2010-08-26 06:30:41 +03:00
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Replace balun and filter with integrated balun
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2010-08-26 21:41:14 +03:00
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We consider the balun needs for the AT86RF230 and the TI/Chipcon
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CC2520 we may try as a design alternative.
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For the AT86RF230, Atmel recommend baluns with integrated filter,
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namely the Wuerth 748421245 and the Johanson 2450FB15L0001, both in the
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AR86RF230 data sheet.
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For the CC2520, TI recommend a microstrip-based design for the balun,
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both in the CC2420/CC243x/CC2480 application note [1] and the reference
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design [2], without fully characterizing neither the transceiver's RF
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output nor all the components in the balun.
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Johanson lists the 2450FB15L0001 [3] and even a 2450BM15B0002 [3] for
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the TI/Chipcon CC2520, but not even Octoparts is able to find a
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distributor for these parts.
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Digging deeper, TI reveal more information about the balun in [5].
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Finally, TI somewhat hesitatingly acknowledge that the Murata balun
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LDB182G4510C-110 can be used for the CC2520 [6], with a 3.9 nH inductor
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connecting RF_P and RF_N, the balun coupled to GND not directly but via
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10 nF, and finally an LC low-pass filter with 1.5 nH and 2.2 pF at the
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output, for EMI compliance.
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Note that this also means that CC2520 and AT86RF230 both have an
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impedance of 100 Ohm.
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A balun without filter similar to the Murata part would be the Johanson
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2450BL15K100.
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Manufacturer Part number Package Digi-Key Price/Qty
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--------------- ----------------------- ------- --------------- ---------------
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Wuerth 748421245 0805-6 732-2230-1-ND 2.15/25
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732-2230-2-ND 0.753/4000
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Johanson 2450FB15L0001 0805-6 - -
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Johanson 2450BM15B0002 0805-6 - -
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Johanson 2450BL15K100 0805-6 712-1045-1-ND 0.488/10
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712-1045-2-ND 0.225/4000
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Murata LDB182G4510C-110 0603-6 490-5023-1-ND 0.325/10
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490-5023-2-ND 0.114/4000
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[1] http://www.ti.com/litv/pdf/swra098d
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[2] http://focus.ti.com/docs/toolsw/folders/print/cc2520em_refdes.html
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[3] http://www.johansontechnology.com/images/stories/ip/baluns/Balun_Filter_Combo_Matched_2450FB15L0001_v11.pdf
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[4] http://www.johansontechnology.com/images/stories/ip/baluns/balun_filter_combo_matched_2450bm15b0002_v2.pdf
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[5] http://www.ti.com/litv/pdf/swra236a
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[6] http://e2e.ti.com/support/low_power_rf/f/155/t/15910.aspx
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Conclusion: the Wurth balun appears to be the safest choice for
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prototyping the AT86RF230. Due to its high cost, a circuit with a
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discrete filter may be considered for larger quantities.
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For the CC2520, it's probably safest to directly try the Muarta balun
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with the recommended discrete filtering circuit.
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