TWM359871U - Linear regulators having fast transient response - Google Patents

Abstract

An LDO regulator includes an error amplifier, a voltage-adjusting device, a voltage-dividing circuit, and a compensation circuit. The compensation circuit, coupled to the voltage-adjusting device, is capable of providing two zeros in the loop for increasing system bandwidth and phase margin. The compensation circuit includes capacitors having small capacitance and resistors having small resistance, thereby capable of accelerating transient response for improving display quality.

Description

M359871 V. New Description: [New Technology Field] This new type relates to a linear regulator with fast transient response, especially a low-dropout regulator with fast transient response (i〇 w dropout regulator » LDO regulator) ° [Prior Art] For portable electronic products such as mobile phones, personal digital assistants (PDAs) and notebook computers, it is currently the trend to reduce the supply voltage of the core processor. In the case of bucking, system efficiency, power consumption, and battery life must also be considered. Therefore, various voltage conversion circuits are often designed for power management. A good voltage conversion circuit can provide a stable output voltage and a wide range of output current, so that when the load voltage changes instantaneously, the voltage can be quickly stabilized at the original voltage level and quickly provide different load currents. The most efficient conversion is possible. Therefore, response speed and system stability are important parameters for evaluating voltage conversion circuits. There are two traditional voltage conversion circuits: switching regulators and linear regulators (linear regUiat〇r). The linear regulators commonly used in buck applications are low-dropout regulators. Low dropout regulator, LDO regulator ). Low-dropout regulators are widely used in a variety of portable electronic products due to their low production cost, simple circuit and low noise, which provide stable output voltage. FIG. 1 is a schematic diagram of a conventional low dropout regulator 10. The low dropout voltage regulator 10 includes an error amplifier 110, a power switch 12A, a voltage dividing circuit 130, an internal compensation circuit 14A, and an output capacitor c. The low dropout regulator 10 converts the input voltage VIN to the output voltage V〇UT to drive a load (represented by resistor R1) and the load current is represented by *Iload. The voltage dividing circuit 13A includes a resistor Rd 〇 R2' to press the output voltage ν 〇υ τ * to generate a feedback voltage VFB. The error amplifier 110 includes an internal comparator 112 and an internal amplifier 14. The internal comparator 112 compares the difference between the feedback voltage vFB and a reference voltage vREF and generates a corresponding control signal, and the internal amplifier 114 can enhance the control signal. The output voltage ν 〇υ τ is stabilized by controlling the channel impedance of the power switch 12 ( (represented by the parasitic capacitance Cp in FIG. 1). The output capacitor c〇 is connected in parallel with the load resistor rl. When the load current I1〇ad suddenly changes, the output capacitor C〇 temporarily provides a large amount of current required by the load to improve the transient response of the output voltage VOUT. The internal compensation circuit 14A includes an electric P and a core and a capacitor Cz, and the resistor Rz and the capacitor Cz are connected in series with each other. One end of the internal compensation circuit 14〇 is coupled to the control end of the power switch 12〇, and the other end is coupled to the inside of the shame amplifier 110 for use as a frequency compensation. The internal compensation circuit 140 is coupled in parallel with the internal amplifier 114 to provide an equivalent large capacitance to the turn-in end of the internal amplifier 114 by the Miller effect. M359871 loop stability is an important consideration in the design of low-dropout linear regulators. The magnitude of the load current and the value of the output capacitor are two factors that primarily affect stability. Through small signal analysis, there are mainly two poles fpl and fp2 in the loop of the prior art low-dropout regulator 10, which are respectively represented by the following formula: fp\ ^ ~---- ^ X Rpar X Cpar

^tcxRsxCo and X Jtoad 2n^Co (1) -(2)

among them,

Rpar represents the equivalent output impedance of error amplifier 110 and internal compensation circuit 140;

Cpar represents the equivalent output capacitance of error amplifier 110 and internal compensation circuit 140;

