Fast Feedback Loop for High-Current LDO Load Transients
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Solution Overview
Problem
High current circuits, such as low dropout (LDO) regulators, face challenges in minimizing voltage drops due to bond wire resistance, metallization resistance, and substrate routing resistance, which degrade load transient performance and lead to instability.
Innovation Solution
Incorporating a separate fast regulation loop with a single bond wire and a stabilization circuit that includes parasitic resistances within the loop, using a separate pad for feedback, and connecting a small resistor to the fast feedback pad to mitigate parasitic contributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If two bond wires are used to reduce bond wire resistance, then voltage drop due to bond wire resistance is reduced, but device complexity and parasitic contributions from additional bond wires remain
Solution Approach 1:
The patent converts the harmful parasitic resistances (bond wire resistance, metallization resistance, substrate routing resistance) into a beneficial element by including them within the fast regulation loop. The stabilization circuit uses these parasitic resistances as part of the feedback mechanism, transforming what was previously a source of instability into a controlled element that improves load transient response.
2Area of stationary object
If package size is reduced, then integration density increases, but bond wire resistance and parasitic contributions increase
Solution Approach 1:
The patent segments the regulation function into two separate loops: a fast regulation loop that handles dynamic load transient response and includes parasitic resistances, and a standard regulation loop for steady-state operation. This segmentation allows the fast loop to compensate for voltage drops caused by reduced package size and shorter bond wires, maintaining performance despite physical constraints.
Solution Approach 2:
The patent implements a feedback mechanism where the output voltage is monitored and fed back to the error amplifier. The stabilization circuit adjusts the control signal based on the voltage drop detected across the parasitic resistances, continuously compensating for their effect and maintaining stable output voltage despite package size reductions.
3Power
If high supply currents are provided, then circuit functionality increases, but voltage drop due to metallization resistance and substrate routing resistance increases
Solution Approach 1:
The fast regulation loop continuously monitors the output voltage and compensates for voltage drops caused by high supply currents flowing through metallization and substrate routing resistances. The error amplifier adjusts the control signal based on the detected voltage drop, ensuring stable output voltage even at high current levels.
4Stability of the object's composition
If parasitic resistances are excluded from the regulation loop, then stability improves, but load transient response deteriorates
Solution Approach 1:
The patent creates a separate fast regulation loop specifically for handling load transient responses. This segmented approach allows the fast loop to include parasitic resistances and respond quickly to transient changes, while the main regulation loop maintains overall stability. The two loops operate at different speed levels and handle different aspects of regulation.
Solution Approach 2:
The patent implements dynamic regulation by creating a fast response loop that actively adapts to changing load conditions. The stabilization circuit modifies the control signal in real-time based on the instantaneous voltage drop across parasitic resistances, enabling the system to respond dynamically to load transients while maintaining stability through the layered loop structure.
Data Source
Figure 1~2
Figure 3a
Figure 3b
AI summary
Circuits and methods to improve dynamic load transient performance of circuits supplying high current and having parasitic resistances are disclosed. These circuits comprise e.g. LDOs, amplifiers or buffers. The circuits and methods are characterized by including parasitic resistances, caused by bond wires, metallization of pass devices, and substrate routings, in a loop for fast transient response. Furthermore the circuits comprise a stabilization circuit within said loop and a separate pad for said loop.