Ramp Injection Switching in COT Regulators to Prevent DCM Group Pulsing
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Solution Overview
Problem
Constant-on-time (COT) buck regulators experience instability and reduced efficiency due to group pulsing behavior when operating in discontinuous conduction mode (DCM) with high ramp injection, leading to increased output ripples and reduced transient response.
Innovation Solution
Incorporating a ramp switch controlled by a driver to block ramp injection during tri-state in DCM, sensed by the states of the high and low-side power switches, preventing unnecessary switching and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high ramp injection is used to prevent jitter in CCM operation, then stability is improved, but group pulsing behavior occurs in DCM operation reducing efficiency and transient response
Solution Approach 1:
The ramp switch dynamically changes the state of the ramp injection circuit based on the conduction mode. In CCM, the ramp injection is enabled to prevent jitter and ensure stability. In DCM, the ramp switch turns off the ramp injection circuit to eliminate group pulsing behavior and improve efficiency. This dynamic adaptation allows the system to optimize performance for each operating mode.
Solution Approach 2:
The invention changes the parameter of ramp injection amplitude from a fixed high value to a variable value that depends on the operating mode. By using the ramp switch to control the ramp injection circuit, the system adjusts the ramp injection parameter: high amplitude in CCM for stability, and zero amplitude in DCM to prevent group pulsing and improve efficiency.
2Reliability
If high ramp injection is used to prevent jitter in CCM operation, then stability is improved, but transient response is reduced in DCM operation
Solution Approach 1:
The ramp switch enables dynamic control of the ramp injection circuit based on real-time detection of conduction mode. When transitioning from CCM to DCM, the system quickly disables the ramp injection to allow faster transient response. This dynamic adjustment eliminates the delay and oscillation associated with group pulsing behavior, improving the speed of response during transient conditions in DCM.
3Reliability
If ramp injection circuit operates continuously in DCM, then jitter is prevented, but group pulsing behavior occurs reducing efficiency
Solution Approach 1:
The invention extracts or removes the ramp injection function specifically during DCM operation by using the ramp switch to disconnect the ramp injection circuit when tri-state is detected. This selective removal of the ramp injection during DCM eliminates the harmful group pulsing behavior while maintaining it during CCM where it provides beneficial jitter prevention.
Data Source
AI summary
A switched-mode power supply, such as a constant on time regulator, is presented. The switched-mode power supply includes a high side power switch coupled to a low side power switch at a switching node. A ramp injection circuit is coupled to the switching node and a ramp switch is coupled to the ramp injection circuit are also provided. A driver is used to drive the high side power switch and the low side power switch and to control the ramp switch. The driver turns off the ramp switch when the switch-mode power supply enters a tri-state, and turns the ramp switch back on when the switch-mode power supply exists the tri-state. The tri-state occurs when the switched-mode power supply operates in a discontinuous current mode, when both the high side power switch and the low side power switch are turned off.