LDO Startup Overshoot Control via Dual Amplifier Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Low-dropout regulators (LDOs) experience significant overshooting during startup due to design constraints and delays in the differential amplifier, leading to uncontrolled current and power consumption issues, which existing techniques struggle to address effectively.
Innovation Solution
A low-dropout regulator design incorporating a first differential amplifier, a power transistor, and a second complementary differential amplifier, with a switching element that operates in two modes: one where the second differential amplifier is enabled during startup and another where it is switched off, allowing the first differential amplifier to produce the output voltage, thereby minimizing overshooting and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a PMOS transistor is used as power transistor with NMOS input stage differential amplifier, then power consumption is reduced and transient response is improved, but output voltage overshoots significantly at startup
Solution Approach 1:
The patent implements a dynamic switching mechanism that changes the operational mode of the differential amplifier based on startup conditions. A switching element dynamically connects or disconnects the second differential amplifier stage, transitioning the system from a two-stage configuration during startup to a single-stage configuration during normal operation, thereby adapting the system behavior to different operational phases
Solution Approach 2:
The patent applies preliminary action by enabling the second differential amplifier stage before the startup sequence begins. This preliminary configuration ensures that the power transistor gate is properly controlled from the outset, preventing the floating gate condition that causes overshoot. The switching element is pre-configured to activate this additional stage during the critical startup phase
2Device complexity
If the differential amplifier operates with floating power transistor gate at startup, then circuit simplicity is maintained, but uncontrolled current flows or output stays at ground
Solution Approach 1:
The patent introduces a switching element as an intermediary component between the differential amplifier stages and the power transistor gate. This switching element acts as a mediator that controls the connection of the second differential amplifier stage, preventing the floating gate condition without requiring fundamental changes to the basic LDO circuit structure
Solution Approach 2:
The patent segments the differential amplifier into two distinct stages: a first differential amplifier stage that operates continuously, and a second differential amplifier stage that is selectively activated during startup. This segmentation allows the system to have different operational characteristics during startup versus normal operation, solving the startup control issue while maintaining circuit simplicity
3Reliability
If a fast current limiter is designed to reduce overshoot, then output voltage stability is improved, but power consumption increases significantly
Solution Approach 1:
The patent implements a dynamic configuration where the second differential amplifier stage is only activated during the critical startup phase when overshoot is a concern. During normal operation, this stage is switched off, avoiding the continuous power consumption that would result from always-active current limiting mechanisms. The switching element enables this dynamic behavior
Data Source
AI summary
In one embodiment a low-dropout regulator comprises a first differential amplifier (Nmos1) to receive an input voltage (Vin), a power transistor (T1) coupled to the first differential input pair (Nmos1), the power transistor having an output (OUT) forming an output terminal of the low-dropout regulator to provide an output voltage (Vout) as a function of the input voltage (Vin), a second differential amplifier (Pmos1) coupled to the first differential amplifier (Nmos1), and a switching element (Mncut1, Mncut2) coupled between first and second differential amplifier (Nmos1, Pmos1), said switching element (Mncut1, Mncut2) being operated as a function of a feedback signal (Sfb) derived from the output voltage (Vout). The second differential amplifier (Pmos1) is complementary to the first differential amplifier (Nmos1). The low-dropout regulator is operated in one of two modes such that in a first mode the second differential amplifier (Pmos1) is enabled and in the second mode the first differential amplifier (Nmos1) is enabled and the second differential amplifier (Pmos1) is disabled by means of the switching element (Mncut1, Mncut2).