Constant-Amplitude Ramp Circuit for Stable PWM Converter Response
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Solution Overview
Problem
Existing switching converter controllers face sub-optimal transient responses across different output voltages due to ramp generator amplitude variations, leading to inferior performance at higher output voltages, and require complex circuits or additional components, which are impractical for small area and low power consumption applications.
Innovation Solution
A constant amplitude ramp generator circuit that sets the ramp amplitude based on PWM timing rather than input voltage, using a current source charging a capacitor for a fixed time and discharging it through a resistor, or employing a switched capacitor circuit to maintain consistent ramp height, making it immune to process and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional ramp generator is used in switching converter controllers, then the circuit can be implemented, but the ramp amplitude varies with input and output voltages resulting in sub-optimal transient responses and inferior performance at higher output voltages
Solution Approach 1:
The patent changes the fundamental parameter determining ramp amplitude from voltage-dependent (conventional) to current-dependent (invention). By using a current source to charge the ramp capacitor, the ramp amplitude becomes independent of input and output voltage variations, ensuring consistent transient response performance across the full output voltage range from 0.6V to 5.5V.
2Reliability
If complex circuits or additional components are used to maintain constant ramp amplitude, then performance consistency can be improved, but the device area and power consumption increase
Solution Approach 1:
The patent employs a current source that automatically adjusts its operation based on the switching cycle timing, eliminating the need for external voltage sensing or complex control circuits. The current source charges the capacitor during the switching cycle and the capacitor naturally discharges through the resistor, creating a self-regulating constant amplitude ramp generator that minimizes power consumption and device area.
3Reliability
If a current source charging a capacitor for a fixed time is used, then constant ramp amplitude can be achieved, but additional circuit components are required
Solution Approach 1:
The patent merges the current source, capacitor, and resistor into an integrated ramp generation block that is directly coupled to the switching converter controller. The current source charges the capacitor during the switching cycle, and the capacitor discharges through the resistor to generate the ramp signal, combining multiple functions into a compact circuit that achieves constant amplitude without requiring separate voltage sensing or control circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides high loop crossover and superior transient performance, allowing for smaller and cheaper system designs with minimal current consumption, and maintains consistent performance across a wide range of output voltages from 0.6 to 5.5V, reducing undershoot during load transients.
Implementation Method 1
a first terminal of a capacitor is coupled to a ramp terminal and a second capacitor terminal is coupled to a return terminal
Implementation Method 2
A resistor has a first terminal coupled to the return terminal
Data Source
AI summary
In described examples of a ramp circuit, a first terminal of a capacitor is coupled to a ramp terminal and a second capacitor terminal is coupled to a return terminal. A charge source has an input terminal coupled to a supply terminal and a charge output terminal. A resistor has a first terminal coupled to the return terminal. A first switch is coupled between the ramp terminal and a second terminal of the resistor. A second switch is coupled between the charge output terminal and the ramp terminal.