SP6136EB datasheet(5/9 Pages) SIPEX

5 / 9 page

Rev 5/01/06

SP6136 Evaluation Manual

Page 5 of 9

LOOP COMPENSATION DESIGN

The open loop gain of the SP6136EB can be divided into the gain of the error amplifier

GAMP(S), PWM modulator GPWM, buck converter output stage GOUT(S), and feedback resistor

divider GFBK. In order to crossover at the selected frequency fc, the gain of the error amplifier

has to compensate for the attenuation caused by the rest of the loop at this frequency. The

goal of loop compensation is to manipulate the open loop frequency response such that its

gain crosses over 0dB at a slope of –20dB/dec. The open loop crossover frequency should be

higher than the ESR zero of the output capacitors but less than 1/5 of the switching frequency

fs to insure proper operation.

Since the SP6136EB is designed with ceramic type output

capacitors, a Type III compensation circuit is required to give a phase boost of 180° in order to

counteract the effects of the output LC under damped resonance double pole frequency.

Figure 11. SP6136EB Voltage Mode Control Loop with Loop Dynamic

SP6136EB 数据表(PDF) 5 Page - Sipex Corporation