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BOOSTXL-DRV8320RS: Snubber

Genatco
Guru 54057 points
Part Number: BOOSTXL-DRV8320RS
Other Parts Discussed in Thread: CSD88599Q5DC

Why was there no snubber circuitry shown in schematic, added to BoosXL protecting NexFETS above DC supply >42v? It would seem a mandatory requirement for a large PM motor. Are there pads on the PCB to populate said snubbers?

6.3 Power Loss Curves

CSD88599Q5DC was designed to operate up to 10-cell Li-Ion battery voltage applications ranging from 30 V to 42 V, typical 36 V. For 11 and 12s, input voltages between 42 V to 54 V, RC snubbers are required for each switch-node U, V, and W. To reduce ringing, refer to the Electrical Performance section. In an effort to simplify the design process, Texas Instruments has provided measured power loss performance curves over a variety of typical conditions.

  • 0
    TI__Guru 61280 points

    Gl,

    Thanks for posting on the MD forum!

    This board was designed by the C2000 group so I cannot say exactly why snubbers weren't added. Speaking for the other EVMs of similar design made by our group, we felt for the voltage and power levels that these boards were supporting we could get by without the snubbers so we left them off. Of course you can add these in your schematic or blue wire them to the EVM if needed.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Guru 54057 points

    Hi Adam,

    Can you forward this to that team to add pads on the next version since the datasheet states being required not optional. NexFETS have very low Trr and suspect the di/dt plays a destructive heat part being dead band delay setting FOC InstSpin labs was set very low, (50ns). Blowing up NexFETS running the booster pack slightly above 50v may lead to unhappy customers. 

  • 0 in reply to Genatco
    TI__Guru 61280 points

    Gl,

    We will keep this in mind. To explain further, most of our customers use the 60V maximum DRV parts with 12-24 volt systems since they need headroom for things like braking. This may be why subbers aren't part of the design.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Guru 54057 points

    So there is no brake on the BoostXL board. I suppose the extra head room can allow for Qrr ringing around >45vdc - not much space left there. I've seen TIDA boards with NexFETS scope captures and there was significant ringing without snubbers. One TIDA even adds EMI filters on the UVW drives to add roll off. 

    It would be a shame to booger up such a nice board for investigating other than sine wave modulation schemes.