AN557 datasheet(16/52 Pages) STMICROELECTRONICS

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AN557 APPLICATION NOTE

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Figure 15. Compensation network of the error amplifier

The Bode diagram is shown in fig.16.

Figure 16. Bode plot showing gain and phase of compensated error amplifier

The compensation circuit introduces a pole at low frequency and a zero that is generally calculated to be

put in the proximity of the resonance frequency of the output LC filter.

The second pole at high frequency generally falls in a zone of no interest (for the system stability, one must

consider the zero introduced by ESR characteristic of the output capacitor. Not all the designers agree on

this solution).

If necessary, however, one can turn to more sophisticated compensation circuitry. An example is shown

in fig. 17.

Figure 17. One pole, two zero compensation network

Such a circuit introduces a pole at low-frequency and two zeros.

Π R1 C1

-----------------------------

Π R2 C2

-----------------------------

AN557 bảng dữ liệu(PDF) 16 Page - STMicroelectronics