Part Number:BQ76930
Dear all,
we are a design and manufacturing factory of electronic devices.
We have developed a board, which includes a BMS for a 36V Li-Ion battery (Iout max 15A), plus a microController.
The BMS is composed by the Texas Instrument BQ78350-R1, BQ76930 and BQ771807. The microController manages the board’s in/out algorithm and it can also read/write the Gas-Gauge by the SMBus.
A pushbutton is connected to the board (microController + AFE) and it acts to switch on/off the BMS output (36V – the Gas Gauge runs ; or no voltage output – the Gas-Gauge shutdown).
Today some samples of boards are ready, but we discovered the following issue.
When we connect a resistive load on the BMS output terminals, everything works correctly; but if the load is also capacitive (220 uF 63V connected to the BMS output terminals), the BMS does not switch on the 36V output (the CHG and DSG mosfets do not activate in a stable manner).
With the capacitive load, every 2-3 seconds the BMS continuously tries to power on the output and it switches on only after 1 … 10 minutes.
The output schematic stage is like the one of the BQ76930 datasheet “10.3.1.3 Control Subsystem - Figure 8. CHG and DSG FET Circuit”.
1) Can this power stage switch on a resistive and capacitive load? (220 uF)
Due to the capacitive load, at the power on surely there will be a pulse current, but monitoring the BMS with BQstudio, at power on we do not see any current protection fault. Only the AFE_OVRD “blink”.
Inspecting the Alert pin with an oscilloscope, it goes to high for some hundreds of milliseconds (the Alert pin is grounded by a 500 Kohm resistor).
2) What can we check further in order to understand the reasons of this issue?
Any help would be very appreciated. Thank you very much.
Best, Devis