Introduction
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SPRAC74A–February 2017–Revised March 2017
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AM335x Low Power Design Guide
1 Introduction
The AM335x processor family features an ARM Cortex-A8 and was created with power-sensitive and cost-
sensitive applications in mind. These applications include industrial communications, IoT gateways,
renewable energy gateways, substation automation and streaming audio players. These diverse set of
applications require a processor family that provides a wide range of performance levels (ranging from
300 MHz to 1 GHz), a comprehensive integration of connectivity peripherals and key enhancements in
industrial spaces, which require 3D graphics and multiple display options.
At the end of this document, the developer will know about many of the low power features of the
AM335x, and how to optimize power consumption for their specific application. First, the hardware
considerations, when designing a schematic to take advantage of all the low power features of AM335x,
are discussed such as power management IC selection. Then, low power features in Linux are highlighted
to illustrate how software can be used to optimize runtime power even in existing designs. Finally, several
low power optimized use cases are documented with corresponding power consumption figures to
demonstrate the potential power savings.
2 Hardware Low Power Design Guidelines
When designing a system for low power, there are several special considerations to be made to ensure an
efficient final product. Concepts discussed in this section include designing a power distribution network,
I/O planning and configuration, thermal considerations, memory technology selection, and design for
measurability. This section focuses on design considerations specifically for low power design of the
AM335x processor. There are many other design decisions to make when creating a system, and for a
more complete checklist of design decisions, see the schematic checklist in the AM335x Schematic
Checklist and the AM335x Hardware Design Guide wiki pages.
2.1 Power Tree
When designing a system, begin with outlining the power requirements for the system by creating a power
tree. A power tree maps out where power comes from in the system, from an initial AC wall socket,
battery, and so forth, to how it is translated to voltages used within the system, and finally to the actual
consumers of power in a system such as a processor or peripherals such as displays and sensors. A
good power tree clearly outlines all the voltage rails and currents required and indicate the number of
voltage translations necessary to generate these voltages. Having a power tree helps the system designer
define the power supply requirements of the device.
Here are some points and places for optimization that must be addressed by a complete power tree
design.
• How many voltage translations does the power tree have? Are all strictly necessary? Minimize number
of voltage level translations to reduce conversion losses.
• How efficient are voltage regulators? Choose high efficiency regulators where it counts (high current
rails supplying processor, DDR, peripherals).
• What peripheral voltage(s) are used? Use 1.8 V I/O peripherals to minimize power consumption.
• What memory technology is being used? Is the optimum voltage being used? Sometimes there is a
trade off to be made, for example, some PMICs cannot support a dedicated 1.35 V output for DDR3L,
and many PMICs will already supply a 1.8 V rail since it is a common I/O voltage. The system designer
must weigh lower BOM cost, vs higher power consumption.
In order to determine the power requirements of the AM335x, see the Maximum Current Ratings at
AM335x Power Terminals table in the AM335x Sitara™ Processors Data Manual. This table details the
maximum current draw for each of the AM335x power domains.
2.1.1 Power Supply Selection
Although it is possible to design a discrete power supply solution, it is highly recommended to use a
Power Management IC (PMIC) as a power supply for the AM335x. PMICs offer several features that are
useful for low power design such as dynamic voltage rail adjustments, power sequencing, and easy to use
control interfaces.
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