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TPS4811-Q1: Recommened gate resistor ?100k?

Ondrej Sereda
Prodigy 10 points
Part Number: TPS4811-Q1

Tool/software:

Hello,

so i was reading the datasheet for this component and on page 18. there is a figure 8-6 with this commentary

"Use a damping resistor R2 (~ 10 Ω) in series with C1. Equation 3 can be used to compute required C1 value for a target inrush current. A 100 kΩ resistor for R1 can be a good starting point for calculations."

R1 is the gate resistor for turning on which by this commentary is recommended 100 kOhm which seems wrong especially when you consider the R2 should be 10 Ohms - it seems that there has been a error by interchangig these two values.

In the evaulation board there is a Rg close to 10 Ohm then to 100k Ohm.

Could you clarify this value?

Thanks.

  • 0
    Prodigy 10 points

    Ok i now understand the idea why those values are there. So the tranistor is working in linear region to precharge the output capacitance.

    It has to be checked that the transistor can handle such usage.

  • 0 in reply to Ondrej Sereda
    TI__Expert 8250 points

    Hi Ondrej, 

    The 100 kohm value is just a suggested starting point. These values help with INRUSH current. If you need to limit inrush current you can rely on R2 and C1 to absorb some of the current. R2 is needed to dampen the capacitor discharge. R1 can be reduced if you need a faster turn on time, thus less INRUSH protection. The EVM is designed for a very fast turn on time. 100 kohm would be very slow. 

    You can see how these components will work together to affect INRUSH. 

    Thank you,

    Sarah