[FAQ] LM5066I: How to select Power MOSFET in Hot-Swap design ?

A hot-swap circuit uses a power MOSFET as a series-limiting device and controls start-up inrush and fault currents.  During transient and fault events, the MOSFET dissipates power greater than steady-state and can exceed the thermal limits of the MOSFET, so designers must ensure the MOSFET is operated within its Safe Operating Area (SOA).  There are many good resources available to help designers choose a suitable MOSET to meet the power dissipation requirements under all of the events. 

• Application note “Robust Hot Swap Design” covers the detailed design procedures involved in MOSFET selection. 
• Texas Instruments also offers detailed Excel-based calculators for Hot Swap applications using power limiting that follow the approach outlined in the application note. Each of the hot-swap controller has separate excel-based calculator to help in the design.

An example design calculator for LM5066i is LM5066I Design Calculator.  However, the designer needs to pick a MOSFET and enter SOA parameters in the design calculator to verify whether the selected FET meets the design or not. Usually, the designer has to tune the requirements or select a stronger MOSFET involving serval design iterations.

To simply the process, Texas Instruments has released design calculators with FET recommendation for some of the popular controllers. Tool details are given below to explore further…

LM5066I Design Calculator With FET Recommendation

LM5069 Design Calculator With FET Recommendation

LM25066 Design Calculator With FET Recommendation

Additional resources:

https://e2e.ti.com/blogs_/b/powerhouse/posts/how-to-select-a-mosfet-hot-swap 

Handling System Transients in Hot Swap Applications