LM5039: LM5039 Current Sense discussion

Hi Cheng,

In the datasheet of LM5039, the two methods can be employed in sensing the primary current. If using resistor to sense current, you need to care about the restart time and the value of the RES capacitor can be reduced to decrease the time before restart cycle is initiated. When using the resistor current sense method, an imbalance in the input capacitor voltages may develop when operating in peak cycle-by-cycle current limiting mode. If the imbalance persists for an extended period, excessive currents in the non-sensed MOSFET, and possible transformer saturation may result. This condition is inherent to the half-bridge topology operated with peak cycle-by-cycle current limiting and is compounded by only sensing in one leg of the half-bridge circuit. It is recommended to activate average current limit circuitry in such a configuration. However, since only alternative cycles source current into the ACL capacitor, ACL capacitor needs to be halved. This could still lead to a slight imbalance depending upon the input/output voltage levels and the impedance mismatch between the two phases of the half-bridge due to the additional CS resistor in the bottom half.

So I think you can recommend customer to use CT to sense current of high side and low side MOS to avoid the possible imbalanced issue.

BR

Jerry Xu