AVR042: AVR Hardware Design Considerations
• Providing robust supply voltage, digital and analog.
• Connection of RESET line.
• SPI interface for In-System Programming.
• Using external crystal or ceramic resonator oscillators.
This application note has been written to provide answers to some of the questions
and problems faced when starting designs involving AVR microcontrollers. The
application note treats topics that are known to cause problems. The scope is to
provide an introduction to potential design problems rather than being an
exhaustive walk-through of how to design applications using the AVR
microcontrollers. This document is thus a collection of information from existing
Atmel AVR documents, combined with information that is not previously
It is highly recommended to read the application note AVR040 - “EMC Design
Considerations” – before initiating a new design, specially if the aim of the design is
a commercial application that needs to meet the requirements of the EMC directive
(or similar directives in countries outside Europe). The application note is available
from the AVR section of the official Atmel website http://www.atmel.com.
2 Power Supply
Two aspects should be considered when designing the power supply for the
discrete/digital elements of an AVR; ESD protection and noise emission. Both these
topics are treated in details in the AVR040 application note, and only a short
summary is included in this document.
2.1 Digital supply
Looking at the datasheet for an AVR microcontroller, one can be fooled to believe that
power supply is not critical. The device has a very wide voltage range, and draws only
a few mA supply current. But as with all digital circuits, the supply current is an
average value. The current is drawn in very short spikes on the clock edges, and if
I/O lines are switching, the spikes wil