Loop Compensation of MIC2204 Behzad Mohtashemi EE 136 Power Electronics Professor Zhou Ph.D.

WHAT IS MIC 2204? It is a high-efficiency 2MHz Synchronous Buck Converter. >95% efficiency It is a high-efficiency 2MHz Synchronous Buck Converter. >95% efficiency Input voltage range: 2.3V to 5.5V Input voltage range: 2.3V to 5.5V Output down to 1V/600mA Output down to 1V/600mA It has ultra-fast transient response (typical 200kHz GBW) It has ultra-fast transient response (typical 200kHz GBW) Internal Compensation Internal Compensation All ceramic capacitors ( No ESR ). difficult to compensate All ceramic capacitors ( No ESR ). difficult to compensate

MIC2204 Block Diagram

Stable_Unstable_System

How to Make an Unstable System, Stable.

Problems of Making a Voltage_Mode_Buck_Converter Stable

Remedies Close the loop before the resonant frequency, but this will result in a very slow transient response. Close the loop before the resonant frequency, but this will result in a very slow transient response. Use an output capacitor with a small ESR, such Y5_ceramic capacitors. Use an output capacitor with a small ESR, such Y5_ceramic capacitors. Add zeroes into your loop system, by using typeII and typeIII amplifiers. Add zeroes into your loop system, by using typeII and typeIII amplifiers. MIC2204 uses a zero amplifier to introduce the final zero into the system. The first pole and zero come from the error amplifier itself. MIC2204 uses a zero amplifier to introduce the final zero into the system. The first pole and zero come from the error amplifier itself.

Whenever two different paths will lead to the same point, then we will have zeroes.

Compensation Configuration in MIC2204

Structure of Error Amplifier

Zero Amplifier It is simple unity gain amplifier It is simple unity gain amplifier It only needs to create an alternate path to the output It only needs to create an alternate path to the output It needs no internal compensations It needs no internal compensations By creating an alternate path, then it will boost both gain and phase By creating an alternate path, then it will boost both gain and phase

Overall Stability

References H. Dean Venable, The K factor: A new mathematical tool for stability analysis and synthesis, Powercon, 10, H1-H12 (1983) H. Dean Venable, The K factor: A new mathematical tool for stability analysis and synthesis, Powercon, 10, H1-H12 (1983) Thomas V. Papathomos, On the stability of peak current-controlled converters: Analysis, simulation, and experiments, IEEE Transaction on Industrial Electronics, IE-33(2), (1986) Thomas V. Papathomos, On the stability of peak current-controlled converters: Analysis, simulation, and experiments, IEEE Transaction on Industrial Electronics, IE-33(2), (1986) J. Kassakian, M. Schlecht, and G. Verghese, Principles of Power Electronics. Reading, MA: Addison Wesley, 1992 J. Kassakian, M. Schlecht, and G. Verghese, Principles of Power Electronics. Reading, MA: Addison Wesley, 1992

Overall Stability