WHAT IS LOOP COMPENSATION？

　　Loop compensation is the adjustment of the control loop frequency response to assure loop stability and optimize the transient response of the power supply. The frequency response is determined by the gain and phase of the loop’s reaction to load current changes at all frequencies. A Bode plot is used to show the gain and phase of the frequency response.

　　LOOP COMPENSATION BASICS

　　This application note contains a brief refresher course in control loop basics. Frequency response is characterized by the effects of poles and zeros. Each pole has a corner frequency， caused by a resistance and capacitance， that determines the beginning of a 20dB/decade drop in voltage gain. The pole also causes the phase to decrease by 90°， starting roughly one decade before the corner frequency and ending about one decade after the corner frequency. A zero has the opposite effect of a pole. It causes the gain to increase by 20dB/decade starting at its “RC” corner frequency and it adds 90° of phase shift， starting one decade before the corner frequency and ending

　　The crossover frequency of the loop determines the bandwidth and transient response of the power supply. The crossover frequency is the frequency at which the loop gain is one （0dB）。 The higher the crossover frequency， the faster the power supply can respond to changes in load current.