LDO Driver Circuit Gate Voltage Adjustment for Dropout and Leakage
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Solution Overview
Problem
Low dropout regulators (LDOs) face a challenge in achieving small voltage drop while minimizing power transistor size, as increasing transistor size leads to higher quiescent current and current leakage, which is undesirable in portable devices, and reducing leakage current compromises dropout performance.
Innovation Solution
A driver circuit with two parallel paths, one using an NMOS transistor and the other a PMOS transistor, is used to dynamically adjust the gate voltage of the power MOSFET, allowing the LDO to switch between paths based on load conditions, reducing voltage dropout and leakage current without increasing transistor size or quiescent current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the power transistor size is increased to achieve small dropout voltage, then the dropout voltage is reduced, but the quiescent current and current leakage increase
Solution Approach 1:
The patent implements dynamic adjustment of the power transistor gate drive voltage based on load conditions. The driver circuit switches between two paths: one optimized for high load current (providing strong drive to keep transistor fully open for low dropout) and another for low/no load conditions (reducing gate voltage to minimize leakage current). This dynamic adaptation resolves the contradiction by optimizing transistor operation for each operating condition rather than using a fixed-size transistor that compromises both scenarios.
Solution Approach 2:
The patent changes the gate voltage parameter dynamically based on load conditions. The driver circuit monitors load current and adjusts the gate voltage magnitude accordingly - applying higher gate voltage during high load to maintain low dropout, and reducing gate voltage during low load to minimize leakage. This parameter adjustment allows the same power transistor to achieve low dropout when needed while minimizing energy loss when load is light.
2Temperature
If the power transistor size is increased to improve dropout performance, then the dropout voltage is reduced, but the integrated circuit space occupied increases
Solution Approach 1:
The patent uses dynamic gate drive adjustment to enable a smaller power transistor to achieve low dropout performance. By optimizing the gate voltage in real-time based on load conditions, the system extracts maximum performance from a compact transistor, eliminating the need for large physical transistor area while maintaining low dropout voltage.
Solution Approach 2:
The patent achieves low dropout with reduced transistor area by changing the gate voltage parameter dynamically. The driver circuit provides enhanced gate drive when needed, allowing a smaller transistor to maintain adequate channel conductivity for low dropout performance, thus reducing the area occupied in the integrated circuit while meeting dropout specifications.
3Loss of energy
If the power transistor size is reduced to decrease leakage current, then the quiescent current is reduced, but the dropout voltage increases
Solution Approach 1:
The patent implements a dynamic driver circuit that adapts its output based on load conditions. For small transistors operating under high load, the driver provides enhanced gate voltage to ensure the transistor is fully open, achieving low dropout despite the small device size. During low load conditions, the driver reduces gate voltage to minimize leakage current from the small transistor. This dynamic control enables small transistors to achieve both low leakage and low dropout performance.
Solution Approach 2:
The patent changes the gate voltage parameter dynamically to compensate for the smaller transistor size. The driver circuit detects load conditions and adjusts gate voltage magnitude accordingly - applying higher gate voltage during high load to maintain low dropout with the small transistor, and reducing gate voltage during low load to minimize leakage. This parameter adaptation allows small transistors to overcome their inherent limitations.
Data Source
AI summary
An electronic device includes a low drop-out regulator for providing a regulated output voltage. The low drop-out regulator generally comprises a power MOSFET transistor having a gate coupled to a driver. The driver has a first path including an NMOS transistor and being coupled to the gate of the power MOSFET, a second path having a PMOS transistor and being coupled to the gate of the power MOSFET, and a switch for alternately switching between the first and second paths so as to provide a voltage to the gate of the power MOSFET ranging from ground to a power supply level.