SMPS Ramp Compensation for Low-ESR Load Stability
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Solution Overview
Problem
Conventional switched-mode power supplies using constant on-time (COT) control mode face stability issues due to high equivalent series resistance (ESR) of output capacitors, leading to poor response performance during load switching.
Innovation Solution
A controller for switched-mode power supplies that includes a sampling and feedback unit to obtain a first ramp signal and a ramp compensation unit to produce a second ramp signal, ensuring the difference between the two signals is lower than a predetermined value, thereby enhancing stability and response during load changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a ceramic capacitor with very lower ESR value is chosen as an output capacitor, then the chip area and cost are reduced, but the stability of the switched-mode power supply deteriorates
Solution Approach 1:
The patent introduces a ramp compensation unit as an intermediary component between the feedback loop and the control logic. This unit generates a compensation voltage based on the difference between two ramp signals, effectively mediating the stability issue caused by low-ESR ceramic capacitors without requiring high-ESR capacitors
Solution Approach 2:
The patent changes the control parameter from direct voltage feedback to a compensated voltage feedback that incorporates ramp signal differences. By modifying the feedback parameter to include dynamic compensation, the system achieves stability with low-ESR capacitors that would otherwise be unstable
2Reliability
If conventional ramp compensation method is used to calculate average current signal, then the compensation voltage can be generated, but the response performance during load switching deteriorates due to signal delay
Solution Approach 1:
The patent uses a latch circuit to capture and hold the minimum value of the first ramp signal in advance before the comparison process occurs. This preliminary action eliminates the need for continuous averaging calculations, removing the time delay associated with calculating average current signals
Solution Approach 2:
The patent extracts only the critical minimum value from the first ramp signal using a latch circuit, rather than processing the entire signal waveform through averaging calculations. This extraction approach generates compensation voltage without the time penalty of full signal processing
Data Source
AI summary
A controller in a switched-mode power supply and a method for control thereof are disclosed by the present invention. The controller provided in the present invention is used to control a power switching device in the switched-mode power supply to convert an input DC voltage into an output DC voltage. The controller includes a sampling and feedback unit and a ramp compensation unit and is configured to obtain a first ramp signal reflecting energy variation of an energy storage element and to produce a second ramp signal from the first ramp signal so that the difference between the second ramp signal and the first ramp signal is lower than a predetermined value.