I am testing a board with the components : BQ7692003 and BQ78350DBT, I made a first version of it, with the boot switch linking VC1 to TS1 and it worked well, but for now I needed to change it and adopt a boot switch alternatives as shown in the "Application Report - SLUA769". I choose the scheme "Figure 5. Pack Boot Switch From REGSRC, I put here a screenshot of it, with the components values :
My schema is the following:
BQ_TS1 : is connected to the p.6 TS1 of the BQ76920.
RegSRC : is the input of the BQ76920, linked to its p.9 REGSRC and p.10 BAT.
Vdrive : is the output of the BQ76920, linked to its p.8 REGOUT.
Pack-_CHG : is the Source of my Charge MOSFET, so this is the Neg pin of the charging unit placed before the BMS unit.
GND1 : is the GND of the BMS unit, linked to the p.3 VSS of the BQ76920.
Normally I should use 5 x 18650 cells, but for the test I replaced them with a power supply, set at +19.0V (like if each battery had +3.8V). When I switch on the power supply, I can see on the Q408's p.2 (S) +19.4V and +17.0V on the Q408's p.1 (G), so my Vgs=17-19.4= -2.4V but I can't see any tension on the Q408's p.3 (D), the current should pass through the FET isn't it ?
I am a little bit confused with all the differents ground references on the scheme, I think it could be a source of error.
Can you help me with that please ?