TPS40170: Compensation Design Problem

Hello,

Thank you for sharing both the schematic and the excel calculator.  Looking at the excel calculator the phase crosses zero degrees twice.  You do not want the phase to cross zero until after the cross over frequency.  

To prevent this, I would recommend changing your electrolytic output capacitor to one with a large ESR.  For example the plot below is with an ESR = 180mOhm.

Please feel free to let me know if you have any additional questions.

Best Regards,

Katelyn

Thanks for suggestion. we''l try it to see if any improvement.

However, in the Excel tool the calculation results of the zero1, zero2 and pole1, pole2 are the same, why? is there any missing on the Excel tools?

Regards,

Brian 

Hi Brian,

This is what I see:

Best Regards,

Katelyn

Hello,

In the TPS40170 Excel Tool, there are two questions about the output capacitances and output ESR?

1. In the ESR value, do i fill in it with impedance or ESR (f=0) since the working freq is about 300KHz? Please see the attached for cap material spec for your reference.

2. In the Output capacitance, how do i fill it correctly since on the boards we put 10uF x2, 47uF x2 and 0.1uF on the output rail? Is the total cap 10uF +10uF + 47uF+47uF +0.1uF correctly?

Thanks.