Rs represents the output impedance of the power switch 120; λ represents the channel length modulation coefficient when the metal oxide semiconductor (MOS) transistor is used as the power switch 120. From (1) and (2), the main pole is known. The value of fpl is related to the error amplifier no and the internal compensation circuit 140, and the second pole fp2 changes as the load current ilQad changes. Since the phase margin of the closed loop system of the low dropout regulator requires a very low frequency main pole to be maintained, the smaller the value of 5 M359871 彳Ά fpl, the better. The low voltage drop regulator of the prior art... uses the Miller effect of the internal compensation circuit 140 to increase the value of the equivalent output capacitance and the equivalent output impedance>, thereby reducing the value of the main pole fpi: providing a larger range of phases Marginal. However, increasing the value of the capacitor will result in a longer charge-discharge time for the equivalent output capacitor Cpar, which will reduce the response to load changes and increase the peak-to-peak output voltage to a digital camera or For example, the application of the display, such a negative, temporary change _ should affect the display quality. In order to reduce the peak of the output voltage to the value of 'the low voltage drop of the prior art (4) 1G f uses the output value of the large capacitance Co (compass is 47uF~l〇〇uF), and the capacitance of this large value is c〇 The body is also expensive and will increase the production cost. [New content] This new type provides a linear regulator with fast transient response, including a 〆 error amplifier, the wire is generated according to the - reference voltage and the feedback voltage - a control signal; a series of adjustment components, coupled Connected to the error amplifier, the wire adjusts λ according to the control signal, and then generates an output voltage; the voltage dividing circuit is coupled to the electric two positive and several times, and the time is mixed to generate a grading crane; In the loop bandwidth and phase edge Z u point of the linear stabilizer, the linear stabilizer is further increased. [Embodiment] M359871 is used in the specification and the subsequent patent application scope to refer to (four) element. Those with ordinary knowledge in the field should be called by the hardware manufacturer with different nouns. The scope of the book and the subsequent patent application does not use the difference in name as the way to distinguish between the month and the month, and 1 is the difference in the function of the component. The term "including" as used throughout the specification and subsequent claims is an open term and should be interpreted as "including but not limited to". In addition, the term ', '= _ 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接 接The second device is electrically connected to the second device indirectly via other devices or connection means. At the same time, in order to make this new = more understandable, the following description of the low-voltage drop regulator specific embodiment of the present invention is described in detail with reference to the eight drawings, but the embodiments provided are not intended to limit the present invention. The scope covered. 1 Fig. 2 is a schematic view of a low-dropout regulator 2〇 in the first embodiment of the present invention. The low dropout regulator 20 includes an error amplifier 210, a power switch 220, a voltage dividing circuit 23A, and an external compensation circuit 24A. The low dropout voltage regulator 20 converts the input voltage VlN into an output voltage ν 〇υ τ to drive a load (represented by the resistor RL), and the load current is represented by Il 〇 ad. The voltage dividing circuit 230 includes a resistor core and a ruler 2, and the output voltage ν 〇υ τ can be divided to generate a feedback voltage Vfb. The error amplifier 210 includes an internal comparator 212 and an internal amplifier 214. The internal comparator 212 can compare the feedback voltage v positivity M359871 and the - reference voltage _ difference and generate a corresponding control signal, and the internal amplifier 214 can enhance the control. The signal is used to control the fine impedance of the power switch (the parasitic capacitance Cp in Figure 2 is used to stabilize the rim volts. The external compensation circuit 240 and the load resistor L, including the lightning resistance R01, R02 and capacitors c〇i, c〇2, wherein the resistor 玟(1) and the capacitor C〇 are connected in series, and the resistor R〇2 and the capacitor C〇2 are connected in series with each other.

The charge and discharge time At of the equivalent output capacitor Cpar can be expressed by the following formula, where BW represents the system bandwidth;

Cpar represents the equivalent output capacitance of the error amplifier 210; ΔV represents the voltage across the error amplifier 210;

Isr represents the current flowing through the error amplifier 210. It can be seen from equation (3) that at a fixed bandwidth, the charge-discharge time At of the equivalent output capacitor Cpar is proportional to its capacitance value. In the prior art low dropout regulator 10, the capacitance of the internal compensation circuit 140 increases its equivalent wheel: the capacitor Cpar' therefore requires a longer charging time. The novel low-dropout regulator 20 does not use an internal compensation circuit, so there is no Miller effect, so the value of the equivalent output capacitor Cpar can be reduced, thereby speeding up the response to load changes and reducing the peak-to-peak value of the output voltage. To improve quality. M359871 On the other hand, through small signal analysis, the external compensation circuit 24 can provide two zero points (zer〇) l and in the loop of the low dropout regulator 20, which are respectively represented by the following formula: Λ, fz2 1 2^x /?01xC01 1 2^xi?02xC02 where W1〇C02 and zero points fZ i and fz2 can increase the low-dropout voltage regulation _ 2 〇 bandwidth and phase margin 'Previous technology low-dropout regulator 1G needs to use large value Output Capacitor Co (usually 47uF to UF) 'The low-dropout regulator 20 of the present invention is only required to use a small capacitance (^ is usually 黯, and q is usually i and low-resistance) The resistors (R〇i and R〇2 are usually (1)) to achieve the same effect. The resistors, and can be integrated into the buckle, and the capacitance of the small capacitance c. 1 and C. 2 can be ceramic capacitors, not occupied. The circuit space is too large, so the production cost can be greatly reduced. In addition, the external compensation circuit 240 of the present embodiment includes c and r to form two zero points as compensation, "HC. 2 and R. 2, etc." The two sets of circuits increase or decrease the compensation circuit by the need of the circuit 240 to visualize the overall low voltage The zero point is formed, for example, and is composed of. The outer 4 electrician circuit 240 can be only 9 M359871. Fig. 3 is a schematic diagram of a low voltage drop regulator 30 in the second embodiment of the present invention. The device 30 is similar in structure to the low dropout regulator 20, and also has no internal compensation circuit, and also includes an error amplifier 210, a power switch 220, and a voltage dividing circuit 230, except that the low dropout regulator 30 includes an external compensation circuit. 340. The external compensation circuit 340 includes a resistor R01 and capacitors C〇i, C〇2. The series connected resistor R〇1 and capacitor C〇i are simultaneously connected in parallel with the load resistor RL, and the resistor R〇2 and the voltage dividing circuit 230 are included. The resistors Ri are connected in parallel. Through small signal analysis, the external compensation circuit 340 can provide two zero points fZ3 and fz4 in the loop of the low dropout regulator 30, which are respectively represented by the following formula: /Z3 *--- 2π x Rox x C01 r 〜1 + i?1 C〇2 Z4 2πχ R'C02 The low-dropout regulator 30 of the second embodiment of the present invention also requires only a small capacitance Cm, (: 2 and low resistance R) 〇i, you can achieve increased bandwidth and phase margin effects, and will not occupy too The large circuit space can greatly reduce the production cost. In the foregoing embodiment, the power switch 220 can be a P-channel Metal Oxide Semiconductor (PMOS) transistor, or other similar functions. The voltage divider circuit 230 can include two resistor cores and R2, or a greater number of series resistors. M359871 The novel low dropout regulator does not use an internal compensation circuit, but maintains system stability through an external compensation circuit. Therefore, the charging time of the error discharger can be reduced, thereby accelerating the transient response to improve the display quality. At the same time, the external compensation circuit only needs to use a small capacitance capacitor and a low resistance resistor, so the production cost can be greatly reduced. The above description is only the preferred embodiment of the present invention, and all the equivalent changes and modifications made by the scope of the patent application Φ should be covered by the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a low dropout regulator in the prior art. Figure 2 is a schematic view of a low dropout regulator in the first embodiment of the present invention. Figure 3 is a schematic view of a low dropout regulator in the second embodiment of the present invention. _ [Main component symbol description] 10 ' 20 , 30 low dropout regulator 110 , 210 error amplifier 112 , 212 internal comparator 114 , 214 internal amplifier 120 , 220 power switch 130 , 230 voltage divider circuit 140 internal compensation circuit 11 M359871 240, 340 Cp

