Semiconductor Integrated Circuit Rush Current Control
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Solution Overview
Problem
Existing semiconductor integrated circuits face challenges in precisely controlling rush currents during power-on, leading to excessive primary and secondary rush currents, which cause temporary drops in external source voltage, affect internal logic circuit startup times, and stress internal power supply wiring, potentially leading to reliability issues and electromigration problems.
Innovation Solution
A semiconductor integrated circuit design that includes a power switch circuit with a start-up circuit and control circuit, which controls the output transistor to maintain a constant increment in output current during the initial power-on period, and a regulator that detects and adjusts the internal source voltage to maintain it within a predetermined limit, thereby controlling both primary and secondary rush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the limiting current value by the current mirrors is set at a small value, then the primary rush current can be reduced, but it will take longer time to charge initially the load capacitance of the internal circuit
Solution Approach 1:
The patent applies dynamics by making the current limiting value time-dependent. During the initial power-on period, the start-up circuit sets a first limiting current value to charge the load capacitance. After this period expires, the circuit switches to a second limiting current value for normal operation. This dynamic adjustment resolves the contradiction by allowing high current only when necessary for charging, then reducing it to minimize rush current effects.
Solution Approach 2:
The start-up circuit performs preliminary action by pre-charging the load capacitance with a controlled current before the stabilizing power circuit begins normal operation. This preliminary charging phase uses a dedicated current path through the start-up circuit, separating the charging function from the normal power regulation function, thereby allowing optimized current values for each phase.
2Productivity
If a large value is set for the limiting current value by the current mirror, then the time required to initially charge the load capacitance of the internal circuit will be shorter, but the primary rush current will increase
Solution Approach 1:
The circuit dynamically switches between two current limiting modes: a higher first limiting current value during the initial charging period to achieve fast charging, and a lower second limiting current value during normal operation to reduce rush current. This temporal separation allows the system to achieve both fast charging and low rush current.
Solution Approach 2:
The patent segments the power-on process into two distinct phases: an initial charging phase handled by the start-up circuit with its own current limiting, and a normal operation phase handled by the stabilizing power circuit. This segmentation allows each phase to be optimized independently for its specific function.
3Reliability
If the time constant period of the start-up circuit is extended, then the primary rush current can be controlled longer, but the secondary rush current may increase due to voltage differences
Solution Approach 1:
The stabilizing power circuit uses feedback control to detect the internal source voltage and adjust the output current accordingly. When the start-up circuit finishes charging and the stabilizing circuit takes over, the feedback mechanism ensures a smooth transition by matching the output voltage and current, thereby minimizing secondary rush current even though the start-up period is extended.
Solution Approach 2:
The stabilizing power circuit acts as an intermediary that smoothly takes over from the start-up circuit. It mediates the transition by gradually adjusting its output to match the charged voltage level, preventing abrupt current changes that would cause secondary rush current.
Data Source
AI summary
In order to set with a high precision the value of rush current flowing in the power switch circuit at the time of turning “on” the power, the internal circuit Int_Cir of the LSI is supplied with the internal source voltage Vint from the output transistor MP1 of the regulator VReg of the power switch circuit PSWC. The power switch circuit PSWC includes a control circuit CNTRLR and a start-up circuit STC. During the initial period Tint following the turning “on” of the power supply, the start-up circuit STC controls the output transistor MP1 and reduces the primary rush current so that the output current Isup of the output transistor MP1 may represent an approximately constant increment as the time passes. The difference ΔV between the internal current voltage due to the charge of load capacitance C with the output current Isup controlled by the start-up circuit STC and the current voltage Vint from the regulator VReg is set within the predetermined limit to reduce the secondary rush current.