Atmel AT01607 Installation and operating instructions

APPLICATION NOTE

Atmel AT01607: XMEGA C Schematic Checklist

8-bit Atmel Microcontrollers

Features

•Power supplies

•Reset circuit

•Clocks and crystal oscillators

•PDI

•USB

Introduction

This application note describes a common checklist which should be used when

starting and reviewing the schematics for an Atmel®AVR®XMEGA®C design.

8466A−AVR−06/2013

Atmel AT01607: XMEGA C Schematic ChecklistAtmel AT01607: XMEGA C Schematic Checklist

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8466A−AVR−06/2013

Table of Contents

1. Power supplies...................................................................................3

1.1 Power supply connections ................................................................................3

1.2 External analog reference connections.............................................................4

2. External reset circuit...........................................................................4

3. Clocks and crystal oscillators .............................................................5

3.1 External clock source........................................................................................5

3.2 Crystal oscillator................................................................................................6

3.3 Real-time oscillator............................................................................................6

4. PDI interface......................................................................................8

5. USB interface.....................................................................................9

6. Suggested reading...........................................................................10

6.1 Datasheets and manual..................................................................................10

7. Revision History...............................................................................11

Atmel AT01607: XMEGA C Schematic ChecklistAtmel AT01607: XMEGA C Schematic Checklist

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1. Power supplies

1.1 Power supply connections

All power supply pins of the device must be connected to the microcontroller supply.

Both VCC (digital) and AVCC (analog) must be connected to the same microcontroller positive supply, thus ensuring that

they both share an identical supply profile. Likewise both ground pins must be connected to the same microcontroller

ground reference supply.

Figure 1-1. Power supply schematic.

10μF

GND

AVCC

AGND

Close to device

POWER

SUPPLY

10μH100nF

VCC

100nF

10μF

Ferrite

Bead

Close to power

supply Close to device Close to device

Table 1-1. Power supply checklist.

Signal name Recommended pin connection Description

VCC 1.6V to 3.6V

Decoupling/filtering capacitors 100nF (1)(2) and 10µF (1)

Decoupling/filtering inductor 10µH (1)(3) Digital supply voltage

AVCC 1.6V to 3.6V

Decoupling/filtering capacitors 100nF (1)(2) and 10µF (1)

Ferrite bead (4) prevents the VCC noise interfering the AVCC Analog supply voltage

GND Ground

Notes: 1. These values are given only as a typical example (that is, ceramic capacitors: 100nF, SMD 0402, X7R,

16V and 10µF, SMD1206, X5R, 6.3V) (that is, inductor: 10µH, 1.2A).

2. Decoupling capacitor should be placed close to the device for each supply pin pair in the signal group, low

ESR caps should be used for better decoupling.

3. Wire wound inductor should be added between the external power and the VCC for power filtering.

4. Ferrite bead has better filtering performance than the common inductor at high frequency. It can be added

between VCC and AVCC for preventing digital noise from entering the analog power. The BEAD should

provide enough impedance (for example, 220Ω at 100MHz, rated current 200mA, that is, Murata

BLM15BB221SN1D) for separating the digital power to the analog power.

Atmel AT01607: XMEGA C Schematic ChecklistAtmel AT01607: XMEGA C Schematic Checklist

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1.2 External analog reference connections

Atmel AVR XMEGA C proposes one ADC using internal references or an external analog reference (AREFA on

PORTA).

The following schematic checklist is only recommended if the design is using the external analog reference. If the

internal reference is used, the circuit is not necessary.

Figure 1-2. External VREF schematic.

EXTERNAL

REFERENCE 1 4.7μF100nF

Close to device

AGND

AREFA

Close to power

supply

Table 1-2. External analog reference checklist.

Signal name Recommended pin connection Description

AREFA 1.0V to AVCC-0.6V for ADC

Decoupling/filtering capacitors 100nF (1)(2) and 4.7µF (1) External reference from AREF pin

on PORT A

GND Ground

Notes: 1. These values are given only as a typical example.

2. Decoupling capacitor should be placed close to the device.

2. External reset circuit

The external reset circuit is connected to /RESET pin only if the external reset function is used.

Figure 2-1. External reset circuit example schematic.

RESET

10 kΩ

VCC

Reset

Switch

100 Ω

100nF

Atmel AT01607: XMEGA C Schematic ChecklistAtmel AT01607: XMEGA C Schematic Checklist

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Table 2-1. Reset circuit checklist.

Signal name Recommended pin connection Description

______

RESET

Reset low level threshold voltage

VCC = 2.7 - 3.6V: Below 0.45 × VCC

VCC = 1.6 - 2.7V: Below 0.42 × VCC (VCC = 2.7V included) Reset pin

Notes: The pull-up resistor makes sure that reset does not go low unintended. When the PDI programming and

debugging is used, the reset line is used as clock. The reset pull-up should be 10kΩ or weaker, or be

removed.

The pull-down resistor prevents from overvoltage on the RESET pin when the switch is pressed.

Any reset capacitors should be removed if PDI programming and debugging is used. Other external reset

sources should be disconnected

3. Clocks and crystal oscillators

3.1 External clock source

Figure 3-1. External clock source example schematic.

XTAL2

XTAL1

External Clock

N.C.

Table 3-1. External clock source checklist.

Signal name Recommended pin connection Description

XTAL1 XTAL1 is used as input for an external clock signal Input for inverting oscillator pin 1

XTAL2 Can be left unconnected or used as GPIO

Atmel AT01607: XMEGA C Schematic ChecklistAtmel AT01607: XMEGA C Schematic Checklist

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3.2 Crystal oscillator

Figure 3-2. Crystal oscillator example schematic.