Co, Cz, C〇i, C〇2 Rl, Ri, R2, Rz, R〇i External compensation circuit Parasitic capacitance Output capacitance R〇2 Resistance

12

Claims (1)

M359871 VI. Patent Application Range: 1. A linear regulator with fast transient response, comprising: an error amplifier for generating a control signal according to a reference voltage and a feedback voltage; The voltage adjusting component is coupled to the error amplifier for adjusting an input voltage according to the control signal to generate an output voltage and voltage; a voltage dividing circuit coupled to the voltage adjusting component for dividing the voltage The output voltage is used to generate the feedback voltage; and a compensation circuit coupled to the voltage adjustment component for providing a first zero (zero) and a second zero in the loop of the linear regulator, Further increasing the bandwidth and phase margin of the linear regulator. The linear regulator of claim 1, wherein the voltage regulating component comprises: a first terminal for receiving the input a second terminal coupled to the voltage dividing circuit for generating the output voltage; and a control terminal coupled to the error amplifier for receiving the control signal. 13 M359871 3. The continuation of the privilege voltage regulator as described in claim 2, wherein the compensation circuit comprises: a second valley coupled to the second end of the voltage regulating component, a first capacitor, Pure to the second end of the voltage regulating component; coupled with the first electrical-first resistor, connected in series with the first capacitor, wherein the string, the first resistor and the voltage dividing circuit are connected in parallel; and - the: And a resistor connected in series to the second capacitor, wherein the second capacitor and the second resistor connected in series are connected in parallel with the voltage dividing circuit. 4. The linear regulator of claim 3, wherein the frequency of the first zero is related to the product of the first capacitor and the first resistor, and the frequency of the second zero is related. The product of the second capacitor and the second resistor z is multiplied. 5. The linear regulator according to claim 3, wherein the capacitance of the first capacitor of the straight circuit team is about 10 times the value of the first step of the capacitance of the second resistor, and the first - The resistance and the magnitude of the second resistor are approximately equal. 6. The linear regulator according to claim 2, wherein the voltage dividing circuit comprises a plurality of series-divided voltage dividing resistors. The compensation circuit includes the linear regulator of claim 6, wherein: 14 M359871 a first capacitor coupled to the second end of the voltage regulating component and connected in parallel to the plurality of voltage dividing resistors a voltage dividing resistor; a second capacitor coupled to the second end of the voltage regulating component; and a resistor coupled in series with the second capacitor, wherein the second capacitor and resistor in series and the voltage dividing circuit in parallel. 8. The linear regulator of claim 7, wherein the frequency of the first zero is related to the product of the first capacitor and the voltage dividing resistor, i and the second zero The frequency of generation is related to the product of the magnitude of the second capacitance and the resistance. 9. The linear regulator of claim 1, wherein the voltage regulating component is a P-channel Metal Oxide Semiconductor (PMOS) transistor. 10. The linear regulator of claim 1, wherein the error amplifier does not have an internal compensation circuit. Seven, the pattern: 15