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When using the DRV 8307, do you have recommendations for interface to MOSFETs for higher current loads?

Aaron Needles
Intellectual 615 points
Other Parts Discussed in Thread: DRV8307, DRV8307EVM
I am working on a motor controller design based on the DRV8307, and have the following questions:
1. The DRV8307 datasheet does not specify a parameter for dead-time during FET drive transitions. is this number available? We would like to know how much margin we have when considering FET on and off timing.
2. We are using TI's DRV8307EVM reference design and are modifying the drive section to support the BLDC motor indicated in the table below. There will also be a gearbox attached.
I am working out the details for interfacing International Rectifier IRFI1010NPbF power MOSFET for the inverter stage. We anticipate up to 10-20 amps for phase current. Are there particular recommendations for interfacing the DRV8307 to support this application? We have already worked out various details for adjusting sense resistor and bulk capacitance on the 24V supply bus, but we could use guidance on FET interfacing for the DRV8307 driver. Is selection of a sufficient gate resistor sufficient (for suppression of gate ringing and limited dV/dt), or should we consider other circuitry to keep the FETs within optimum operational limits?
 I appreciate hearing any thoughts on the subject.
Thanks,
       Aaron
Base motor, Bodine Electric model N3507
http://www.bodine-electric.com/Asp/ProductModel.asp?Context=15&Name=34B+Series+BLDC+Motor&Model=N3507
Speed (rpm)
2500
Rated Torque (oz-in)
101
Rated Voltage (volts)
24
Motor HP
0.25
Torque Constant (oz-in/A)
9
Voltage Constant (V/krpm)
6.7
Winding Resistance (ohms)
0.17
Winding Inductance (mH)
0.4
 
 

  • 0
    TI__Mastermind 20985 points

    Hi Aaron,

    We've measured a typical dead time of 345ns. This will vary some device-to-device, and it'll be shorter if the FET used takes longer to turn off due to a larger Qg, but at least that'll give you some idea.

    It looks like that IR FET could work. However, it is designed for 40A continuous and has a large Qg, so the switching time will be greater. If that turns out to be a problem, you might want to look at lower current FETs.

    As a starting point, I would first try using the default FETs on the DRV8307EVM, and they support 8A continuous and >20A peak. I would also decrease Rsense and increase the bulk cap, as you said. Use an external power supply with a current capability of at least half of 0.25V/Rsense.

    The only "circuitry" I recommend adding for the FETs are a 0ohm series resistors on each gate driver, and possibly a cap from sense to GND, and possibly a cap from VM to sense. Those are all shown in this reference design: http://www.ti.com/tool/tida-00196 Sometimes no-install caps are also placed between source and gate, and VM and source, but I don't think those are needed or necessarily useful in most cases.

    As for the layout, be sure to use wide traces on the high current paths. And place the bulk cap close to the FETs, with many vias to connect planes, and a minimal current loop distance.

    Best regards,
    RE