MPLAB Mindi: a simulation of MCP16331 click board

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Simulation of the MCP16331 click

The best way to show you the capabilities of MPLAB Mindi is to simulate some circuit. And the best candidate I had for simulation is an MCP16331 click board from MikroElektronika, a buck-boost converter built around the highly integrated, high-efficiency, fixed frequency, step-down DC-DC converter Non-Inverting Buck-Boost Application MCP16331, in a topology similar to the one indicated in figure 7-2, on page 31 of the MCP6331 datasheet.

MCP16331 click board

MCP16331 click board

I will start with the schematic of the click board, keeping only the area highlighted in red:

Schematic of MCP16331 click board

Schematic of MCP16331 click board

The schematic has to be created in MPLAB Mindi. When starting Mindi, you have the option to start either a new SIMetris schematic or a SIMPLIS schematic. The choice is easy to make: the MCP16331 IC is available only in SIMPLIS. As such, we start a new SIMPLIS schematic; we go to Microchip Library → Power Management → Switching regulators, and we place one MCP16331IC. The closest thing to the BZT52C2V7 Zenner diode is a 21N5224V/PS, and instead of the AO3418 MOSFET, I used one IRF530, which exceeds the specifications of the original MOSFET. A 66Ohm resistor being used as a load.

Three waveform generators are used to simulate the power supply, the output of the MCP4921 DAC and to drive the EN line.

The schematic in MPLAB Mindi is:

Schematic of MCP16331 click in MPLAB Mindi

Schematic of the MCP16331 click in MPLAB Mindi

  • The whole project can be downloaded by following this link.

Now everything is set up, let’s do some transient analysis.

Power-up sequence

On the product page of MCP16331 we find the following power-up sequence:

  1. Disable the MCP16331 by setting the mikroBUS™ pin RST (EN) low (GND)
  2. Set the desired output voltage via SPI (see the software section below)
  3. Enable the MCP16331 by setting the mikroBUS™ pin RST (EN) high (5V)

Why this? What happens if we do otherwise?

Let’s simulate the power-up sequence, with EN being driven before DAC output is set:

Boost mode, EN before VDAC

Boost mode, EN before VDAC

Buck mode, EN before VDAC

Buck mode, EN before VDAC

We notice that, both in buck and boost modes, the output voltage grows rises to over 12V if VDAC = 0 and EN is active.

Let’s repeat the simulation, this time applying EN before VDAC is set:

Boost mode, VDAC before EN

Boost mode, VDAC before EN

Buck mode, VDAC before EN

Buck mode, VDAC before EN

Quite a different thing, isn’t it?

The relation between Vout and VDAC

Once again, a simple simulation. This time I’ve set VDAC as a triangle signal.

Vout vs VDAC, Buck mode

Vout vs. VDAC, Buck mode

Once again, a nice graphic. We can see here that the output voltage is inversely proportional to VDAC.

Current flow through the inductor

Current through L1, buck mode, Rload = 10R

Current through L1, buck mode, Rload = 10R

It looks I’m asking a bit too much from the click board, the current is quite high… I will change the load to 200 Ohms.

Current through L1, buck mode, Rload = 200R

Current through L1, buck mode, Rload = 200R

This is extremely difficult to do in real life, as it requires a current probe, an expensive piece of equipment. In the simulation, you get this easy by just placing an inline current probe.

A few final words

MPLAB Mindi is very easy to use. If you have basic knowledge of how a simulation program works, you will be ready to use Mindi in just a few hours.

Even a simple thing as a click board can become complicated when you take a closer look. This time MPLAB Mindi has allowed me to an analysis that would prove otherwise difficult, or just impossible due to lack of dedicated test equipment.

Many click boards can be simulated in MPLAB Mindi, as they are built with Microchip components that you can also find in Mindi. By simulating those click boards in MPLAB Mindi, you can get a better understanding of how those click boards work.

 

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