LDO Current Mirror Switching for Low Dropout Quiescent Current
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Solution Overview
Problem
Conventional low dropout regulators (LDOs) experience a significant increase in quiescent current when operating in the dropout region, leading to higher operation currents even when the input voltage is near or less than the target output voltage, which is undesirable and affects the output voltage stability.
Innovation Solution
The proposed solution involves an error amplifier, a current mirror, and a comparator that compare the LDO output voltage to a resistive divider, with a control voltage generated to manage the quiescent current, using a current source at the non-inverting input of the comparator to maintain low quiescent current levels even when the input voltage is near or less than the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the input voltage becomes near or less than the target output voltage (dropout region operation), then the LDO cannot output the exact target voltage, but the quiescent current significantly increases which is undesirable
Solution Approach 1:
The patent applies dynamics by making the current mirror ratio adjustable based on operating conditions. The first and second current mirrors have different ratios that can be dynamically selected: the first current mirror has a higher ratio for normal operation, while the second current mirror has a lower ratio for dropout region operation. This dynamic adjustment allows the system to optimize quiescent current based on the input voltage level without compromising output voltage stability.
Solution Approach 2:
The patent changes the current mirror ratio parameter depending on the operating region. By switching between different current mirror ratios (first ratio for normal operation, second ratio for dropout region), the system adapts its electrical parameters to maintain low quiescent current while ensuring reliable output voltage regulation in both operating conditions.
2Adaptability or versatility
If a conventional current mirror circuit is used to maintain the desired current mirror ratio, then the input voltage must be sufficiently high, but this limits the LDO's ability to operate in the dropout region
Solution Approach 1:
The patent segments the current mirror function into two separate current mirrors: a first current mirror for normal operation with a first current mirror ratio, and a second current mirror for dropout region operation with a second current mirror ratio. This segmentation allows each current mirror to be optimized for its specific operating region, enabling accurate current mirroring in both high and low input voltage conditions.
Solution Approach 2:
The system dynamically switches between different current mirror configurations based on the input voltage level. The control circuit selects which current mirror to use, allowing the system to maintain accurate current mirror ratios across different operating conditions and extend dropout region capability without sacrificing precision.
3Use of energy by moving object
If the input voltage decreases to near or less than the target output voltage, then the feedback divided voltage is kept less than Vref, but the input current of the current mirror increases to a maximum
Solution Approach 1:
The patent changes the current mirror ratio parameter based on the operating region to prevent operation current from increasing to maximum in dropout conditions. By using a lower second current mirror ratio in the dropout region, the system maintains efficient operation current levels even when the input voltage is near or less than the output voltage, preventing the feedback-driven current increase.
Solution Approach 2:
The control circuit uses feedback from the input voltage level to determine which current mirror configuration to employ. When the input voltage drops into the dropout region, the feedback mechanism activates the second current mirror with the lower ratio, preventing excessive operation current while maintaining the necessary regulation function.
Data Source
AI summary
A Low Dropout Regulator (LDO) with Less Quiescent Current in the Dropout Region is described, including an error amplifier configured to compare a reference voltage to an LDO output voltage across a resistive divider, a current mirror configured to mirror a first output of the error amplifier to a first and second output of the current mirror, and a comparator configured to compare the LDO output voltage to a second output of the error amplifier, which has been compared to the second output of the current mirror, and configured to output a control voltage to the error amplifier, where a low quiescent current is maintained when an LDO input voltage is near or less than the LDO output voltage.