Hello,
I am designing a battery charging circuit using the BQ25756 integrated circuit and plan to power the system with a solar panel operating in MPPT mode. In TI's reference design (as shown in the schematic I attached), there is a 2.4 ohm series resistor and a 100 µF capacitor between the connector and the BQ25756 on the input side. The input range is also specified as 12–48 V.
Below are three questions I have:
1) What exactly is the purpose of the 2.4 ohm series resistor and 100 µF capacitor used in the reference design?
Are they used solely for “inrush current limiting,” or do they also serve other functions such as input filtering, EMI reduction, surge suppression, or VAC/ACN measurement stability?
2) I placed this RC structure at a different point in my design than in the reference. The construction is as follows:
Connector → Common-Mode Filter + X/Y Capacitors → MOSFET reverse voltage protection → Load switch → 2.4 ohm + 100 µF → BQ25756 (VAC/ACN/ACP).
So, compared to the reference, the 2.4 ohm + 100 µF block comes after the entire EMI filter and protection block. Is this placement acceptable from TI's perspective? Does the placement of this RC network before or after have a critical effect on the BQ25756's input measurements, stability, or protection behavior?
3)I did not change the 2.4 ohm and 100 µF values in the reference design because my input range is currently similar. However, I want to make the input operating range 5 V–70 V in the future.
In this case, what should I base my selection of the 2.4 ohm and 100 µF values on?
Do you have a recommended calculation method/equation for this RC block?
Thank you.
