LDO Startup Control via Ramp Substitution Voltage
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Solution Overview
Problem
Low-dropout voltage regulators experience voltage drops across power supply batteries during startup due to high charge currents, especially when multiple regulators are connected, leading to instability and interference from parasitic diodes.
Innovation Solution
A method and system that control the start-up phase of LDO voltage regulators by replacing the reference voltage with a ramp substitution voltage, limiting charge current through the slope of this ramp, allowing simultaneous startup without voltage drops, using operational amplifiers and transistors to manage the substitution voltage and prevent interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high charge current is used to charge the external capacitor during start-up, then the regulator reaches stable operation faster, but it causes a voltage drop across the power supply battery
Solution Approach 1:
The patent applies dynamics by making the charge current variable rather than constant. The current increases over time according to a ramp function during start-up, allowing the system to balance between fast charging and minimizing voltage drop. The dynamic current profile I(t) = k*t enables the regulator to achieve stable operation quickly while controlling the instantaneous current draw from the power supply.
Solution Approach 2:
The patent changes the parameter of charge current from a fixed high value to a time-dependent ramp function. By modifying the current parameter as a function of time (I(t) = k*t), the system optimizes both start-up speed and power supply voltage stability, resolving the contradiction between fast charging and minimizing voltage drop.
2Adaptability or versatility
If multiple voltage regulators are connected across the same power supply battery, then more loads can be supplied, but the voltage drop problem is accentuated
Solution Approach 1:
The patent enables multiple regulators to operate simultaneously by using dynamic ramp-based charge currents for each regulator. This dynamic approach prevents the cumulative high-current draw that would cause excessive voltage drops, allowing versatile multi-regulator configurations without accentuating the voltage drop problem.
3Loss of energy
If the start-up of each voltage regulator is staggered to prevent voltage drop, then power supply stability is maintained, but the device complexity increases due to detailed circuit study and coordination
Solution Approach 1:
The patent implements self-service by enabling each regulator to automatically generate its own ramp-based charge current during start-up. This self-regulating mechanism eliminates the need for external coordination or complex inter-regulator control circuits, maintaining power supply stability while reducing device complexity.
4Speed
If a high charge current is used during start-up, then the external capacitor charges faster, but interference currents appear due to conducting parasitic diodes
Solution Approach 1:
The patent resolves this contradiction by using a dynamic ramp current that increases gradually over time rather than applying a sudden high current. This controlled increase in current (I(t) = k*t) charges the capacitor efficiently while keeping the instantaneous current low enough to prevent parasitic diode conduction and associated interference currents.
Data Source
AI summary
An integrated circuit including at least one low-dropout voltage regulator (LDO) capable of delivering a regulated output voltage using a reference voltage (VREF), comprises means for generating a substitution voltage (VRMP) in the form of a ramp and control means capable of replacing the reference voltage (VREF) by the substitution voltage as long as the substitution voltage (VRMP) is lower than the reference voltage (VREF).