How to Derive More System Efficiency from Battery-Powered Designs

June 06, 2019

Christine Young  By: Christine Young
 Blogger, Maxim Integrated 

CPUs, field programmable gate arrays (FPGAs), digital signal processors (DSPs), and other processors are now handling heavy computational loads in portable electronic devices. Consumers increasingly expect their small, battery-powered electronic devices to provide long run-times between charges. This blog post highlights how dynamic power management capabilities in buck, or step-down, converters—key components of power supplies—can generate greater energy efficiency for entire systems that are powered by 1-, 2-, and 3-cell lithium-ion batteries.

Designers of compact portable devices must address challenges around high power consumption and heat dissipation. Because of this, power supplies for processors should have high voltage accuracy, high load transient performance, and high efficiency to support reliable processor performance.

In the not-too-distant past, handheld electronics required no or just one step-down converter to power their different functional blocks. A designer could use several low-dropout (LDO) linear regulators. Popular processors were typically at the 3V-3.3V range; an LDO works with reasonable efficiency using a single-cell lithium-ion battery input. As processing power demands continue rising, however, core voltages and typical I/O voltages have been dropping. LDOs are inefficient at low output voltages. In addition, they also tend to dissipate a lot of heat when operating from single- or multi-cell lithium-ion batteries.

Video game controllerVideo game controllers provide an example of a portable, battery-powered device that can benefit from buck controllers in the power supply.

In this new portable design landscape, buck converters have emerged as an answer to the efficiency puzzle. When evaluating buck converters for small consumer electronic applications, here are some capabilities to consider:

  • High conversion efficiency for maximum battery power to the load. Low quiescent current contributes to this, too, while also enabling longer standby time.
  • Skip/light load mode to reduce switching losses at low output current.
  • Voltage scaling and positioning to optimize the output voltage operating point.
  • Multi-phase support for lower input and output capacitance (multi-phase devices reduce the number of input and output capacitors). For designs based on microcontrollers, multi-phase designs deliver faster transient responses that are important for microcontroller operations.
  • Multi-channel support, where a single device can supply multiple rails.

The converter’s ability to be dynamically controlled to optimize its various parameters presents another useful feature. Consider, as an example, a system with a sensor requiring a 3.3V power rail and a Bluetooth component that requires only a 2.7V rail. The buck converter for the system will support the highest voltage requirement. However, this setup is inefficient for the lower voltage components, especially if the higher voltage component operates infrequently. Dynamic voltage scaling optimizes system efficiency by dynamically lowering the voltage of the buck converter to meet the requirements of the lower voltage components when the higher voltage component (the main sensor, in this example) is off.

Flexible Point-of-Load Regulation

Some multiphase buck converters on the market require larger inductors and more silicon area, while others don’t provide the current levels to support the latest CPUs and GPUs. Maxim offers a variety of highly efficient buck converters designed for application processors that require high current and low operating voltages:

  • For 1-cell battery-powered electronics, FPGAs, and digital signal processors (DSPs), the MAX77812 buck converter provides flexible point-of-load regulation with fast transient response and internal power sequencing.
  • The MAX77874 16A quad-phase, step-down buck regulator for multicore CPU and GPU processors is ideal for portable electronics powered by single-cell batteries.
  • The MAX77503 1.5A, 14VIN high-efficiency buck converter operates from 2- and 3-cell batteries or USB-C Power Delivery for direct conversion to point-of-load voltages.
  • The MAX8973A three-phase, step-down switching regulator is designed to meet performance and size requirements of next-generation smartphone designs.

Portable electronics continue to get smaller, while demanding more of their processors. These processors need highly efficient power supplies. This post explained how buck converters with features such as dynamic voltage scaling and low quiescent current can meet the needs. To learn more, read this white paper by Eric Pittana and Sami Nijim, “Generating Greater System Efficiency for Single- to Multi-Cell Battery-Powered Designs.”