Tool/software:
I have a circuit built around the BQ25756E that is almost identical to the EVM board from TI. I have double checked, tripple checked, etc. etc. that I don't have a wiring mistake, but I can't seem to figure it out. While I can get the EVM board to work as I need, I can't get my circuit working and I'm getting this fault flag: "DRV_SUP pin voltage is out of valid range". Measuring the voltage at REGN/DRV_SUP which are tied together, I get about 214mV. Voltage fed in to VAC is just under 36VDC. I would expect the REGN/DRV_SUP to be around 5V, so it seems like something is dragging it down.
My question is this: What are the possible causes for the REGN/DRV_SUP to be too low so-as to generate the fault flag? Where does the DRV_SUP feed go internal to the IC and how does that feed to the high-side drive? Actually, related to this, the diodes that feed this +5V to the biasing capacitors is a bit of a mystery to me. I am not understanding the point of these two diodes in relation to the FET driving circuit. I realize we need a voltage higher than the incoming voltage to fire the high side FET gates, so it seems to be a part of a charge pump. Are the diodes there mostly for protective clamping purposes?
Are there possibly I2C registers that I may be inadvertently setting that results in a disabled REGN output?
One other symptom is that the output voltage very slowly climbs up to about 2.75vdc. Very slowly is probably do the large capacitance on the output with the (3) 56uF caps.
Any pointers in the right direction are very much so appreciated.
..Sean Solberg