AM335x Hardware Design Guide


 * The TMDXEVM3358 EVM is always a good source from which to start building a reference design for these devices. The technical documentation for the EVM is available.


 * The links at the TI website below provide block diagrams, application notes, tools, software, design considerations, and other related information for various products under category "Related End Equipments".
 * AM335x Product Folder


 * Select from a list of complementary devices to attach to AM335x device in your system:
 * Power Management Devices refer link

Selecting the Boot Mode
The block diagram should also indicate which interface will be used for booting this device.


 * These devices contain an on-chip ROM Bootloader:
 * The boot config pins are sampled at power-on-reset
 * Sets up system for boot depending on boot configuration selected
 * Depending on boot mode, copies image to internal RAM and then executes it
 * Maximum size of the boot image is 128KBytes
 * The following boot modes are supported:
 * NOR Flash boot
 * NAND Flash boot
 * SPI boot
 * SD/MMC boot
 * EMAC boot
 * UART boot
 * USB boot (like an ethernet card, not as mass storage)
 * If the first boot source fails to boot, the ROM will move on to the next one in the sequence. Keep in mind that some boot sources take some time to timeout if that boot source isn't available.
 * Read AM335x Technical Reference Manual Initialization Chapter to understand details on different boot modes


 * Key Boot Considerations:
 * It is recommended to include population options for other boot modes to aid in development
 * Boot pins have other functions after reset. Make sure your board design takes this into account when choosing pullup/down resistors for the boot pins.

Confirming Pin Multiplexing Compatibility
The AM335x device contains many peripheral interfaces. In order to reduce package costs while maintaining maximum functionality, many Approximately half of the AM335x terminals can multiplex up to eight signal functions. Although there are many combinations of pin-multiplexing that are possible, only a certain number of sets, called IO sets, are valid due to timing limitations. These valid IO sets were carefully chosen to provide many possible application scenarios for the user.

Texas Instruments has developed a Windows application called Pin Mux Utility that helps a system designer select the appropriate pin-multiplexing configuration for their AM335x based product design. This tool provides a way to select valid IO Sets of specific peripheral interfaces to insure the pin-multiplexing configuration selected for a design only uses valid IO Sets supported by AM335x.


 * Pin Mux Utility

Confirming Electrical and Timing Compatibility
A key step in the hardware design before beginning schematic capture is to confirm both DC and AC electrical compatibility between this device and the other ICs connected to it.


 * The device datasheet has important information with regards to timing and electrical characteristics.
 * For High Speed Interfaces you can run IBIS simulations using IBIS models provided for AM335x ZCE and ZCZ package to confirm signal Integrity.
 * ZCE Package IBIS
 * ZCZ Package IBIS


 * Using IBIS Models for Timing Analysis


 * Note: TI provides PCB layout specifications for the following interfaces, eliminating the need to perform electrical analysis:
 * lpDDR/DDR2/DDR3

Designing the Power Subsystem
Once the block diagram has been validated for pin multiplexing, electrical, and timing compatibility, the power sub-system can be designed. See the below resources on estimating power consumption and designing a matching power subsystem.


 * AM335x Power Consumption Summary: The AM335x Power Numbers discusses the power consumption for common system application usage scenarios for the AM335x ARM® Cortex™-A8 Microprocessors (MPUs). Power consumption is highly dependent on the individual user’s application; however, this document focuses on providing several AM335x application-usage case scenarios and the environment settings that were used to perform such power measurements.
 * AM335x Power Estimation Tool:   The Power Estimation Tool (PET) provides users the ability to gain insight in to the power consumption of select Sitara processors. The tool includes the ability for the user to choose multiple application scenarios and understand the power consumption as well as how advanced power saving techniques can be applied to further reduce overall power consumption.
 * AM335x Power Solution




 * TPS65217 User’s Guide for AM335x Processors (SLVU551)
 * TPS65910A User's Guide For AM335x Processors (SWCU093)
 * Powering the AM335x With the TPS650250 (SLVU731)

Designing the Clocking Subsystem
In addition to the power subsystem, the clocking subsystem needs to be designed to provide appropriate clocks to all ICs in the system. These clocks can be created by pairing crystals with internal oscillators within the system ICs, or they can be created by a separate clock generator. See the below information on designing the clocking subsystem for your design.


 * Key Considerations:
 * The device operation requires a 32k optional crystal and HF crystal with either 19.2,24,25,26 MHz reference clock for operation.
 * A 32.768-kHz clock input is an optional for the RTC.
 * For more details, please refer to the Clocking sections of the device datasheet and TRM.

Floorplanning the PCB
Before beginning schematic capture, it is recommended to floorplan the system PCB to determine the interconnect distances between the various system ICs.

Creating the Schematics
At this point in the design, it is time to start capturing the schematics. See the below collection of information to aid you in creating the schematics.


 * Key Considerations:
 * SDRAM (and other) output clocks are internally looped back
 * Don’t forget to install a JTAG connection
 * JTAG: Make sure to use the RTCK pin


 * It is often helpful to refer to example schematics throughout the schematic capture process: [TBD]
 * Make sure to use the canned schematics in the datasheet for the following interfaces:
 * lpDDR/DDR2/3
 * For detailed information on USB board design, see the USB 2.0 Board Design and Layout Guidelines application report SPRAAR7
 * During and after schematic capture, check your design against the schematic checklist:
 * Schematic Checklist
 * Plan to have an internal schematic review to go through the schematic checklist and inspect other key areas of the schematic to look for inaccuracies, missing net connections, etc.

Below are Symbols, Footprints, and Simulation Models to aid in the design of the device placement and interconnects:


 * OrCad Symbols
 * Altium Symbols
 * Allegro footprints
 * Pin Names and Numbers
 * AM335x: Available in Data Sheet in


 * BSDL Simulation Model


 * IBIS Simulation Models:


 * General hardware design information:BGA PCB Design
 * For selecting and placing decoupling capacitors in a BGA design:
 * Decoupling (Bypass) Capacitor Selection and Placement for BGAs

Laying out the PCB
After completing schematic capture, see the below information on laying out the PCB:


 * It is often helpful to refer to an example layout when designing a custom PCB: [TBD EVM Layout]
 * Make sure to follow the Layout Specifications for the following Critical Interfaces:
 * DDR2 - See Datasheet
 * mDDR/DDR3 - See Datasheet


 * Plan to have an internal PCB layout review with your design team to verify that net connection traces and the power distribution network were created correctly.


 * General Information Articles:
 * Understanding TI's PCB Routing Rule-Based DDR Timing Specification
 * BGA/PCB Design for BGAs
 * Decoupling Capacitor Selection and Placement for BGAs

Board Bringup/Diagnostic
Once your custom PCB has been produced and assembled, refer to the below information on bringing-up and debugging the system.


 * AM335x Board Bringup Tips
 * AM335x EMIF Configuration Tips
 * Overview of Debug and Trace Tools
 * In these device platforms, other processors and accelerators are often treated as a black-box and most of the development and debugging is done on the ARM Cortex-A8 side.
 * Code Composer Studio
 * Using BSDL to validate AM335x based board
 * You can use AM335x BSDL files to validate the connectivity on board build.