LDO Voltage Regulator Stability via Artificial Impedance
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Solution Overview
Problem
Low drop-out (LDO) voltage regulators become unstable when bond wire resistance is very low or absent, as existing solutions are complex and costly, and fail to maintain stability with minimal performance degradation or current consumption.
Innovation Solution
The solution involves splitting the main pass device into two unequal parts, with a controlled impedance in series with the smaller part, and coupling the fast feedback loop from the node between the pass device and impedance to the Miller capacitor, effectively increasing the equivalent series resistance and stabilizing the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the bond wire resistance is reduced to very low values or eliminated, then the LDO can be used with advanced package types, but the LDO becomes unstable
Solution Approach 1:
The patent introduces an artificial impedance element as an intermediary component between the pass transistor and the output node. This intermediary element simulates the bonding wire resistance that would naturally exist in traditional packages, thereby maintaining circuit stability while enabling the use of advanced package types with inherently lower or negligible bonding wire resistance.
Solution Approach 2:
The patent modifies the circuit parameters by adding a controlled impedance element with specific resistance and capacitance values. This parameter change artificially creates the equivalent series resistance (ESR) condition that the LDO stability analysis assumes, allowing the circuit to remain stable across varying output capacitance values even when actual bonding wire resistance is very low.
2Stability of the object's composition
If complex schemes are used to stabilize the LDO, then stability can be improved, but the cost and complexity increase
Solution Approach 1:
The patent segments the output capacitance effect by introducing separate artificial resistance and capacitance elements. This segmentation allows independent optimization of each parameter to achieve stability without requiring complex interconnected compensation networks, thereby maintaining relatively simple circuit topology while improving stability.
Solution Approach 2:
The patent uses simple, readily available passive components (resistors and capacitors) to solve the stability problem rather than requiring complex active compensation circuits. These basic components are inexpensive and easy to integrate, providing a cost-effective solution that avoids the complexity of sophisticated stabilization schemes.
3Stability of the object's composition
If the LDO is stabilized with artificial impedance, then stability is improved, but there may be degradation in performance or current consumption
Solution Approach 1:
The patent applies partial action by introducing artificial impedance only in the feedback path rather than in series with the main output current path. The artificial resistance and capacitance affect the stability compensation mechanism but do not directly dissipate significant power from the main current flow, thereby minimizing impact on current consumption while achieving stability improvement.
Data Source
AI summary
A low drop-out (LDO) voltage regulator which parallels a second pass device to a first pass device, where the second pass device has in series a small resistor. The small value resistor is a substitute for bond wires or capacitors with very low equivalent series resistances (ESR). A fast feedback loop is coupled to the junction of the second pass device and the small resistor and provides, via a Miller capacitor, a feedback signal to the amplifier of the voltage regulator. The added second pass device returns circuit stability by moving the fast-loop high frequency zero node back within the bandwidth of the circuit.