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LMG34XX-BB-EVM: Maximum Rise Time and Fall Time

ANIL KIRIKKAYA
Prodigy 50 points
Part Number: LMG34XX-BB-EVM

Hi. We are trying to acheive the rise time and fall time <=2ns at 200V. We want to know if it is possible with this board (we can provide subnanosecond rise time pwm signal) 

  • 0
    TI__Genius 16390 points

    Hello Anil,

    The slew rate for turn on can be adjusted to be 100V/ns by changing the rdrv resistor to 10kohm.The turn off time will be highly depending on the load current as the current will be charging the capacitor after turn off.

    Hope this helps.

    Regards,

  • 0 in reply to Yichi Zhang.
    Prodigy 50 points

    Thank you for reply. Right now we have your mother and doughter board and we are driving it with a signal generator. But we can't get 100v/ns rise time. I think it might because of our signal generator is not that fast. In lgm3410 datasheet  they have achieved 102V/ns. To do this what kind of driver should we use?  Or as you answered should we adjust rdrv resistor ? Can you explain it in more detail?

  • 0 in reply to ANIL KIRIKKAYA
    TI__Genius 16390 points

    Hello Anil,

    Could you verify the Rdrv resistor value on the daughter card? It should be around 15k to give you 100V/ns turn on slew rate. 

    Regards,

  • 0 in reply to Yichi Zhang.
    Prodigy 50 points

    It is already 15k. But we still can't get 100v/ns. What I really ask was is it important what are we driving the board with? Signal generator has 5v/3ns rise time. 

  • 0 in reply to ANIL KIRIKKAYA
    TI__Genius 16390 points

    Hello Anil,

    Theoretically it should not. There is a threshold for the input signal - as soon as it goes over the threshold (around 2.5V), the driver will turn on the FET. One thing I noticed is that the bus voltage is at 200V. The max slew rate of 100V/ns is observed when bus voltage is at 400V, and it would be less with lower bus voltage because the capacitances will be larger with lower bus voltage. What's the slew rate you are currently observing? 

    Regards,