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8393CS-MCU Wireless-09/14

ATmega256/128/64RFR2

4 Application Circuits

4.1 Basic Application Schematic

A basic application schematic of the ATmega256/128/64RFR2 with a single-ended RF

connector is shown in Figure 4-1 below and the associated Bill of Material in Table 4-1

on page 10. The 50Ω single-ended RF input is transformed to the 100Ω differential RF

port impedance using Balun B1. The capacitors C1 and C2 provide AC coupling of the

RF input to the RF port, capacitor C4 improves matching.

Figure 4-1. Basic Application schematic (64-pin package)

8

7

6

5

4

3

2

1

17

18

19

20

21

22

23

24

56

57

58

59

60

61

62

63

AVSS

RFP

RFN

AVSS

TST

41

42

43

44

45

46

47

48

PB0

DVSS

PE0

PB7

CB3

CB4

RSTN

XTAL

CX1

CX2

CB1

CB2

C1

C2

B1

RF

C4

25

26

27

28

29

30

31

32

16

14

13

12

11

10

9

15

64

54

55

49

50

51

52

53

33

34

35

36

37

38

39

40

RSTON

XTAL

32kHz

CX3

CX4

CLKI

DEVDD

DVSS

DEVDD

PF7

PG0

Pins TST & CLKI

must be connected

The power supply bypass capacitors (CB2, CB4) are connected to the external analog

supply pin (EVDD, pin 59) and external digital supply pin (DEVDD, pin 23). Pins 34, 44

and 54 supply the digital port pins.

Floating pins can cause excessive power dissipation (e.g. during power on). They

should be connected to an appropriate source. GPIO shall not be connected to ground

or power supply directly.

The digital input pins TST and CLKI must be connected. If pin TST will never be used it

can be connected to AVSS while an unused pin CLKI could be connected to DVSS (see

chapter "Unused Pins" on page 7).

Capacitors CB1 and CB3 are bypass capacitors for the integrated analog and digital

voltage regulators to ensure stable operation and to improve noise immunity.