Voltage Converter Current Steering Circuit Ringing Reduction
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Solution Overview
Problem
Low-power loss and highly efficient voltage converters, such as synchronous buck converters, face challenges in balancing efficiency and voltage ringing due to parasitic effects, requiring transistors to be rated higher than normal operation, which increases losses and reduces efficiency when trying to minimize ringing.
Innovation Solution
A voltage converter circuit with a high side transistor, a high side driver, a low side transistor, and a current steering circuit that controls the current flow during the transition of the high side transistor to the on state, initially diverting current through the current steering circuit and then increasing the current to the high side transistor as the switch node voltage rises, reducing ringing and power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the rise time of the high side transistor switch is reduced to reduce ringing, then voltage ringing is reduced, but losses increase and efficiency decreases
Solution Approach 1:
The current steering circuit performs preliminary action by controlling the gate current profile before the main switching action occurs. It pre-charges the gate capacitor in two stages: first through a controlled current path that limits di/dt, then through a higher current path that completes the gate charging. This preliminary controlled charging reduces the abrupt current changes that cause ringing while still achieving fast switching.
Solution Approach 2:
The current steering circuit dynamically adjusts the current flow to the gate based on the switching phase. During the initial phase, it limits current to reduce ringing; during the final phase, it increases current to achieve fast turn-on. This dynamic current adjustment allows the system to optimize both ringing reduction and switching speed/efficiency at different moments in the switching transition.
2Loss of energy
If the high side transistor switch is enhanced to reduce voltage-current overlap losses, then efficiency is improved, but parasitic inductance is excited with higher di/dt causing high ringing
Solution Approach 1:
The current steering circuit dynamically adjusts the gate charging current in two distinct phases. In the first phase, it provides limited current to reduce di/dt and minimize parasitic inductance excitation. In the second phase, it increases the current to achieve fast switching and reduce voltage-current overlap losses. This dynamic current profiling resolves the contradiction between fast switching and ringing reduction.
Solution Approach 2:
The invention changes the current parameter during the gate charging process. By varying the current magnitude at different stages of gate charging, it optimizes both the di/dt profile (to reduce ringing) and the switching speed (to reduce losses). The current steering circuit implements parameter changes that balance the competing requirements of efficiency and ringing suppression.
Data Source
AI summary
A voltage converter circuit includes a high side transistor, a high side driver coupled to a control input of the high side transistor, a low side transistor coupled to the high side transistor at a switch node, and a current steering circuit coupled to the control input of the high side and to the switch node. During transition of the high side transistor to an on state, a current from the high side driver initially divides between the control input of the high side transistor and the current steering circuit, and as a voltage on the switch node increases, less of the current from the high side driver flows through the current steering circuit and more of the current from the high side driver flows to the control input of the high side transistor.