LM5122: negative input to positive output

Hello,

It is possible to do a negative to positive converter using the LM5122. The difference between the input and the output needs to be below the ABS max of the SW pin which is 100V, which it is for this application. There is no dedicated calculator for this configuration the but PMP20371 is a good starting point for this design. Due to the large output current requirements (12V-53A) this application will need to have multiple phases. Please let me know if you have any questions.

Thanks,

Garrett 

Hi Garrett,

Why do we need multi phase?

I want to know where is the limitation of controller like LM5122, because from my understanding if controller only provide driving signal, there should not be rating limitation if the MOSFET have been chose big enough.

Is that comes from the driving current controller can supply?

or there are other reason?

Thanks for your help.

Hello,

Multi-phase means using multiple controllers in parallel to split the power evenly between stages. For example, in a 1kW application if two phases are used then each phase will only see 500W of power. This helps to reduce the power train component physical size and also makes thermal management easier.

In a controller the reason that multiple phases are needed is usually related to the maximum gate drive current. Gate driver current is related to the rise time of VGS on the MOSFET, which is related to the switching losses. The slower the rise time the higher the switching losses. The internal gate drivers can only drive so many parallel MOSFETs and keep the switching losses to a minimum. In high power applications sometimes multiple MOSFETs are needed on both the low-side and high-side.

If you have any more questions, please contact me directly.

Thanks,

Garrett