Variable-Slew LDO Regulator for Output Voltage Spike Reduction
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Solution Overview
Problem
Low-dropout regulators (LDOs) experience significant regulated output voltage spikes when the output current changes, particularly due to the increased transconductance of power devices at higher currents, leading to supply line disturbances and voltage fluctuations.
Innovation Solution
The LDO incorporates an input amplifier stage that adjusts the slew rate of the control voltage applied to the output driver, increasing the slew rate when the output current is small to reduce voltage spikes while maintaining minimal supply current derivative, thereby minimizing disturbances on the supply line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the output driver responds faster to reduce regulated output voltage spikes, then the response speed improves, but the supply current derivative increases causing larger disturbances on the supply line
Solution Approach 1:
The patent applies dynamics by making the slew rate of the control voltage variable rather than fixed. The input amplifier stage dynamically adjusts the slew rate based on operating conditions, allowing faster response when needed while limiting supply current derivative under other conditions. This is achieved through circuit configurations that automatically modify the charging/discharging rate of the control connection depending on the state of the LDO.
Solution Approach 2:
The patent changes the parameter of slew rate from a constant value to a variable parameter that can be adjusted based on operating conditions. By modifying the slew rate parameter of the control voltage applied to the output driver, the system optimizes the trade-off between response speed and supply current derivative, resolving the technical contradiction.
2Object-generated harmful factors
If the control voltage is charged/discharged under slew rate limitation to minimize supply current derivative, then the supply line disturbance reduces, but the response of the output driver becomes slower increasing regulated output voltage spikes
Solution Approach 1:
The patent makes the slew rate limitation dynamic rather than static. Instead of applying a fixed slew rate limit in all conditions, the input amplifier stage adjusts the slew rate based on the operating state of the LDO, allowing the system to have fast response when needed while maintaining supply line stability under normal conditions.
Solution Approach 2:
The patent changes the slew rate parameter from a fixed limiting value to an adjustable parameter that varies with operating conditions. This allows optimization of both supply line disturbance and response speed by adapting the slew rate to the specific situation rather than being constrained by a single fixed value.
3Measurement precision
If the power device transconductance is increased to improve regulation sensitivity, then the regulation performance improves, but the regulated output voltage spikes increase when output current changes
Solution Approach 1:
The patent applies periodic action through the time-dependent control of the slew rate. The input amplifier stage provides different slew rates during different phases of operation, particularly during transient conditions versus steady-state operation. This time-varying control approach allows the system to maintain high regulation sensitivity while minimizing voltage spikes during current transitions.
Solution Approach 2:
The patent changes the operational parameters of the power device by controlling the slew rate of the gate voltage. By adjusting how quickly the gate voltage changes, the system optimizes the trade-off between transconductance utilization for regulation sensitivity and the resulting output voltage spikes during current transitions.
Data Source
AI summary
A low-dropout regulator having an output current branch being arranged between a supply line to provide a supply potential and an output node to provide a regulated output voltage. The output current branch includes an output driver to provide an output current at the output node. The output driver has a control connection to apply a control voltage to operate the output driver with a different conductivity in dependence on the control voltage. The LDO includes an input amplifier stage to provide the control voltage to the control connection of the output driver. The input amplifier stage is configured to provide the control voltage with a different slew rate in dependence on an increase or decrease of the output current.