LDO Current Control Circuit for Autonomous Capacitor Detection
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Solution Overview
Problem
Conventional methods for detecting an external output capacitor in low drop-out regulators (LDOs) require additional circuitry and dedicated detection timeslots, making them inefficient and disrupting LDO operation.
Innovation Solution
A circuit with a current control circuit that enables autonomous external capacitor detection and short circuit protection, allowing for automatic configuration and current limitation, using a power/sense structure and current-control differential amplifier to determine capacitor presence without external assistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional detection methods using ADC and state machine are used, then capacitor presence can be detected, but device complexity increases and LDO operation is disrupted
Solution Approach 1:
The patent combines the capacitor detection function with the existing short-circuit protection (SCP) current sense structure. The SCP differential amplifier and sense transistor are reused for dual purposes: traditional short-circuit protection and external capacitor detection. This merging eliminates the need for separate ADC and state machine circuitry, reducing device complexity while maintaining detection accuracy.
Solution Approach 2:
The current sense structure originally designed for short-circuit protection is made multi-functional by enabling it to perform both SCP and capacitor detection operations. The same hardware resources (sense transistor, differential amplifier, reference current source) serve multiple functions, eliminating dedicated detection timeslots and allowing continuous LDO operation.
2Measurement precision
If conventional detection methods with dedicated timeslots are used, then capacitor detection is achieved, but productivity decreases due to operational interruptions
Solution Approach 1:
The patent enables continuous LDO operation by eliminating dedicated detection timeslots. The reused SCP current sense structure operates continuously without interrupting LDO functionality, allowing the regulator to maintain output voltage and supply current uninterrupted while simultaneously performing capacitor detection.
Solution Approach 2:
By merging capacitor detection with the continuously operating SCP function, the patent eliminates the need to pause LDO operation for detection. The same hardware performs both functions simultaneously, ensuring uninterrupted power supply and maintaining productivity.
3Adaptability or versatility
If external capacitor detection is performed with additional circuitry, then detection capability is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent merges capacitor detection capability with the existing SCP current sense structure, eliminating the need for additional external circuitry. The detection function is achieved by reusing components already present in the LDO (sense transistor, differential amplifier, reference current source), simplifying manufacturing by reducing component count and assembly complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient and reliable detection of external capacitors during startup, allowing continuous LDO operation without dedicated detection timeslots and providing automatic short circuit protection, enhancing operational efficiency and reliability.
Implementation Method 1
Power MOS transistor 110 uses an electric field to control the shape and, hence, conductivity across the power MOS transistor's source and drain terminals
Implementation Method 2
its drain connected to a current mirror 155 (which is connected also to a current source 160)
Implementation Method 3
an SCP differential amplifier 170 that compares a potential difference V determined by the product of Rref with a difference between the current flowing through small MOS transistor 150 and a reference current, Iref
Data Source
AI summary
A circuit including a low drop-out regulator (LDO) has a current control loop configured and connected to detect whether an external capacitor is connected to the output of the LDO. The current control loop includes a differential amplifier, a current source capable to output different reference currents and a small MOS transistor. The circuit may be operated in an output capacitor detection mode when started and in a regulated voltage source mode otherwise. In the output capacitor detection mode, the small MOS transistor is driven by the differential amplifier and drives the LDO's power MOS transistor depending on a difference between a current through the small MOS transistor and the reference current output by the current source. Components of the current control loop may be used during regulated voltage source mode for short circuit protection.