UCC28070A: Stability Loop Analysis

slup387.pdfHello Chuchen,

You can perform a closed loop frequency response of the system by placing a small resistor (100 Ohms or so ) in the VSENSE feedback path and injecting a signal across it. The procedure for doing this is described in this document attached.

You can also get useful loop stability information from a load transient test as described in the document below

Finally TI has a comprehensive series of control theory seminars that are most informative:

training.ti.com/control-theory-seminar-4-part-series response stability analysis&tisearch=Search-EN-Everything

Hope this helps

Regards

john

Hi,

Thank you for this information.  Customer has reviewed this information but it is very generic.  Do you have more specific info on measuring loop stability for PFC converters especially for the UCC28070A which uses current sense transformer for current sensing.

Thanks,

Chuchen 

Hello Chuchen,

I disagree with you about this document being "very generic". These documents and references describe in detail the methods of performing closed loop testing on power supplies and also describe test procedures relevant to high voltage outputs. The fact that the UCC28070A uses a current transformer to sense the FET current and uses a synthesis method to calculate total inductor current is really immaterial in terms of measuring loop performance.
Sorry I could not help.

Regards

John

Hi John,

Thank you for the material and for your support.  The customer has provided some additional feedback, can you comment on this?

"The reason I asked for specific example because UCC28070A is a PFC controller which is specifically used in an AC-DC converter. The input voltage is AC, so the operating point changes as per the instantaneous input AC voltage. More over this controller is an Average current mode controller, which consist of an outer voltage loop and an inner current loop.

The measurement of the voltage loop is quite standard, but the current loop is a bit tricky where we have to break the voltage loop since the current loop receives feedback from the current sense transformer and the reference from the voltage loop. The basics of loop measurement is you cannot measure stability consisting of multiple loops.

Also if I break the voltage loop then there is also a danger to blow up the devices and output bus cap since this is a boost converter. Moreover the overvoltage protection is combined with the output Voltage sense pin, so if we disable the output voltage loop then that will disable the OVP function as well."

-Chuchen

Hi Chuchen,

One of the manufacturers of the gain phase analysers put this document together for PFC voltage and current loop analysis.

www.bturesearch.com/documents/06.pdf

Regards

Peter