PDM DAC Slope Compensation for SMPS Stability

Solution Overview

Problem

Switch mode power supplies (SMPS) face instability due to a changing relationship between peak and average current when the pulse width modulation (PWM) duty cycle exceeds 50%, leading to sub-harmonic oscillations, which existing analog slope compensation circuits fail to address effectively due to high costs and complexity, especially in small process geometry integrated circuits.

Innovation Solution

A pulse density modulated digital-to-analog converter (PDM DAC) with slope compensation functionality, incorporating a PDM DAC accumulator, adder, multiplexer, slope generator, and low pass filter, provides a low-cost, mixed signal integrated circuit solution that stabilizes SMPS by generating reference voltages using pulse density modulation and digital slope generation, reducing the need for expensive analog components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If analog slope compensation circuits are used to stabilize SMPS, then stability is improved, but cost and device complexity increase

Engineering Contradiction:

ImproveSMPS stabilityVSAvoidcircuit complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The patent replaces the analog slope compensation circuit with a digital implementation using a microcontroller. The microcontroller digitally generates the slope compensation signal by calculating the difference between peak and average current values and adding this to the PWM duty cycle signal. This substitution of digital processing for analog circuitry reduces device complexity, eliminates external analog components, and lowers cost while maintaining stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Stability of the object's composition

If analog slope compensation circuits are used to stabilize SMPS, then stability is improved, but manufacturing cost increases

Engineering Contradiction:

ImproveSMPS stabilityVSAvoidmanufacturing cost

Core Design Contradiction:

Stability of the object's compositionVSEase of manufacture

Solution Approach 1:

The patent replaces the analog slope compensation circuit with a digital implementation using a microcontroller. The microcontroller digitally generates the slope compensation signal by calculating the difference between peak and average current values and adding this to the PWM duty cycle signal. This substitution of digital processing for analog circuitry reduces device complexity, eliminates external analog components, and lowers cost while maintaining stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If digital implementations of PCMC are used, then device integration is improved, but slope compensation functionality becomes complex and costly

Engineering Contradiction:

Improvecircuit integrationVSAvoidslope compensation cost

Core Design Contradiction:

Device complexityVSEase of manufacture

Solution Approach 1:

The patent integrates slope compensation functionality into the existing digital PCMC microcontroller by utilizing its existing digital-to-analog converter (DAC) and pulse width modulation (PWM) capabilities. The microcontroller performs multiple functions: peak current detection, average current measurement, slope compensation calculation, and PWM generation. This multi-functional approach eliminates the need for separate slope compensation hardware, reducing cost and complexity while maintaining full functionality.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentEP2973973B1Pulse density digital-to-analog converter with slope compensation function for switch mode power supplies

Publication Date: 2019.11.27 MICROCHIP TECHNOLOGY INC

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AI summary

A slope compensation module provides slope compensation of a switched-mode power supply using current mode control. This slope compensation function may be provided by a digital slope compensation generator and a pulse density modulated digital-to- analog converter (PDM DAC) having a selectable response mode low pass filter.