TPSF12C1-Q1: question about AEF design tool excel

Hi Jay,

For common-mode noise, the applicable noise source impedance is typically capacitive in nature and represents the parasitic coupling of the switch node(s) dv/dt to the Earth ground (which is the large copper ground plane in a typical EMI measurement setup).

You could leave the default values in the file as it shouldn't significantly affect the subsequent calculations. This is true especially as the regulator-side Y-caps appear in parallel with the noise-source impedance when considering the equivalent circuit for loop-gain calculation. The Y-caps are typically > 1nF each, so they should dominate the impedance characteristic/behavior.

Regards,

Tim

For more detail on noise-source impedance measurements, here are some references to review:

https://ieeexplore.ieee.org/document/867670

https://ieeexplore.ieee.org/document/4016388

https://ieeexplore.ieee.org/document/1296763

The first link here uses a simple method with EMI measurements with and without a reference CM choke installed at the power lines. The CM noise source impedance can then be calculated from the choke impedance and the insertion loss of the choke.

No problem, thanks Jay.