Voltage Regulator Startup Control for Prioritized External Pass Transistor
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Solution Overview
Problem
Low dropout (LDO) voltage regulators face challenges in determining whether an external pass device is present at startup, which affects thermal management and current distribution between internal and external pass devices.
Innovation Solution
A voltage regulator design that employs two concurrent control loops, one for an external pass transistor and another for an internal pass transistor, with a prioritized first control loop to ensure safe startup and thermal management by prioritizing the external pass transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an external pass device is used to supply high current to the load, then heat dissipation outside the integrated circuit increases, but the presence of the external pass device is unknown at startup causing control uncertainty
Solution Approach 1:
The patent segments the control system into two independent control loops: a first control loop for the external pass device and a second control loop for the internal pass device. Each loop operates autonomously with its own error amplifier and feedback path, allowing the system to manage control uncertainty by treating each pass device as a separate controllable entity rather than a unified system.
Solution Approach 2:
The patent changes the feedback voltage parameter by providing a first feedback voltage to the first control loop and a second feedback voltage to the second control loop. This parameter differentiation enables each control loop to independently regulate its respective pass device, resolving the control uncertainty at startup by allowing both loops to operate with appropriate feedback signals.
2Productivity
If both control loops run concurrently during startup, then current distribution between internal and external pass devices is needed, but prioritization is required to reduce current through the internal pass transistor
Solution Approach 1:
The patent implements feedback mechanisms in both control loops where error amplifiers continuously monitor the feedback voltages and adjust the control signals accordingly. The first error amplifier receives first feedback voltage and the second error amplifier receives second feedback voltage, enabling dynamic current distribution that prioritizes the external pass device while reducing thermal stress on the internal pass transistor through closed-loop control.
Solution Approach 2:
The patent enables dynamic operation of both control loops during startup, allowing the system to adaptively distribute current between the internal and external pass devices. The control loops can dynamically adjust their operation based on load conditions and thermal requirements, with the capability to prioritize the external pass device when thermal management is critical.
Data Source
Figure 1~2
Figure 3
Figure 4A~4C
AI summary
A voltage regulator utilizes an external pass transistor coupled between a supply voltage node and a regulated node. The voltage regulator includes an internal pass transistor that is coupled between the supply voltage node and the regulated node. A two-tap voltage divider between the regulated node and a ground node provides two feedback voltages. A first control loop that controls the external pass transistor receives the first feedback voltage and a second control loop that controls the internal pass transistor receives the second feedback voltage. At startup the control loops run concurrently but the first control loop is prioritized to reduce load current provided by the internal pass transistor at the end of startup. The voltage difference between the first and second feedback voltages ensures prioritization of the first control loop and the external pass transistor supplies most or all of the load current.