Other Parts Discussed in Thread: BQ51003, BQ25120
Hello TI team,
We are facing quite strange issue with our new design based on BQ51003 wireless Qi receiver and BQ25120A charger.
Here is the schematic:
3527.BQ51003+BQ25120A schematics.pdf
Please note that the secondary coil "COIL1" Ls=47µF. As we don't have the LRC meter for L's measurement, I based my design on 30% increase so around 60µH.
Please also note that Cs (C13 + C17 + C21) has been modified to 41.7nF and Cd (C19 + C20) to 550pF based on Ls and L's, which are not shown on the schematics.
As read on an E2E post about the BQ51003, I also changed Ccomm1 and Ccomm2 to 10nF, which may not be necessary? (https://e2e.ti.com/support/power_management/battery_management/f/179/p/648409/2406394?tisearch=e2e-sitesearch&keymatch=bq51003%2010nf#2406394)
After our IC boot, BQ25120A registers are set as follows (from 00h to 0Bh):
00 00 00 9d ba 78 aa 00 68 12 80 c2
When putting our wireless transmitter over to the Rx coil, we do have 5V on the BQ51003 output and BQ25120A input, however the charge current measured is around 4mA and BQ25120A registers show the following values:
00 00 00 14 0a 78 aa 00 68 02 00 42
We checked that the I2C master did not modify these values, as you can also see on the following saleae capture (change happens between the two frames at ~1.8s and 5s in the recording).
So it seems that the BQ25120A changes its registers by itself to non-default values.
This happens no matter how many times we cycle the wireless power transmission.
However, when we reset the BQ25120A using a long press (10s) on the push button on MR while maintaining the wireless Tx over the Rx coil (with ~4mA charge current), the charge current switched to 110mA and the registers are as follows:
00 00 00 9c ba 78 aa 00 68 12 00 c2
This also happens no matter how many times we cycle the wireless power transmission. Once the battery is removed then plugged back in, we have the same behaviour as stated before (4mA charge current and registers mysteriously changed)
Here are some scope captures showing the following signals:
1-Yellow : BQ25120A PMID
2-Green : BQ25120A SYS
4-Purple : battery current measured with a current probe
Standard discharge, no charger attached:
~4mA charge (3.86mA + 198uA = 4.058mA):
110mA charge after reset while charger is attached:
As there is no interaction between BQ51003 and BQ25120A except the 5V respectively output and input voltage, I guess the issue is BQ25120A related.
Thanks,
Damien