Other Parts Discussed in Thread: CC2541
Hi,
We have been using LM3478 in our application to charge batteries. We also have a BT system on chip CC2541 in our product.
We are trying to achieve two things:
1. Instead of having a fixed limiting current, we are trying to have two limit current levels. We have a fixed 90 mOhm sense resistor (Rsense1 in the schematic below) and in parallel have a MOSFET (with 25 mOhm ON resistance, Q2 in schematic below). In most cases (95% of the time) we are limiting the current normally limited by the fixed 90 mOhm sense resistor.
In some cases we want to increase the current limit by switching the MOSFET ON (and thereby reducing the resistance as it is in parallel to 90 mOhm sense resistor). The effective resistance would be around 20 mOhm. We are not too keen on the accuracy of the limiting current (as the MOSFET ON resistance would not be accurate and will increase with temperature) in this case as long as it is less than 3.5 A. The SOC CC2541 will decide switching of this MOSFET based on certain conditions.
2. We also want CC2541 to sense the output current of the circuit.
Our questions are as follows:
For 1 above, will our approach work? Is there any issue in this approach?
For 2, can we use the voltage that also goes to pin 1 (Isen) of LM3478 to sense the current? Our understanding is that the voltage at Isen decides the current flowing thru the circuit. CC2541 will also sense this voltage.
Thanks in advance for your time and help.
Vijay
