Adaptive LDO Load Sharing With Internal and External Pass Elements
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Solution Overview
Problem
LDO voltage regulators face issues with power dissipation, thermal management, and bandwidth limitations due to varying load conditions, particularly when load currents increase, which can damage the die and require complex thermal management solutions.
Innovation Solution
An LDO voltage regulator system with integrated and external pass elements that adaptively share load current using load sharing circuitry, allowing seamless transfer between internal and external pass elements through variable impedance dividers and error amplifier control, enabling efficient load handling without external components and maintaining stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the pass element size is increased to handle higher load currents, then the current handling capability is improved, but the die area and thermal management complexity increase
Solution Approach 1:
The patent divides the current handling function into two separate pass elements: an internal pass element for light load conditions and an external pass element for heavy load conditions. This segmentation allows each element to be optimized for its specific operating range, with the external element handling high currents without requiring excessive die area since it operates outside the integrated circuit.
2Power
If the pass element size is increased to handle higher load currents, then the current handling capability is improved, but the thermal management complexity increases
Solution Approach 1:
The patent extracts the heavy load current handling function from the integrated circuit by using an external pass element. This removes the thermal management burden of high-power dissipation from the sensitive die, leaving only the low-power internal pass element on-chip that requires minimal thermal management while the external element handles the thermal load separately.
Solution Approach 2:
The patent implements dynamic switching between internal and external pass elements based on load conditions. The error amplifier and control circuitry automatically transition between elements as load current varies, ensuring the internal element handles light loads and the external element handles heavy loads, thereby optimizing thermal performance across the entire operating range.
3Device complexity
If a single pass element is used to handle all load conditions, then the device complexity is reduced, but the bandwidth and response time deteriorate under varying load conditions
Solution Approach 1:
The patent employs dynamic switching between internal and external pass elements based on real-time load conditions. The error amplifier monitors the load and automatically transitions between elements, allowing the circuit to optimize bandwidth for light loads (using the fast internal element) and handle heavy loads (using the high-current external element), thereby maintaining high performance across the entire operating range.
4Ease of manufacture
If the internal pass element handles all loads, then the external components are minimized, but the power dissipation and thermal stress on the die increase
Solution Approach 1:
The patent segments the power handling function between internal and external pass elements. The internal element handles only light loads with low power dissipation, while the external element handles heavy loads with high power dissipation. This segmentation protects the die from excessive thermal stress while still utilizing external components only when necessary for heavy load conditions.
Data Source
AI summary
Load sharing techniques for voltage regulators. In an example, the techniques may be implemented in an LDO voltage regulator configured to provide load sharing with a single driver for internal and external pass elements using a pair of variable voltage dividers to adjust the load sharing based on load current. In other examples, a calibrated voltage source can be used to replace one of the variable voltage dividers. Calibration circuitry and methodologies for determining the value of the calibrated voltage source are also described. In still other examples, a single variable voltage divider can be used, with no calibrated voltage source, by constraining the external pass element to be weaker than the internal pass element. In any such examples, the internal and external pass elements can be implemented, for instance, with either n-type or p-type power transistors, and with similar transistor technologies or diverse transistor technologies (e.g., FETs and BJTs).