LDO Regulator Pass-Through Switching for Low Dropout Current
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Solution Overview
Problem
Conventional low-dropout (LDO) regulators for battery-operated devices experience a significant increase in quiescent current when they enter the drop-out zone of operation, leading to rapid battery discharge, as they struggle to maintain regulation when the input voltage approaches the output voltage.
Innovation Solution
The proposed solution involves a low quiescent current LDO regulator that tracks both input and output voltages and transitions into a pass-through mode before entering the drop-out zone, using a pair of transistors and amplifiers to compare voltages and control the pass device, thereby reducing the quiescent current by shorting the input voltage node to the output node when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LDO regulator operates in conventional mode, then voltage regulation is maintained, but quiescent current increases significantly when entering drop-out zone
Solution Approach 1:
The LDO regulator dynamically switches between conventional regulation mode and pass-through mode based on the voltage difference between input and output. When Vin-Vout exceeds a threshold, the regulator operates in pass-through mode with minimal quiescent current; when the difference is smaller, it transitions to conventional regulation mode to maintain proper voltage control.
Solution Approach 2:
The regulator changes its operational parameters by switching the state of the pass transistor. In pass-through mode, the transistor is fully on with gate-source voltage maximized, minimizing resistance and quiescent current. In regulation mode, the transistor operates in its linear region with controlled gate voltage to maintain output voltage stability.
2Use of energy by moving object
If the LDO regulator enters drop-out zone, then quiescent current is reduced, but voltage regulation is lost
Solution Approach 1:
The regulator proactively transitions to pass-through mode before entering the drop-out zone by monitoring the voltage difference between input and output. This preliminary action prevents the drop-out condition from occurring, maintaining both low quiescent current and proper voltage regulation simultaneously.
Solution Approach 2:
The regulator uses feedback from the output voltage and input voltage sensing to continuously monitor the voltage difference. This feedback mechanism controls the pass transistor gate voltage, ensuring the regulator transitions between modes at the appropriate moment to maintain regulation while minimizing current consumption.
3Use of energy by moving object
If the LDO regulator uses pass-through mode, then quiescent current is minimized, but control over output voltage is reduced
Solution Approach 1:
The regulator dynamically adjusts its control mechanism based on operating conditions. In pass-through mode, the control is simplified to maintaining the transistor in full conduction state. In regulation mode, the full feedback control mechanism is activated to precisely control the output voltage, providing the appropriate level of control for each operating condition.
Data Source
AI summary
A low-dropout (LDO) regulator and an associated method and apparatus are described. The LDO regulator generally includes a first transistor coupled between an input voltage node and an output voltage node of the LDO regulator. The LDO regulator further includes a first amplifier having an output coupled to a gate of the first transistor, wherein a feedback path couples the output voltage node to an input of the first amplifier. The LDO regulator further includes a second amplifier having an output coupled to an enable input of the first amplifier, wherein a voltage-sensing path couples the input voltage node to an input of the second amplifier. The LDO regulator further includes and a second transistor coupled between the gate of the first transistor and a reference potential node, the output of the second amplifier being coupled to a gate of the second transistor.