Type 3 Op-amp Compensation Network

Three types of error amplifier compensation schemes are used most often — called the Type 1, Type 2, and Type 3 in order of increasing complexity and flexibility. The former two are just a subset of the latter, so we prefer to do a Type 3 compensation to demonstrate the full scope (though often, a Type 2 compensation should suffice). 

There are two poles pi and p2 (besides the pole-at-zero pO ), and two zeros, zl and z2 provided by this compensation. Note that several of the components involved play a 

Let us take up a practical example to show how to proceed in designing a feedback loop with this type of compensation. 

Example Using a 300 kHz synchronous buck controller we wish to step down 15 V to 1 V. The load resistor is 0.2 Q (5 A). The ramp is 2.14 Vfrom the datasheet of the part. The selected inductor is 5 jiH, and the output capacitor is 330 pF with an ESR of 48 mfi. 

We know that the plant gain at dc for a buck is Vin/Vramp = 7.009. Therefore, (20 x log) of this gives us 16.9 dB. The LC double pole for a buck is at 

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