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Is ST's BAL-NRF01D3 balun compatible with the nRF8001?

Garth Snyder

In the past I've used the Johanson 2450BM14A0002 balun with the nRF8001 with great success. Unfortunately, it's now out of stock throughout the US at component retailers, and more supply isn't expected for a couple of months.

Do you know if the BAL-NRF01D3 from STMicroelectronics is a suitable substitute? There is some evident cross-compatibility with the Johanson balun, but the compatibility lists are not identical, and in particular, ST does not explicitly list the nRF8001 as a compatible device. But I thought perhaps this might be more due to product line updates than to an actual incompatibility. (The Johanson balun predates the nRF8001; it was retroactively certified as compatible.)

My application is a short-run board that does not need regulatory certification; it just has to work reasonably well. (So with reference to another thread about the ST balun, no, I don't have to do battle with the South Korean regulatory authorities. :-)

I'm asking here (rather than asking ST) because you folks probably have a much better idea of how similar or different the Nordic RF chips are from each other.

The BAL-NRF01D3 data sheet is here. Claimed compatibility is nRF24LE1 QFN-32 pins, nRF24AP2-1CH, nRF24AP2-8CH, nRF51422-QFAA (build code CA/C0), nRF51822-QFAA (build code CA/C0) and nRF51822-QFAB (build code AA/A0).

The 2450BM14A0002 data sheet is here. Claimed compatibility is nRF24L01, nRF24L01+, nRF24LE1, nRF24LU1, nRF24AP2, and nRF8001.

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    The Johanson balun was originally developed for the nRF24L01(+). Since the radio part of the nRF24-series is similar, the balun could also be used for other devices as well. But the length of the internal bonding wires are different. So that's why the distance between the chip and the balun are not the same. The nRF24LE1 and nRF8001 have shorter bonding wires than the nRF24L01 so the missing inductance must be compensated for by adding some track length in between.

    Now, the nRF8001 have longer bonding wires than the nRF24LE1. So a balun made for the nRF24LE1 should be placed closer to the nRF8001. The difference isn't large, so I guess you can place the ST balun as close as possible to the nRF8001 and make it work. I have't tried this though. But you should get decent output power by doing so.

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    Thanks for being willing to speculate - this is very helpful.

    If I try this out, I'll report back here how it goes. Unfortunately, I don't have quantitative RF test equipment, so all I will be able to say is that it seemed to work (or didn't :-).

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