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TIDA-01455: TIDA-01455 LMG3410R070 Drain Slew Rate

Max Lashk
Prodigy 180 points

Part Number: TIDA-01455

In the TIDA-01455 reference design, there are different RDRV resistors for top and bottom switches. They are defining the slew rate of the transient process of the GAN switch.
In the top switch, 100k resistor is used while in the bottom switch the parallel connection of 100k and 68k resistors. If I'm understanding it correctly, it gives different slew rates for switches. Why?

Top switch:

Bottom switch:

How to choose the slew rate correctly?

By the way, in the bill of materials, there is no Q4 MOSFET which enables 68k additional resistance (while Q4 persists on the scheme). Why? Maybe it is somehow related to the first question: maybe we need only one 100k resistor without 68k in parallel?

Do we really need this transistor Q4 in a 3-phase inverter for bootstrap capacitors charge? And how to determine proper resistance in the bootstrap charging process? Maybe it will be enough to reduce the initial PWM cycle time for the bottom switches during charging?

  • 0
    TI__Expert 5120 points

    Max, hello and good morning  your query has been forwarded to our Industrial Motor Drives team for review and answer.  As is it the weekend, please give us until Monday to respond to your question.  

    Best Regards

    J. Fullilove

    Manager, Reference Design Operations

    Texas Instruments

  • 0
    TI__Prodigy 550 points

    Dear Max, 

    You may have looked at the Altium file. The Altium editor default view is showing all drawn components as present. However Altium allows variants and the variant chosen for the final board is shown in the TIDA product folder in the schematics (TIDA-01455-E1(001).pdf in the file tidrso4.zip). The link to this file is here: www.ti.com/.../tidrso4  The components are marked as "DNP" in the final schematics which is why they aren't in the BOM.

    Regards, 

    Ingolf