Hello,
I like to ask for some help about to dimension the bq51050b circutry correctly: The design is like the input one of the "TIDA-00669" Reference Design with
an BQ51050B in use with a low size 160mAh battery of type RENATA ICP641620PA which has only a max. charge current of 180mA. Additionally the receiver
coils should be small and best of WUERTH type WE76038101303 with 19mm diameter or of type WE760308101220 with 17mm diameter.
The circuitry looks like this:
Observations:
I measured Urect, Ubat with a scope and Ibat with a Keithley multimeter. For the transmitter coil I used the standard WUERTH Qi transmitter pad of type T20.
- when placing coil 1 as in the circuitry in the center of the pad I see scope voltage pulses of Urect with 8..15V repeatedly every second and lasting
some tens of a second. LED1 or !CHG is off
- when placing this coil at the border of the transmitter pad as such that only about 40% of the area of the coil is within the transmitter coil Urect sets
correctly about 200..300mV above the Ubat~3.6V of the battery and LED1 is lighting, but the current measured through battery is not changing sign, but
only rising from -0.4µA to -4mA because of additionally sourcing the LED1. I would then like to see about +180mA
Questions:
1. Is the selection of the design and chip chosen correctly for the situation with this small battery RENATA ICP641620PA? Should it not principally working?
2. Within the BQ51050B datasheet nothing is said about size and dimensioning of "R1", the resistor between RECT and FOD? What is the rule?
3. What other dimensionings could be altered to use the coils also in the center of the transmitter pad?
Thanks in Advance Markus