Ultra-low I_Q COT Controlled Synchronous Buck Converter

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Abstract

With the proliferation of portable, wearable and IOT devices, the demand for ultra-low energy consumption in idle mode is a major requirement to prolong battery life and reduce maintenance cost. For these applications, systems spend most of the time in standby or idle mode. Minimizing quiescent current (I_Q) is a key factor in reducing power consumption and managing battery life for many applications. Low quiescent current means higher efficiency at ultra-light load, which results in longer battery life. Ways to achieve low-I_Q technologies without compromising system performance based on M3TEK’s proprietary COT control architecture are discussed. Methods to measure light load efficiency for ultra-low I_Q system are also explained for M3TEK MT8351 family ultra-low I_Q devices.

Table of Contents

1. Introduction
2. Low I_Q Design Optimization
3. Accurate Efficiency Measurement for Low I_Q Device
4. Conclusion
5. References

Introduction

The world is becoming battery powered than ever. With the proliferation of portable, wearable and IOT devices, a new class of applications is emerging. The main power source for these applications is either battery or harvested energy from the environment, and most of system’s operating life is spent in idle or standby mode. To prolong the battery life and reduce maintenance cost, the system must work with very low energy consumption during idle mode. At the same time, power management systems need to respond to fast load change and provide tightly regulated voltage rail for sensitive circuit like sensors and wireless communication devices.

To achieve these goals, low I_Q is an important design target of DC-DC converters, which can improve the standby time of the device and energy saving. Therefore, I_Q in standby or sleep mode is a limited factor for battery life or other devices. DC-DC devices need to adopt efficient power conversion technology, optimized control architecture and rationalize power management module to achieve low I_Q.

Low I_Q Design Optimization

For a DC-DC converter, I_Q is different from input current in no load and is sometimes misunderstood by engineers. I_Q is defined as the current drawn by the DC-DC converter under no load and non-switching mode with device enabled and output voltage in regulation. “No load” indicates no current flows into output. “Non-switching” means both high-side and low-side power switches are turned off. I_Q usually comes from VIN, VOUT or some other pins which defined in datasheet specification for an IC.

Buck converter draws I_Q only from VIN as specified in a buck converter MT8123 datasheet from M3TEK. For boost or buck-boost converter, I_Q is drawn from VIN and VOUT such as specified for boost converter MT5070 from M3TEK.