Class AB LDO with Dual Output Drivers for Bidirectional Current
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Solution Overview
Problem
Low-dropout regulators (LDOs) face challenges in achieving bidirectional current capability while maintaining low power consumption and stability, especially when sourcing and sinking currents, due to large impedance nodes and parasitic elements, which complicates the design and increases power dissipation.
Innovation Solution
The LDO design incorporates two output drivers in a class AB configuration, where only one driver is operational in high conductivity mode while the other is in low or non-conductive state, depending on the operating mode, and both drivers are minimized to low conductivity when unloaded, using a current generator unit and input amplifier stage to control the drivers' states based on input signal levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If bidirectional current capability (sourcing and sinking) is added to the LDO, then the current capability is improved, but the power consumption increases due to both output drivers being operational
Solution Approach 1:
The patent implements dynamic switching between sourcing and sinking modes by controlling the conductivity of first and second output drivers based on operating conditions. The class AB configuration allows the LDO to adaptively switch which driver is active, minimizing power consumption while maintaining bidirectional capability. This is achieved through control circuits that adjust driver conductivity in response to load requirements and operating state.
2Power
If both output drivers are made large to ensure drive capability, then the drive capability is improved, but the impedance nodes and parasitic elements increase
Solution Approach 1:
The patent segments the output stage into first and second output drivers that operate in complementary fashion. Instead of using one large bidirectional driver, the design divides the function into two specialized drivers that can be independently controlled. This segmentation reduces the size and complexity of individual driver components while maintaining overall drive capability through coordinated operation.
3Adaptability or versatility
If the output branch uses series connection of two large devices for bidirectional capability, then the current capability is improved, but the bias current control becomes critical and power dissipation increases
Solution Approach 1:
The patent applies local quality by making the first and second output drivers have different conductivity characteristics optimized for their respective functions. The first driver is optimized for sourcing current while the second is optimized for sinking current. This asymmetric design allows each driver to operate efficiently in its designated mode, reducing overall power dissipation compared to using two identical large devices.
Data Source
AI summary
A low-dropout regulator comprises an output current branch (100) in which a first output driver (110) and a second output driver (120) is arranged. An input amplifier stage (200) provides a first control current (I1) to control the operating state of the first and the second output driver (110, 120). A current generator unit (300) provides a second control current (12) to operate the first output driver (110) in the second operating state and provides a third control current (13) to operate the second output driver (120) in the second operating state, when the first control current (I1) of the input amplifier stage (200) is below a threshold level.