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# UCC28180: selected the right PFC Choke

Part Number: UCC28180

When dimensioning a PFC circuit based on UCC28180, we will use the excel tool from TI.
When calculating the technical parameters of the PFC choke, the maximum peak current IL_PEAK is 17.5A and the boost inductor value LBST is 0.130mH. How should this information be understood?

In the data sheets of PFC chokes, the inductance is often specified at a saturation current and a nominal current.

In this case, must a PFC choke be selected which has 0.13mH at saturation current (17.5A) or at the nominal value?

Or how should the PFC choke generally be selected?

Translated with DeepL.com (free version)

• Hello John,

In the UCC28180 Excel tool, IL_PEAK is the peak of the ripple current at the peak of the AC-line current at lowest input voltage at full load power.
This is the maximum current that the inductor will see on a steady-state basis and is used for inductance design and core loss estimation.

To prevent core saturation, design the inductor to the maximum peak current under overload conditions when Peak-Current-Limit (PCL) function is operating.
This Ipk_pcl is calculated as shown in datasheet equation (3):

where Vpcl = -0.4V (typical).

In your case, the PFC inductor should be selected or designed to have 0.13mH at the nominal peak operating current of 17.5A.
The saturation current specification of the inductor should be significantly higher than this nominal current, and higher than Ipcl.

Regards,
Ulrich

• Hi Ulrich
The Excelt tool gives me a value of 14mR for the R_SENSE. According to the formula given, ipk_pcl is 11.4A. How do I select the PFC choken now? 17.5A or 11.4A?

• Hello John,

Your question has revealed an inconsistency in the UCC28180 datasheet.

It seems that the Vpcl value to be used for Equation (3) is 1V, not 0.4V, as seen in the Functional Block Diagram:

0.4V is the equivalent magnitude of the PCL threshold at the ISENSE input.  1.0V is the actual Vpcl threshold at the PCL comparator.
So, (1V/2.5)/14mR = 28.6Apk.

Therefore, design/select the boost inductor so that it has ~130uH at 17.5A and does not go into hard saturation if the current ever reaches 29~30A.

TI will make a correction to the equation the next time that the datasheet is revised. (But, I can't predict when that will be.)

Regards,
Ulrich