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TPS61023: Calculating Feedforward Cap

ReedKacz
Expert 3462 points
Part Number: TPS61023
Other Parts Discussed in Thread: TPS61022

Hi Team,

When looking at the TPS61023 datasheet, there are two conditions for what frequency to select the Cff value to make a zero frequency (pasted below):

For large output capacitance more than 40 μF application, TI recommends a feedforward capacitor to set the zero frequency (fFFZ) to 1 kHz. As for the input voltage lower than 1-V application, TI recommends to use the effective output capacitance is about 100 µF and set the zero frequency (fFFZ) to 1 kHz.

Are both of these supposed to be 1kHz? When looking at the TPS61022 datasheet it has a similar statement but with two different frequencies, see below:

 

For large output capacitance more than 40 μF application, TI recommends a feedforward capacitor to set the zero frequency (fFFZ) to 2 kHz. As for the input voltage lower than 2-V application, TI recommends setting the zero frequency (fFFZ) to 20 kHz when the effective output capacitance is less than 40 μF.

Thank you!

Reed

  • 0
    TI__Mastermind 34231 points

    Hi ReedKacz,

    For the first conditions of large output capacitance more than 40uF, setting the zero at 1kHz and 2kHz are the same. 

    For the second condition, in TPS61023 datasheet, it is low Vin and large Cout, so the datasheet recommends setting the zero to 1kHz. in TPS61022 datasheet, it is low Vin and low Cout, so the power stage pole 2/(2pi*Rout*Cout) is high, the zero frequency(fFFZ) doesn't need to be at 2kHZ. But if Cout is also large, I would suggest set the fFFZ at around 1~2kHz.

    You can use TPS61023 calculation tool to look at the bode plot: http://www.ti.com/product/TPS61023/toolssoftware