Voltage-mode switching dc-dc converter with on-chip frequency compensation

Abstract

An on-chip frequency-compensated voltage mode switching DC-DC converter relates to the field of analog integrated circuits. The present invention includes an error amplifier, a PWM comparator, an oscillator, a logic control module and a power tube, the power tube has a function for inputting a variable DC voltage The VIN input terminal of VIN also includes a feedforward compensation module. The output end of the feedforward compensation module is connected to the negative input end of the error amplifier. The output end of the feedforward compensation module is also grounded through the second resistor Rf2, and the output of the feedforward compensation module is connected to the ground. The terminal is also connected to the output terminal of the error amplifier through the third resistor Rf3, and the output terminal of the feedforward compensation module is connected to the output voltage Vsense through the first resistor Rf1. Under the condition of ensuring the stability of the loop, the invention realizes the full integration of the compensation components on the chip, saves the PCB area, and reduces the application cost.

Description

technical field [0001] The present invention relates to the field of analog integrated circuits, in particular to a voltage mode switching DC-DC converter with an on-chip frequency compensation structure. Background technique [0002] Switching DC-DC converter is an important part of power management circuit, it is used to convert variable input DC voltage to fixed output DC voltage. Compared with LDO voltage regulator, switching DC-DC converter has high efficiency High advantage, it is one of the preferred power supply systems for portable products. [0003] The schematic diagram of the traditional voltage-mode switching DC-DC converter is shown in Fig. figure 1 As shown, it consists of reference voltage, oscillator, error amplifier, sampling resistor, PWM comparator, logic control, power tube, external compensation network and LC filter network. The output voltage is fed back to the error amplifier after the sampling resistor network is divided The reverse input terminal...

AI Technical Summary

Problems solved by technology

Since the error amplifier of this control loop works in an internal open-loop state, the loop gain of the system is not fixed, and the inductance L O and output capacitor C O The formed LC filter network will produce double poles, which will cause the phase of the system to change rapidly and produce a ‐180° phase shift. When the system is subject to various interferences such as loop DC gain changes, loop unity gain bandwidth changes, feedback loop oscillations, and noise, etc. Triggered by factors, it is easy to generate loop oscillation

[0004] Therefore, in the design of the switching DC-DC converter, it is necessary to add a compensation network to ensure system stability. The traditional switching DC-DC converter compensation network is composed of passive resistors and capacitors. Since the compensation capacitor is usually relatively large, it is difficult to Integrated, so the compensation network is usually implemented with off-chip discrete devices, which increases the area of ​​the PCB board and the number of pins of the chip, while increasing the application cost, limited to the current trend of miniaturization and low cost of portable products, for switching DC-DC The converter puts forward new requirements, and the external compensation components should be as simple as possible, and can be fully integrated inside the chip to save PCB area and peripheral component costs

[0005] At present, the commonly used internal frequency compensation methods mainly include active capacitance and active resistance schemes based on constant transconductance amplifiers and capacitance multipliers, but the multiplication magnification of active capacitance is limited, the maximum is 100 times, when the compensation capacitance is large , the on-chip capacitance is still very large, which is not easy to integrate. At the same time, the amplification factor is seriously affected by device matching and process parameters. The active resistance is affected by the transconductance of the operational amplifier. The actual resistance is difficult to accurately control, and the design of the active compensation network is difficult. The system is not easy to stabilize

Images