UCC28C42: Slope Compensation for a Buck Converter

Keith Keller

Part Number: UCC28C42
Other Parts Discussed in Thread: INA181

Hello,

Would the slope compensation circuit shown in Figure 27 of the UCC28C42 datasheet also work for a buck converter topology?

Thank you, Keith

0 John Griffin1 over 5 years ago

Hello Keith,

You can use that circuit with a forward converter which is just another name for a transformer coupled buck converter.

The difficulty with the buck converter is that the switch current is not referenced to ground.

As in the drawing below:

So the figure you attached is not suitable for this type of buck circuit.

Regards

John

0 Keith Keller over 5 years ago in reply to John Griffin1

Thanks John.

Are you saying we could add in current shunt like the INA181 to reference current on the high-side?

Or is it not possible to do buck converter slope compensation?

0 John Griffin1 over 5 years ago in reply to Keith Keller

Hello Keith,

Your question was whether the circuit your referenced was suitable for a buck converter.

My answer was that you will not see this circuit in a buck.

But youu will need slope compensation for current mode control whenever the duty cycle is greater than 50%

As far as I know the INA181 has a very low bandwidth so it is not suitable for sensing the fast rising edges of the switching current.

You can use a resistor shunt sensor followed by a differential amplifier to implement current sensing in the buck circuit.

This is what the block a1 in the attachment above is trying to show.

Sorry for any confusion

Regards

John

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