Driving high current PWMs out of DRV8301

Hi Aleksandar,

The DRV8301 works in combination with external MOSFETs to drive higher currents.

You cannot connect a MCU directly to most power MOSFETs. You need some sort of interface, called a gate-driver or pre-driver.

It takes logic level inputs (MCU PWM signals) and translates them to the proper signals to drive N-type Power MOSFETs.

This video explains the difference between an integrated driver and a pre-driver/gate-driver.

https://www.youtube.com/watch?v=A3U6uiipWLM

Ok, so if I understand correctly, that means the MOSFETS are the switches that will take the high current coming in from the drain and fan them out to the source, then subsequently the motor?

If I look at the CSD18533Q5A N-FETS, it says they have a continuous drain current of 17 A. So, if I connect the source of these FETS to each phase of my motor, I should be able to get this high current output I'm looking for, provided I have a high enough PVDD voltage at the drain?

-Aleksandar Zivkovic

Correct, for a pre-driver/gate-driver, the power MOSFET switches are external. They will be handling the motor current.

Yes and no. The current continous current will depend on thermal limitations. The 17A is assuming ideal heat dissapation. Most real PCBs will not be able to achieve this without cooling, heatsinking, etc.

You will see on the BOOSTXL-DRV8301 that the MOSFETs we use are rated for much more current, yet the design can only drive about 10A before thermal limitations kick in.

Ok thanks for clarifying that Nick!

Now, looking at the schematic of the BOOSTXL-DRV8301, I'm also assuming that there's a cap at the drain of each nFET to stabilize the PVDD voltage supply, in case of any sudden fluctuations?

Also, which supply voltage PVVD value would you recommend to get this ~10 A thermally limited current? The  I-V curves for the MOSFET data sheet seemed to indicate a 30 V Vds (From Figure 5 page 4) to get that ~18 A non-thermally resistant Ids, but I wasn't sure if that was necessary or not.

Thanks once more for all your help, I really appreciate it!

-Aleksandar Zivkovic

Yes, bulk capacitance is used for when the MOSFETs are switching on and off or when there is a sudden increase in current to or from the motor. They stablize the voltage against these current transients.

PVDD will not greatly effect the thermal dissapation of the MOSFET. Your PVDD is set to be whatever the output of your battery is, so I am not sure you have much flexibility here.

It is more reliant on heatsinking and Rds(on). Whenever you drive current through a transistor there are loses due to the Rds(on) of the transistor. These loses are translated to heat which was must be moved to the ambient air, into the PCB, or other places.

I am unsure which figure you are looking at. Figure 5 is Qg vs Vgs.

http://www.ti.com/lit/ds/symlink/csd18533q5a.pdf

I am looking at this pdf.

Sorry I phrased that question poorly.

What I meant to ask was would my Id still be 18 Amps (then reduced to ~10 through thermal dissipation) if I used a 6V PVDD or a 60 V supply voltage (assuming I still meet the requirement Vds > (Vgs - Vt) to be in the saturation region).

Hi Alexsander,

We are actually operating in the linear region here. The MOSFET will pass through saturation when it switches on.

Rds(on) is mainly a factor of Vgs and temperature. Our gate drivers utilize a Vgs of 10V.

Ok right, I forgot the Vgs value is so high.

So, since Vs will be between 6 and 8 volts, do you still think we will be able to get this ~10A output?

I think this is doable. You will need to ensure proper copper heatsinking on the PCB.

If you look at the BOOSTXL-DRV8301 layout you will see large copper regions under/around the power MOSFETs to allow for heat dissapation