AVR RF/ Atmel

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For customers designing Atmel Corporation

We are pleased to introduce you to our crystal unit

  Items to Confirm (designing of oscillation circuit)

· Selection Guidance for crystal unit

· Crystal Products Lineup

· Oscillation Circuit and Selection Guidance of Crystal Unit.

· Precautions for designing of PCB Board

Crystal Recommendations for Atmel Corporation "AVR RF chips".

· Recommendations AVR RF chips.

> Clock solution recommendations for Atmel Corporation AVR RF chips

In realizing low power consumption RF designs, the following factors should be taken into consideration.

1. Oscillation start-up time

2. Frequency tuning

3. Lower BER(Bit Error Rate) over operating temperature

No.	Oscillation Circuit Factor	2.4 GHz
		< AT crystal unit spec.>
1	Quick oscillation start-up time *High oscillation allowance *Boost inverter	*Lower ESR(R1) *High drive level
2	Easy frequency control *inner frequency tuning capacitor	*proper frequency sensitivity *low parameters' variation
3	Lower BER *temperature compensation	*High frequency stability

MHz Crystal equivalent circuit
Rapid Oscillation start-up time → Lower ESR (R1) , Higher C1 → Higher drive level
Suitable Frequency Tuning → Lower parameters variation(C0,C1,L1,ESR)
Suitable Frequency Tuning → Proper Sensitivity (CL,C0)
Higher Frequency Stability → Stable fSTA
QMEMS Technology

Clock solution recommendations for Atmel Corporation AVR RF chips

Worldwide				ATmega256RFR2 ATmega128RFA1	AT86RF233 AT86RF231	AT86RF212B AT86RF212
US	Europe	Japan	Asia
ZigBee IEEE802.15.4				2400 to 2483.5 MHz		700/800/900 MHz
Recommendable Clock Devices				S2520-16.000M-9-20-20-A 16MHz,9pF

Notes: Above recommendations are based on actual evaluation results and intended to support users in picking the right components. As the actual board layout and choice of external components influences the best suitable crystal load capacitance, We does not assume any responsibility and grant warranty for above recommendations. Users design must be verified and decided by own and individual evaluation.
Please refer to Atmel Corporation AVR RF chips manual for designing.

*ZigBee is a registered trademark of Koninklijke Philips Electronics N.V.

Items to Confirm (designing of oscillation circuit)

Please note: to design oscillation circuit, you need to confirm the electronic characteristics as follows:

Oscillation allowance and Negative resistance (-R):
You need to confirm oscillation capability.
We recommend the condition: (-R) / ESR > 5
* -R: Negative resistance, ESR: Equivalent Series Resistance
Drive Level:
You need to confirm if oscillation is stable, and if the drive level is within the specification.
Load Capacitance:
Load capacitance affects frequency stability, oscillation allowance, negative resistance, and start-up time of oscillation.
In addition the load capacitance is determinative factor of crystal unit's load capacitance (CL value) directly.
* frequency stability: frequency deviation out of circuit conditions.

Selection Guidance for crystal unit

When Customer selects crystal unit, ｌload capacitance (CL value) is an important factor of the selection.
For instance, crystal with small CL(7.0 pF) makes larger oscillation allowance, smaller current consumption and worse frequency stability, like below table.
Oppositely, crystal with large CL(12.5 pF) makes smaller oscillation allowance, larger current consumption and better frequency stability.
Please select it in consideration of these characteristics.

StrongFirst Crystal Product Lineup

Product	Size [mm]	Applications	Images
S2520	2.5×2.0×0.55t	-Mobile phone,Bluetooth,W-LAN -ISM band,Clock for MPU

Oscillation Circuit and Selection Guidance of Crystal Unit for AVR RF chips

Pin number of XTAL1/XTAL2

	XTAL1	XTAL2
ATmega256RFR2	57	56
ATmega128RFA1	57	56
AT86RF23x, 212/212B	26	25

Internal trimming capacitors of AVR RF chips (Default)

Ctrim (XTAL_TRIM)

0

pF

IC name	product name	Freq.[Hz]	CL*1 [pF]	f_tol*2 [ppm]	Product Code*3	External parts *4		Package size[mm] WxDxH
						Cg [pF]	Cd [pF]
ATmega256RFR2	S2520	16M	9.0	10	S2520-16.000M-9-10-10-A	12	12	2.5x2.0x0.55
ATmega128RFA1
AT86RF233				20	S2520-16.000M-9-20-20-A	12	12
AT86RF231
AT86RF212B
AT86RF212

Notes:*

1. Load capacitance.

2. Frequency tolerance (standard)

3. Two digits of the product code is packing specification, please refer here for the detail.

4. Above recommendations are based on actual evaluation results and intended to support users in picking the right components. And the results are only according to the sample set that received from our customers, so it is not including the dispersion trend of IC and the external parts.
As the actual board layout and choice of external components influences the best suitable crystal load capacitance, We do not assume any responsibility and grant warranty for above recommendations. Users design must be verified and decided by own and individual evaluation.

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