Tool/software:
Hi,
I have designed a circuit using BQ25820 but with some variations from the datasheet and EVM schematic. I hope I can get some clarity on whether this can be done.
Some basic design parameters:
- Vin: 6V to 50V
- Vout: battery only
- Battery: 3.6V LiFePo4 battery
- Charge rate: 1.5A max
- Discharge rate: 8A max
- Switching frequency: 250KHz
Questions
- ACUV and ACOV
- I have used two separate resistive networks to control the AC input range, as I wanted to set them from 6V to 50V. The datasheet and EVM had them connected in a triple resistor network, so I'm unsure if there's some consideration that I might have missed here.
- I have used two separate resistive networks to control the AC input range, as I wanted to set them from 6V to 50V. The datasheet and EVM had them connected in a triple resistor network, so I'm unsure if there's some consideration that I might have missed here.
- ACFET and BATFET
- I kept ACFET to control input to the buck converter, but I bypassed BATFET, so battery is always connected to my system load. Also to note that the ACFET is not connected to my system load.
- My question is whether this IC could face any issues when the AC input is active, and the system load draws its maximum current of 8A. I anticipate that the buck converter will also experience increased load since the battery voltage may dip under these conditions, causing the buck to remain active. Although the maximum current is expected to last only a minute or two, could this pose any potential problems?
- I kept ACFET to control input to the buck converter, but I bypassed BATFET, so battery is always connected to my system load. Also to note that the ACFET is not connected to my system load.
- Inductor rating
- My max Iripple_buck seems to be around 5A at Vac 50V and D = 0.5. Am I correct to size the inductor at Isat ~=12.5A, or would that be excessive?
- Input capacitors
- What is a good way to size the value here? The EVM had the input capacitors at 56uF; could I size it down?
- Battery capacitor
- What is the typical acceptable ripple voltage range if I am using the BATFET?
- Design checklist
- I just wanted to check if you have any kind of Excel spreadsheet for calculating the design parameters.
I hope my questions aren't too much to ask in a forum. Thank you.