Op-Amp Current Limiting for LDO Brownout Prevention
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Solution Overview
Problem
Operational amplifiers in Low Drop Out (LDO) voltage regulators face brown out conditions due to substantial current sourcing from current-limited supplies, which can lead to unsafe undervoltage events, especially when shared among multiple regulators in a Power Management Integrated Circuit (PMIC).
Innovation Solution
A current limiting circuit is implemented within the operational amplifier to regulate the loading of a limited current supply using a variable current source, comparing sensed loading to a current reference to prevent excessive current sourcing and thus prevent brown out conditions by limiting the maximum allowable current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the operational amplifier sources substantial current from the current-limited supply to meet load regulation requirements, then the bandwidth and load regulation performance are improved, but the supply voltage drops causing brown out conditions
Solution Approach 1:
The patent implements a feedback mechanism where the output of the operational amplifier is fed back through a feedback network to the inverting input. This feedback loop allows the system to automatically adjust and limit the current drawn from the current-limited supply, preventing brown out conditions while maintaining the required bandwidth and load regulation performance.
Solution Approach 2:
The patent changes the operating parameters of the operational amplifier by introducing current limiting circuitry that dynamically adjusts the current draw from the current-limited supply. This parameter adjustment ensures the supply voltage remains stable and prevents brown out conditions while maintaining adequate bandwidth for load regulation.
2Adaptability or versatility
If multiple LDO voltage regulators share the same current-limited supply, then the power management integration is improved, but the brown out condition is aggravated
Solution Approach 1:
The patent segments the current draw from the current-limited supply by implementing individual current limiting circuitry within each LDO voltage regulator. This segmentation allows each regulator to manage its own current consumption independently, preventing any single regulator from causing brown out conditions that would affect other shared regulators.
3Speed
If the operational amplifier draws excessive current during startup or overcurrent events, then the transient response capability is improved, but the supply voltage drops causing unsafe undervoltage events
Solution Approach 1:
The patent applies preliminary anti-action by implementing current limiting circuitry that proactively prevents excessive current draw during startup and overcurrent events. This preliminary protection mechanism stops the harmful effect (excessive current) before it can cause supply voltage drops and unsafe undervoltage events, while still allowing adequate transient response capability.
Data Source
AI summary
A method for current limiting an operational amplifier includes sensing a first current through a first branch of the operational amplifier. The first branch conducts the first current from a limited current supply connected to an operational amplifier output. The first current is compared to a reference current to generate a regulation signal. A variable current source is controlled with the regulation signal. An output current of a transconductance amplifier is limited with the variable current source to limit the first current in response thereto.