MP8795H Simulation and Design Query

DC-DC Power Converters
1

Hi Team,
We are using the IC MP8795H for generating power rails 3.3V@12A and 3.45V@13A. We have few queries regarding the calculation and simulation for MP8795H using MPSmart. Can you please help us with the same. Below are the queries from our end.

  1. We are trying to generate 3.3V, 12A at a switching frequency of 800kHz and the calculated Cout value is obtained at 56.3uF. But while simulating at the same value, the simulation fails. We require a quantity of 7 numbers of 47uF for the simulation to pass and to be stable. We tried calculating the same for the reference board design (EV8795H-LE-00A) provided on the website and we did find such huge difference from the calculated value and values used for simulation. This difference is prior to derating and post derating we need nearly 10-15 quantities of 47uF. I am attaching our calculation sheet below. Can you please check and let us know why there is such a huge difference in the Cout value?

  2. The 3.45V rail is fed to 6 separate loads each of which requires 200uF bulk capacitance. An indication of the layout is given below in terms of separation between the Cout of the SMPS and the position of the individual bulk capacitances. We will implement a 1oz copper layer for distribution of the voltage rail. Is this layout likely to impact to the stability of the MP8795H? Will some of the additional bulk capacitance contribute to Cout or is the separation between the supply and the bulk sufficient. Sufficient. If you have any thoughts on a better layout approach please let us know.

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  1. Is there any means to figure out the power dissipated at the IC excluding the Inductor power losses, or do we need to calculate this loss ourselves (i.e. it is not determinable from the simulator). This would be very helpful for us to calculate the power dissipation of the buck convertor itself and the subsequent temperature rise of the device.

  2. We have been trying to calculate the efficiency using MPSmart simulation tool for MP8795H, but we keep getting the efficiency to be 99% irrespective of the change in the DSR and ESR changes in the L and Cout values. Can you please help us understand how the efficiency calculator in the MPSmart simulation tool operates, so that we can figure out our efficiency.

Thanks You.

2

Hello rithu.hari,

Welcome to the MPS Technical Forum.
I see that you are registered with a company email, so our FAE team would like to handle your case off the forum through MPS Now. Please submit a ticket request form with the link provided. This will be the best way to answer your questions and assist with your MP8795H application.

Meanwhile, I will work on posting answers here on the forum in a couple days.