Up to

16 MHz

15pF

XTAL2

XTAL1

Table 3-2. Crystal oscillator checklist.

Signal name Recommended pin connection Description

XTAL1 Load capacitor 15pF

(1)(2)

External crystal between 0.4MHz to 16MHz

XTAL2 Load capacitor 15pF (1)(2)

Notes: 1. These values are given only as a typical example. Please refer to the crystal datasheet to determine the

capacitor value for the crystal used or refer to the application note “AVR1003: Using the XMEGA Clock

System”.

2. Load capacitors should be placed close to the device and crystal pins.

3.3 Real-time oscillator

The low-frequency crystal oscillator is optimized for use with a 32.768kHz watch crystal. When selecting crystals, load

capacitance and crystal’s equivalent series resistance, ESR must be taken into consideration. Both values are specified

by the crystal vendor.

The Atmel AVR XMEGA C oscillator is optimized for very low power consumption, and thus when selecting crystals, see

Table 3-3 for maximum ESR recommendations on 9pF and 12.5pF crystals.

Table 3-3. Maximum ESR recommendation for 32.768kHz watch crystal.

Crystal CL [pF] Maximum ESR [kΩ]

(1)

9.0 65

12.5 30

Notes: 1. Maximum ESR is typical value based on characterization.

The low-frequency crystal oscillator provides an internal load capacitance of typical 3.0pF. Crystals with recommended

3.0pF load capacitance can be without external capacitors as shown in Figure 3-3.

Atmel AT01607: XMEGA C Schematic ChecklistAtmel AT01607: XMEGA C Schematic Checklist

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Figure 3-3. Real-time oscillator without load capacitor.

32.768kHz

TOSC1

TOSC2

Crystals specifying load capacitance (CL) higher than 3.0pF, require external capacitors applied as described in Figure

3-4.

Figure 3-4. Real-time oscillator with load capacitor.

32.768kHz

18pF

TOSC1

TOSC2

To find suitable load capacitance for a 32.768kHz crystal, please consult the crystal datasheet.

Table 3-4. External real-time oscillator checklist.

Signal name Recommended pin connection Description

TOSC1 Load capacitor 18pF

(1)(2)

Timer oscillator pin 1

TOSC2 Load capacitor 18pF

(1)(2)

Timer oscillator pin 2

Notes: 1. These values are given only as a typical example. Please refer to the crystal datasheet to determine the

capacitor value for the crystal used or refer to the application notes “AVR1003: Using the XMEGA Clock

System” and “AVR4100: Selecting and testing 32kHz crystal oscillators for Atmel AVR microcontrollers”.

2. Load capacitors should be placed close to the crystal, GND and device oscillator pins.

Atmel AT01607: XMEGA C Schematic ChecklistAtmel AT01607: XMEGA C Schematic Checklist

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4. PDI interface

Figure 4-1. PDI interface example schematic.

PDI_DATA

RESET

VCC

10 kΩ

DATA

GND

N.C.

VCC

CLK

N.C.

2x3 header

PDI_CLK

The connector pinout that is shown in Figure 4-1 mates with Atmel tools like the Atmel AVR JTAGICE 3 and Atmel AVR

ONE!

Table 4-1. PDI port interface checklist.

Signal name Recommended pin connection Description

PDI_CLK

This pull-up resistor makes sure that reset does not go low

unintended. When the PDI programming and debugging is used,

the reset line is used as clock. The reset pull-up should be 10kΩ

or weaker, or be removed.

Any reset capacitors should be removed if PDI programming

and debugging is used. Other external reset sources should be

disconnected.

PDI clock input / reset pin

PDI_DATA PDI_DATA: PDI data input /

output

Atmel AT01607: XMEGA C Schematic ChecklistAtmel AT01607: XMEGA C Schematic Checklist

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5. USB interface

The impedance of the USB differential data line pair is 90Ωto each other and 45Ωto ground. The termination of the line

is included within the Atmel AVR XMEGA C device as serial resistors. To ensure proper signal integrity, the two D+/D-

signals must be closely routed on the PCB (Refer to “AVR1017: XMEGA - USB Hardware Design Recommendations”

application note).

Figure 5-1. Low-cost USB interface example schematic.

VBUS

USB

Connector

VBUS

D+

D-

GND

Shield

GND (Board)

USB_D+

USB_D-

USB

Differential

Data Line Pair

Figure 5-2. Protected USB interface example schematic.

4.5nF

1MΩ

VBUS

USB

Connector

VBUS

D+

D-

GND

Shield

USB Transient

protection

RC Filter

(GND/Shield

Connection) GND (Board)

USB_D+

USB_D-

USB

Differential

Data Line Pair

Atmel AT01607: XMEGA C Schematic ChecklistAtmel AT01607: XMEGA C Schematic Checklist

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Table 5-1. USB interface checklist.

Signal

name Recommended pin connection Description

D+ • The impedance of the pair should be matched on the

PCB to minimize reflections

• USB differential tracks should be routed with the

same characteristics (length, width, number of vias, etc.)

• Signals should be routed as parallel as possible, with

a minimum number of angles and vias

USB full speed / low speed positive

data upstream pin

D- USB full speed / low speed negative

data upstream pin

6. Suggested reading

6.1 Datasheets and manual

The datasheet and the manual contain block diagrams of the peripherals and details about implementing firmware for

the device. The datasheet and the manual are available on http://www.atmel.com/AVR in the Datasheets & Manuals

section.

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