Low-dropout linear voltage source with effective compensation

Abstract

The invention discloses a low-dropout linear voltage source with effective compensation, which comprises a differential input stage A1, a voltage buffer and a power device MPPASS which are connected sequentially, wherein the positive terminal of the A1 is connected with a feedback voltage VFB; the negative terminal is connected with a reference voltage VREF which is irrelevant to a temperature and a supply voltage; a decoupling capacitor CLOAD and a loading resistor RLOAD are used as loads; a feedback unit formed by resisters RF1 and RF2 determines a value of an output voltage OUT; the low-dropout linear voltage source is also provided with a differential input stage A2; the positive terminal of the A2 is connected with the VFB, and the negative terminal is connected with the VREF; and the output of the A2 is connected with the output of the A1 through a compensation capacitor CC. A dominant pole of the low-dropout linear voltage source is reduced obviously and is 1 / betagm2R2 of the conventional structure under the condition of smaller load resistance, and a secondary pole is also increased by betagm2R2 times; and thus the dominant pole can be separated from the secondary pole effectively, the stability of LDO is enhanced, and simultaneously, the low-dropout linear voltage source is favorable for improving phase margin due to the occurrence of left-plane zero.

Description

technical field [0001] The invention relates to the field of low-dropout linear voltage source (LDO), in particular to a low-dropout linear voltage source (LDO) with effective compensation. Background technique [0002] Usually the structure of LDO is as figure 1 As shown, A1 is used as a differential input stage, and its positive terminal is connected to the feedback voltage VFB. VFB is the voltage generated by the output OUT through the voltage division of resistors RF1 and RF2. The negative terminal is connected to the reference voltage VREF that is independent of temperature and power supply voltage. At the same time, A1 Provide a certain gain to improve the line regulation and load regulation of the LDO output OUT. The input of BUFFER is connected to the output of A1, and its output is connected to the gate of the power transistor MPPASS. Its function is to reduce the influence of the pole formed by the output stage of A1 and the parasitic capacitance of MPPASS on the ...

AI Technical Summary

Problems solved by technology

[0004] The LDO of this structure has the following disadvantages: In a large load range, a large CLOAD and ESR are required to stabilize the LDO, which will increase the area of ​​the PCB and increase the cost. Poor performance and noise performance

[0011] It can be known from (3) that in R LOAD When small, p main dominated by Miller compensation, the R LOAD Larger, Miller Compensation and R LOAD C LOAD jointly decide p main , due to g mppass with R LOAD becomes larger and smaller, so the R LOAD When getting bigger, p 2 will become smaller, even close to the main pole p main , which will deteriorate the stability of the LDO

Therefore, in order to make the system stable in a wide range of loads, a large compensation capacitor CC is used, usually reaching more than 20pF; at the same time, due to the effect of Miller compensation, a zero point on the right plane will appear, and this zero point will affect the phase margin. Unhelpful

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