LDO Startup Current Limiting Across LDO and Bypass Modes
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Solution Overview
Problem
Low dropout (LDO) regulators experience high inrush currents during startup in both LDO and Bypass modes, which are undesirable and can lead to reliability issues and increased power consumption.
Innovation Solution
The implementation of a current limit control loop with comparators that sense the current flowing through the p-channel MOSFET pass transistor, using a current limit control loop and comparators to manage the gate voltage and output voltage signals, thereby limiting the startup current in both LDO and Bypass modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional LDO regulator is used, then voltage regulation is provided, but high startup inrush current occurs in both LDO and Bypass modes
Solution Approach 1:
The patent segments the current path control by introducing separate control mechanisms for LDO mode and Bypass mode. A mode selection circuit divides the operation into two distinct current paths, with independent current limiting for each mode, thereby resolving the inrush current issue without requiring complete redesign of the entire regulator circuit.
Solution Approach 2:
The patent implements preliminary action by pre-charging the output capacitor through a controlled current path before the main power switch is fully activated. The mode selection circuit activates a preliminary current limiting path that charges the output capacitor at a controlled rate, preventing the sudden inrush current that would occur without this preparatory step.
2Reliability
If startup inrush current is limited using conventional methods, then inrush current is reduced, but silicon area and power consumption increase
Solution Approach 1:
The patent employs dynamic resistance control where the current limiting resistance is not fixed but changes based on the operating mode and startup phase. The mode selection circuit dynamically switches between different resistance values optimized for LDO mode and Bypass mode, achieving effective inrush current limiting while minimizing power loss during normal operation.
Solution Approach 2:
The patent changes the resistance parameter dynamically based on operating conditions. By using voltage-dependent or current-dependent resistors whose resistance values change with the startup phase and operating mode, the circuit achieves inrush current limiting without requiring large fixed resistors that would consume excessive power during normal operation.
Data Source
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AI summary
A low dropout (LDO) device with improved limitation of the startup inrush current in the LDO and bypass mode of operation. A low dropout device with limiting startup inrush current, the device comprising of a power source, an error amplifier, a pass transistor, a feedback network, and a current limit control whose input is electrically connected to said pass transistor and the electrical output of said error amplifier and whose output is providing a current limit during startup. The low dropout device further comprises a LDO mode current control limit comparator wherein said LDO mode current control limit comparator input comprises of a power source, and output of said pass transistor. The low dropout device further comprises a Bypass mode current control limit comparator wherein said Bypass mode current limit comparator input comprises of a first input voltage of said error amplifier, and a second input voltage from said error amplifier.