Root/ecn/ecn0003.txt

Source at commit 49e7c83796bc04941e9dbcec69bc0751563ff4d4 created 2 years 5 months ago.
By Werner Almesberger, atusb/: use ""VDD" symbol from kicad-libs
1Replace balun and filter with integrated balun
2
3
4We consider the balun needs for the AT86RF230 and the TI/Chipcon
5CC2520 we may try as a design alternative.
6
7For the AT86RF230, Atmel recommend baluns with integrated filter,
8namely the Wuerth 748421245 and the Johanson 2450FB15L0001, both in the
9AR86RF230 data sheet.
10
11For the CC2520, TI recommend a microstrip-based design for the balun,
12both in the CC2420/CC243x/CC2480 application note [1] and the reference
13design [2], without fully characterizing neither the transceiver's RF
14output nor all the components in the balun.
15
16Johanson lists the 2450FB15L0001 [3] and even a 2450BM15B0002 [3] for
17the TI/Chipcon CC2520, but not even Octoparts is able to find a
18distributor for these parts.
19
20Digging deeper, TI reveal more information about the balun in [5].
21
22Finally, TI somewhat hesitatingly acknowledge that the Murata balun
23LDB182G4510C-110 can be used for the CC2520 [6], with a 3.9 nH inductor
24connecting RF_P and RF_N, the balun coupled to GND not directly but via
2510 nF, and finally an LC low-pass filter with 1.5 nH and 2.2 pF at the
26output, for EMI compliance.
27
28Note that this also means that CC2520 and AT86RF230 both have an
29impedance of 100 Ohm.
30
31A balun without filter similar to the Murata part would be the Johanson
322450BL15K100.
33
34Manufacturer Part number Package Digi-Key Price/Qty
35--------------- ----------------------- ------- --------------- ---------------
36Wuerth 748421245 0805-6 732-2230-1-ND 2.15/25
37                        732-2230-2-ND 0.753/4000
38Johanson 2450FB15L0001 0805-6 - -
39Johanson 2450BM15B0002 0805-6 - -
40Johanson 2450BL15K100 0805-6 712-1045-1-ND 0.488/10
41                        712-1045-2-ND 0.225/4000
42Murata LDB182G4510C-110 0603-6 490-5023-1-ND 0.325/10
43                        490-5023-2-ND 0.114/4000
44
45[1] http://www.ti.com/litv/pdf/swra098d
46[2] http://focus.ti.com/docs/toolsw/folders/print/cc2520em_refdes.html
47[3] http://www.johansontechnology.com/images/stories/ip/baluns/Balun_Filter_Combo_Matched_2450FB15L0001_v11.pdf
48[4] http://www.johansontechnology.com/images/stories/ip/baluns/balun_filter_combo_matched_2450bm15b0002_v2.pdf
49[5] http://www.ti.com/litv/pdf/swra236a
50[6] http://e2e.ti.com/support/low_power_rf/f/155/t/15910.aspx
51
52
53Conclusion: the Wurth balun appears to be the safest choice for
54prototyping the AT86RF230. Due to its high cost, a circuit with a
55discrete filter may be considered for larger quantities.
56
57For the CC2520, it's probably safest to directly try the Muarta balun
58with the recommended discrete filtering circuit.
59

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