10

8393CS-MCU Wireless-09/14

ATmega256/128/64RFR2

Capacitors should be placed as close as possible to the pins and should have a low-

resistance and low-inductance connection to ground to achieve the best performance.

The crystal (XTAL), the two load capacitors (CX1, CX2), and the internal circuitry

connected to pins XTAL1 and XTAL2 form the 16MHz crystal oscillator for the 2.4GHz

transceiver. To achieve the best accuracy and stability of the reference frequency, large

parasitic capacitances must be avoided. Crystal lines should be routed as short as

possible and not in proximity of digital I/O signals. This is especially required for the

High Data Rate Modes.

The 32.768 kHz crystal connected to the internal low power (sub 1µA) crystal oscillator

provides a stable time reference for all low power modes including 32 Bit IEEE 802.15.4

Total shunt capacitance including CX3, CX4 should not exceed 15pF across both pins.

The very low supply current of the oscillator requires careful layout of the PCB and any

leakage path must be avoided.

Crosstalk and radiation from switching digital signals to the crystal pins or the RF pins

can degrade the system performance. The programming of minimum drive strength

Table 4-1. Bill of Materials (BoM)

Designator

Description

Value

Manufacturer

Part Number

Comment

B1

SMD balun

SMD balun / filter

2.4 GHz

Wuerth

Johanson

Technology

748421245

2450FB15L0001

Filter included

CB1

CB3

LDO VREG

bypass capacitor

1 µF

(100nF minimum)

AVX

Murata

0603YD105KAT2A

GRM188R61C105KA12D

X5R

(0603)

10%

16V

CB2

CB4

Power supply bypass

capacitor

1 µF

(100nF minimum)

CX1, CX2

16MHz crystal load

capacitor

12 pF

AVX

Murata

06035A120JA

GRP1886C1H120JA01

COG

(0603)

5%

50V

CX3, CX4

32.768kHz crystal load

capacitor

12 … 25 pF

C1, C2

RF coupling capacitor

22 pF

Epcos

Epcos

AVX

B37930

B37920

06035A220JAT2A

C0G

5%

50V

(0402 or 0603)

C4 (optional) RF matching

0.47 pF

Johnstech

XTAL

Crystal

CX-4025 16 MHz

SX-4025 16 MHz

ACAL Taitjen

Siward

XWBBPL-F-1

A207-011

XTAL 32kHz

Crystal

Rs=100 kOhm

4.2 Extended Feature Set Application Schematic

The ATmega256/128/64RFR2 supports additional features like:

•

Security Module (AES)

•

High Data Rate Mode up to 2MBits/s

•

Antenna Diversity using alternate pin function DIG1/2 at Port G and F