REV BLDC MC V1.0 part 2

It has been awhile since my last blog, and I decided to finish this series by the break. So let's do it.

In this blog I will discuss the PCB design of the controller, from schmatic to layout.

The primary component of this motor controller is a DRV8301 MOSFET gate driver. This chip is the connection between logic signal to power stage; what it does is that it takes in the control signal to the microcontroller (3.3/5v logic), and amplify this signal to drive the mosfets. The reason such a driver is required is because power mosfets has gate capacitance which can sink quite a bit of current for some time, plus it is usually 12v; a microcontroller cannot provide such signal power, especially at high frequency.

Besides the gate driving function, DRV8301 also include hardware/software support such as voltage/current protection, current shunt amplifier, mosfet hand shake,SPI communication, overtemperature protection. It also includes a 1.5A buch converter which can be used to power the MCU. (1.5A on such a small chip is quite beefy)

Here is the schematic and design:

Main Driver Circuit

Mosfet Bridge Circuit

The schematic is quite simple; TI (Texas Instruments) has planty of reference designs for this chip and its cousins. Here is a good example. 

Another source of support that must be mentioned is Duke Electric Vehicle. It is with their inspiration that we decided to use DRV8301 instead of other controllers, and it turns out that this choice is good for long term development.

 The second part, the tricker one, is the layout. 

top side

bottom side

The software used is Diptrace, which gave me a really smooth exprience while doing this design. DRV8301 is specified as a bridge between MCU and MOSFET bridges, so it also has a user friendly pinout: logic input pins on left side, power control pins on the other. As you can see from the top side layout, the traces are kept relatively clustered around IC; there are no long traces that cut across the ground fill. DRV8301 is on the top left corner, and it nicely spreads its traces from right to the power stage and its left pins going down to the MCU (from via throgh the bottom traces). 

On the power stage, it's the copper pours that does all the work. Copper pours are thick and large so that can handle large currents and more heat. Bulk capacitors are kept near the power inputs so the decoupling will be quick and effective. 

Here is a 3D view of the design:

3D model

Some of the components are not shown because the components don't have 3D model; however, this model gives a good idea about how it will look like. 

Part 3 coming soon for those of you who wants to see this thing in real. : )