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Hello,
I am working on a BQ78350 design using a BQ76930 analog front end. I am having trouble during some high short-circuit pulses.
The pulses are around 260A for 400us.
The problem is with the power input to the BQ76930. I have a separate connection to the cell for the input, but during a big pulse, the voltage will dip enough to shut the BMS down.
I tried putting a diode into the input rail, and this solution worked for the pulses; however it created a different potential between the VC10 input and bat input. This caused unstable cell readings.
My question is, what purpose does the diode between VC10 and BAT serve and could i remove it?
I have attached a [picture of this schematic section for reference.
Hi Alex,
The purpose of this diode is described in Section 3 of this application report: https://www.ti.com/lit/pdf/slua749
It should not cause unstable cell readings, so there could be a different issue.
Best regards,
Matt
My apologies for the confusion.
I caused the unstable voltage readings by placing a diode into the BAT (Pin 15) power rail to keep a reverse current situation from happening during large short-circuit pulses. I would like to keep this modification to the recommended schematic if possible.
This modification caused a difference of 0.5V potential between pin 15 and 16 which caused unstable readings.
I am not using the chipset based balancing, so my question is, can i removed the diode (D8 in my schematic) between pin 15 and 16 to disconnect the pins from each other without causing issues during normal operations?
Hi Alex,
The diode between pin 15 and pin 16 is recommended and should not cause unstable readings, so I am not sure what might be causing this.
Hello Matt,
After some more experimenting, removing the extra diode (D15) that i put in place and relocating that capacitor to the other side of R78; everything is running stable.
I believe I caused the unstable readings by adding D15 to the input of the AFE which was not in the recommended application schematic
Hi Alex,
I am glad to hear the issue appears to be resolved.
Best regards,
Matt