIDA-00688

**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 9.2.12.5 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 example:

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..**