Hi everyone, there is an information how to arrange the over current protection for MP5048. Bu i could not find any information about how to calculate the RCLREF resistor value and the Rcs resistor value. Also what is the VCLREF_NORM value of the MP5048?
I want to set the over current protection arund 6A and I need the resistor vales that i mentioned above.
Wow what a terrible and confusing data sheet. Just some weirdo here, what I see is the current sense outputs 25uA/A of fet current so 6A would be squirting 150uA out the CS pin. That will get compared to the voltage on the CLRef pin that has 26uA squirting out ( after the SS period has run)
The other nugget is there is mention of a CLRef clamp or 2V ( abouts !) so lets say we want the 26uA to avoid that. If we set CLref with 26uA to 1.5V then the CLref resistor will be 57.7k
If we want 6A in the Fet which gives 150uA on the CS pin to equal 1.5V then that resistor needs to be 10k
Get an eval board if you can and good luck
Hello @huseyin.yildirim ,
Apologies for the confusion regarding setting the OCP.
We have this equation for setting the current limit on page 17:
GCS is stated to typically be 25uA/A.
VCLREF_NOM is stated to be the CLREF pin voltage during “normal operation”, meaning after soft start. There is the option to use a controller, like the MP5920, that regulates the current limit by regulating the voltage sent to VCLREF pin on the MP5048.
If a controller does not send a voltage to VCLREF, MP5048 can generate a voltage on VCLREF pin using the stated 26uA (8uA during SS, 26uA during normal operation) that VCLREF can provide. The pin can handle up to 6.5V as stated in the absolute maximum ratings, and as jshannon stated, the DS states there is a clamp of about 2V on the pin. Pick any voltage below 6.5V, lets say you don’t want the IC to clamp the voltage, so you pick 1.5V like jshannon did. R = V/I, so R_CLREF should be 1.5V/26uA = ~57.7k. Our evaluation board uses 62k, so we create a voltage of about 1.6V.
Given you want Current Limit of 6A and VCREF_NOM to be 1.5V, as chosen in this example, and since we know Gcs is typically 25uA/A, we can use the first equation to calculate Rcs to be about 10k.
Though this information is all in the datasheet, I will ask to make the calculation of VLREF_NORM more clear so that the calculation of Rcs is clear.
Regards,
Jonathan Hidalgo