[Hardware] Remove nRF7002 Wi-Fi from schematic & PCB — component removal + RF path redesign

[aaravgarg]

Parent: #6854

Components to Remove from Schematic & BOM

Ref	Part	Function	Sheet
U2	nRF7002	Wi-Fi 6 companion IC (QSPI to nRF5340)	Sheet 2
U3	LFD182G45DCHD277	RF diplexer — 2.4G/5G band split	Sheet 2
U10	FM8625H	RF switch — antenna sharing BLE/Wi-Fi	Sheet 2
U11	TPS22916C	Load switch — nRF7002 IOVDD power gating	Sheet 2
Q2	LN237N3T5G	N-ch MOSFET — RF switch control	Sheet 2
—	40MHz crystal (10ppm)	nRF7002 clock source	Sheet 2
L5	3.3µH 700mA 350mΩ	nRF7002 internal buck inductor	Sheet 2
C17	4.7µF	nRF7002 buck decoupling	Sheet 2
C31, C32	4.7µF	nRF7002 buck output caps	Sheet 2
R13, R15, R16, R17	100K	nRF7002 control line pull-ups/pull-downs	Sheet 2
—	Multiple 2.2µF, 220nF, 100nF	nRF7002 power rail decoupling	Sheet 2

Total: ~15-20 components removed from BOM.

RF Antenna Path Redesign

Current Path (with Wi-Fi)

nRF5340 ANT pin
    → Matching network (L3: 2.2nH, L4: 2.2nH, C12: 0.7pF, C15: 0.7pF)
    → FM8625H RF switch (controlled by GPIO P1.03)
    → LFD182G45DCHD277 diplexer (2.4G/5G split)
    → Antenna

New Path (BLE only)

nRF5340 ANT pin
    → Simplified matching network (needs retuning)
    → Antenna (direct)

Matching Network Redesign

The current matching (L3/L4 2.2nH, C12/C15 0.7pF NPO) was designed to compensate for the insertion loss of the RF switch (~0.5dB) and diplexer (~0.8dB). With those removed:

1. Must retune the matching network for direct 50Ω antenna feed
2. Use VNA (Vector Network Analyzer) to measure S11 (return loss) at 2.4GHz band
3. Target: S11 < -10dB across 2.400-2.4835 GHz (BLE channels 0-39)
4. The simplified path should actually improve BLE range — ~1.3dB less insertion loss
5. Start with Nordic's reference matching network for nRF5340 (see nRF5340 DK schematic) and iterate

RF Layout Notes

• The current layout has RF isolation requirements around the nRF7002 area (isolated ground planes on layer 2/3, via fencing). This can be relaxed.
• L1 placement constraint (">2.5mm from RF chip outer pads") no longer applies since the RF chip is removed.
• Antenna trace impedance: maintain 50Ω controlled impedance from nRF5340 to antenna feed point.
• Keep ground plane continuous under the antenna matching network — no cuts or splits.

QSPI Bus Removal

The entire QSPI peripheral connection to nRF7002 is removed:

nRF5340 Pin	Signal	Previous Use
P0.13	QSPI_IO0	nRF7002 data
P0.14	QSPI_IO1	nRF7002 data
P0.15	QSPI_IO2	nRF7002 data
P0.16	QSPI_IO3	nRF7002 data
P0.17	QSPI_SCK	nRF7002 clock
P0.18	QSPI_CSN	nRF7002 chip select

Note: The SPI NOR flash (P25Q16SH, U12) uses SPI3 (P1.07-P1.09), NOT QSPI. It is unaffected.

Coexistence Interface Removal

The BLE/Wi-Fi coexistence signaling between nRF5340 net core and nRF7002 is removed:

nRF5340 Pin	Signal	Previous Use
P0.24	grant-gpio	Coex grant (net core)
P0.28	req-gpio	Coex request (net core)
P0.29	swctrl1-gpio	Coex switch control
P0.30	status0-gpio	Coex status

RF Switch Control Removal

nRF5340 Pin	Signal	Previous Use
P1.03	rfsw_en	RF switch enable (app core GPIO)

nRF7002 Control Lines Removal

nRF5340 Pin	Previous Use
P0.29	nRF7002 control
P0.30	nRF7002 control
P0.31	nRF7002 control

Total: 12 GPIO Pins Freed

All freed pins should be left unconnected (NC) with optional test pads for future use.

Power Rail Changes

Remove from power architecture:

• VDD_BUCK (nRF7002 internal buck output)
• PALDO (nRF7002 PA LDO)
• PWRIOVDD (nRF7002 I/O domain, gated by U11 TPS22916C)

Remaining power rails (unchanged):

Rail	Voltage	Source
VBAT	3.0-4.2V	LiPo battery
VDD_3V3	3.3V	TPS628438 buck
VDD_1V8	1.8V	SGM2036S LDO

PCB Area Reclaimed

The nRF7002 + its support components occupy a significant portion of the PCB (estimated ~25-30% of the 25.5mm circular board). This freed area could be used for:

1. Larger battery — move from 150mAh 1654 to a larger cell if mechanically feasible
2. Better antenna — more ground plane area improves antenna performance
3. Simpler routing — fewer layers needed, potentially reduce from 4-layer to optimized 4-layer with better signal integrity
4. Future features — additional sensors, larger flash, etc.

Verification

• Schematic review: all nRF7002 connections removed, no floating nets
• BOM updated: all removed components flagged as DNP or deleted
• RF matching network redesigned and simulated/measured
• PCB layout updated with freed area
• Antenna impedance verified with VNA (S11 < -10dB at 2.4GHz)
• BLE range test on new board: equal or better than current
• DRC clean (no unconnected nets, no clearance violations)
• Gerber review before sending to fab