I am using the LM5069MM-2 from Ti for a project. This project requires an over current protection limit. The LM5069 can do this and the data sheet shows how. But I don't understand the process Ti uses to determine the effective sense resistance.
Here is the problem: The application current limit must be 3.8A. To set this current limit a sense resistor, Rsns, is selected. The selection of Rsns is based on the minimum threshold voltage (48.5mV) the SENSE pin of the LM5069 reads before it initiates the over current protection and the desired current limit:
Rsns = 48.5mV / 3.8A = 12.76mΩ
But sense resistors only come in whole value increments 11mΩ, 12mΩ, 13mΩ... So what we can do is reduce the effective resistance of the next larger sized resistor i.e 13mΩ to get an effective resistance of 12.76mΩ.
Here is where the confusion begins to take place:
How are they determining the values of R1 and R2? What theory are they using? The way they are doing it does not make sense to me. They just find a ratio of R1/R2 based of the sense resistor value I need verses the one I have. Then they apply a voltage divider-like equation to get an effective resistance. Can someone please shine some light here?
Thank you for your time,