Using MP9929 with high voltage bus

DC-DC Power Converters
1

Hello,
We are thinking about using MP9929 for our 500-300 Vin , 270 Vout buck converter with 5kW power. We will feed the controller with an isolated 12V supply and use external gate driver to drive the mosfets while grounding SW and Bootstrap pins to not exceed absolute maximum rated voltages of these pins. Is this a appropriate solution or do you have any other suggestion for our system?

Thank you

2

Hi Bektasb21,

Welcome to the MPS Forum.

I do not believe this will work for your application. The BST pin is used as a floating supply for the internal high side FET’s, grounding will result in the internal HS FET not turning on and could result in irregular controller behavior.

You can simulate the behavior of your system with MPS Parts using MPSmart in the meantime. To get the SIMPLIS model for the MP9929, please submit a ticket to MPSNow.

Could you clarify, are you stepping down from 300-500Vdc to 12Vdc to be used as the input for the controller? Could you provide a diagram of what you are trying to achieve? What application is this for? A block diagram would be beneficial.

3

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Hello
As you said connecting the BST pin to GND is not a good idea but we think that left it floating may work. What do you think?

Also I added the block diagram as requested and open for recommendations

4

Hello any update on the topic?

5

Hi bektasb,

Apologies for the delay, I was searching for a solution to your questions and applications. Thanks for providing the block diagram for your application.

Running a simulation, leaving BST may be OK. I will add that this is outside the typical application, therefore although a simulation may give some indication on steady state operation, a bench test would be needed to verify.

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Unfortunately, the MP9929 is a 100V rated part, I attempted to simulate with an input > 100V which resulted in an error. Benchtop tests would most likely damage the IC and result in a non-functioning part.

For a higher input voltage you can use the MPQ4590-AEC1 which can go up to 640V as a non-isolated converter. Though it is limited by its load current (400 mA).

For this application, MPS does not carry a part capable of the output power you are looking for. I would suggest either using a discrete solution (discrete Diode, MOSFET, and Inductor) or an isolated solution.

6

fine idea, could work, but… what is going to get up is the current sense input, which is only rated to 28V.
So maybe you could sense down at ground level or use a current sense transformer