Buck Regulator Architectures 4 6 Voltage Mode Buck
Buck Regulator Architectures 4. 6 Voltage Mode Buck Regulators
Voltage-Mode Regulator Output Filter Modulator Error Amplifier 2
Advantages and Disadvantages • Advantages – Stable modulation/less sensitive to noise – Single feedback path – Can work over a wide range of duty cycles • Disadvantages – – – Loop gain proportional to VIN LC double pole often drives Type III compensation CCM and DCM differences - a compensation challenge Slow response to input voltage changes Current limiting must be done separately 3
Modulator Gain 4
Output Filter d. B ZA ZB (L, Co) (Resr, Co) Hz * (Rx, Cy) indicate the components that drive the locations of the pole and the zero, detailed equations are in the notes 5
Error Amplifier The easiest place to compensate the entire loop is to adjust the compensation around the error amplifier. Several different approaches are possible. 6
Type II Compensation d. B ZF ZI ZF - Z I Hz (Rc, Cc 1) (Rc, RFB 2) (Rc, Cc 2) * (Rx, Cy) indicate the components that drive the locations of the pole and the zero (and k), detailed equations are in the notes 7
Design Guidelines for Type II Compensation • Choose a large value for RFB 2, between 2 -200 k. W • Set the mid-band gain k to give desired bandwidth • Set w. P equal to half the switching frequency: w. P = 2 p*Fsw/2 • Set wz equal to the output filter double pole w. O • Use the following equations to solve for the remaining variables 8
Type III Compensation d. B ZF ZI (RFB 2, Cc 3) Hz (Rc 1, Cc 1) (Rc 1, Cc 2) (Rc 2, Cc 3) * (Rx, Cy) indicate the components that drive the locations of the poles and zeros, detailed equations are in the notes 9
Design Guidelines for Type III Compensation • Choose a large value for RFB 2, between 2 -200 k. W • Set the mid-band gain k to shift the open-loop gain up to give desired bandwidth • Set w. P 1 equal to half the switching frequency: w. P 1 = 2 p * Fsw/2 • Set w. P 2 equal to the output filter zero, w. ESR • Set w. Z 1 and w. Z 2 equal to cancel out the output filter double pole • Use the following equations to solve for the remaining variables 10
Internal Type III Voltage Mode Compensation (LM 367 x) Internal Block Diagram Typical Application Circuit 11
Internal Type III Voltage Mode Compensation (LM 285 x) Internal Block Diagram Typical Application Circuit Internally Compensated 12
Thank you! 13
- Slides: 13