Split-Pass LDO Circuit for Smooth Load Transition Stability
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Solution Overview
Problem
Low dropout linear regulators (LDOs) with low quiescent current (Iq) face challenges in transient response and stability due to low biasing of the error amplifier, leading to slow transient response and instability issues, particularly at light loads, which are exacerbated by the need for impractical compensation components in area-constrained designs.
Innovation Solution
A low dropout regulator (LDO) circuit topology with split pass transistors and a control circuit that provides smooth pass current transitions as a function of load current, utilizing a first, second, and third pass transistor with different sizes and controlled gate drive signals according to continuous conduction curves, reducing quiescent current and enhancing stability without complex load current sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the error amplifier is biased with low current (1-10 nA) to reduce quiescent current, then power consumption is reduced, but transient response becomes slow and stability issues occur
Solution Approach 1:
The pass transistor is divided into two separate transistors (first pass transistor and second pass transistor) with different sizes. The first pass transistor handles light load conditions while the second handles heavy load conditions, allowing the error amplifier to operate at low bias current for extended battery life while maintaining stable transient response across different load conditions
Solution Approach 2:
The circuit dynamically switches between the first and second pass transistors based on load conditions. The control circuit adjusts which transistor is active depending on whether the load is light or heavy, enabling the system to optimize between low power consumption at light loads and stable transient response at heavy loads
2Power
If a single large pass transistor is used to handle heavy load current, then power delivery capability is improved, but gate pole frequency becomes too low causing instability at light loads
Solution Approach 1:
The single large pass transistor is segmented into two transistors with different sizes. The first pass transistor has a size optimized for light load operation with higher gate pole frequency, while the second pass transistor has a larger size for heavy load capability. This segmentation allows each transistor to operate in its optimal range without the stability issues of using a single oversized transistor
Solution Approach 2:
Different pass transistors with different physical characteristics (sizes) are used for different operating conditions. The first pass transistor is sized appropriately for light load conditions, while the second is sized for heavy load conditions, ensuring optimal performance and stability in each local operating regime
Data Source
AI summary
A system includes a battery. The system also includes a low dropout regulator (LDO) circuit with an input coupled to the battery and the LDO circuit. The system also includes a load coupled to an output of the LDO circuit. The LDO circuit includes an error amplifier and a control circuit coupled to the error amplifier. The LDO circuit also includes a first pass transistor coupled to the control circuit and configured to provide a first pass current as a function of load current according to a first continuous conduction curve. The LDO circuit also includes a second pass transistor coupled to the control circuit and configured to provide a second pass current as a function of load current according to a second continuous conduction curve.