BSN N54

BSN-N54 (Nordic nRF54L variant)

Concluded at rev A. The N54 was compared with the C23 on rev A, and rev B uses the CC2340R5. See MCU_DECISION.md. This folder is kept as the record of that comparison.

KiCad project: BSN-N54.kicad_pro. See the root README for the board naming scheme.

Rev A (BSN-N54-A)

Ordered as a separate design from BSN-C23-A (not panelized). Firmware, bring-up procedure and per-board results: firmware/N54 and firmware/N54/BRINGUP.md.

Bring-up status

Test results

• RF: testing/RF/RF_CARRIER.md. HFXO trim 11.75 pF (+127 ppm at the datasheet 7 pF). The reference PA network as laid out costs 10–11 dB. Bypassed, the PA gives 0.0 dBm at the 0 dBm setting and +7.5 dBm at +8 dBm.
• Current: testing/Power/POWER_MEASUREMENTS.md. Floor 4.20 µA (System OFF 2.05 µA, both about 1.4 µA above the datasheet on both boards, cause not found), 7.6 µC per advert at 0 dBm, 2.01 / 1.78 µC per sensor reading with timer / DRDY wake (C23: 0.366 µA, 12.6 µC, 9.56 / 3.72 µC).

Rework log

Hand-modified boards are marked A* (see the root README).

ANT-pin matching network

The antenna matching network on the nRF54L05 ANT pin (U1 pin 31) is the Nordic reference PA network (nRF54L datasheet, circuit configuration 1 for QFN48: L2, C14, L3, C15, L4, C16), followed by the antenna match (L5, L6, L7) and the U.FL test point (R4, J1).

U1.ANT(31) ─ L2 ─┬─ L3 ─┬─ L4 ─┬──────────── L6 ─┬─ AE1
               C14    C15    C16   L5      │     L7
                │      │      │    │      R4     │
              VSS_PA  GND    GND  GND      │    GND
             (pin 32)                     J1

C14 grounds only to pin 32 (VSS_PA), which only joins the centre pad, and C15 grounds straight to the bottom plane with no inner-layer fill, as Nordic's notes require.

Measured on rev A: this network, as laid out with 0402 parts, cost 10–11 dB into 50 Ω (see testing/RF/RF_CARRIER.md). A rev B N54 should copy Nordic's 0201 layout exactly and verify the PA network into 50 Ω on its own before the antenna is matched.

Original Smith chart estimate (superseded)

Before the boards existed, the MCU source impedance and the antenna impedance were estimated from the nRF54L and antenna datasheets and stepped through all 8 elements on a Smith chart. This treated L5 as a series part, which it isn't on the board, and the estimated antenna impedance was later measured on C23 to be quite different (about 6.4 − j13 Ω, see hardware/C23/testing/rev_A/RF/ANTENNA_MATCHING.md). Kept for reference:

https://onlinesmithchart.com/?circuit=blackBox_34.1_-40.9_0__seriesInd_2.7_nH_0_0__shortedCap_1.5_pF_0_0_0__seriesInd_3.5_nH_0_0__shortedCap_2_pF_0_0_0__seriesInd_3.5_nH_0_0__shortedCap_0.3_pF_0_0_0__shortedInd_7.3_nH_0_0__seriesInd_6.7_nH_0_0&fSpan=0

A simplified 3-element equivalent from the same estimate:

https://onlinesmithchart.com/?circuit=blackBox_34.1_-40.9_0__seriesInd_4.2_nH_0_0__shortedCap_0.3_pF_0_0_0__seriesInd_6.7_nH_0_0&fSpan=0