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# UC3842: Slope calculation for inductor pole in Buck converter

Part Number: UC3842

Hello TI E2E,

I am using UC3842 to control Buck converter in current control mode,

I am using SLUP340 to design feedback compensator

it requires me to calculate WL i.e. pole due to inducator of Buck converter.

for my first design i do not intend to use slope compensation, how do I deal with the procedure mentioned in SLUP340 (screenshot attached below) to calculate WL?

Vin =42-54V

Vo= 12V

Io=5A

L=200uH

C=60uF

Resr =20m Ohm.

• You can also consider Understanding and Applying Current-Mode Control Theory and download and try TI Power Stage Designer which has a built in control loop modelling tool you can use to compare against your calculated model.

Steve

• Hello, Steven,

I do have both the things mentioned by you.

I am comparing my model with TI power stage calculator, but it is not matching in magnitude but matching in shape. (I am using MATLAB to generate bode plots)

I understand that the underlying reason for that is I am clueless about the value of current, shunt, gain, used by the model which affect calculation of Avm and Rcomp, Ccomp. Refer SLUP340.

Hence while retrospecting on my MATLAB code to generate Bode plot i came across my initial query.

• If the shape (frequency break points) of your model result is the same as the shape of the result from TI Power Stage Designer but the magnitude is not matching, this is a good start. It is likely your model is off by some gain term. You could brute your result to match the TI Power Stage Designer result and then you will know how much gain is missing from your model. Also, don't forget to include the current sense gain term inside the PWM as well as the CS gain resulting from the external resistor (Ri), CS xfmr or whatever method you are using to sense and sample the current.

• Hello Steven,

I do have included current gain term.

I do get the power stage Rout, Cout pole same as that of Ti also the zero of Resr and Cout.

Only thing I wanted to know more about was how the high frequency pole of inductor need to be included in the model.

I am aware that it is high frequency pole and will not affect much on the control practically. But i am curious on how to compute that for design.

• Hi,

The application note shows how to calculate WL, and how it is facterized into the transfer function. So please make your question specific which in the equation you are not sure how to do.

• I do not want to include slope compensation for 1st design iteration can i ignore WL?

• Hi,

You can ignore WL if not using the slope compensation.