component

BMM350_Bosch_v1

Unreviewed

by Kyle Bergstedt

9-contact breakout for the Bosch BMM350 WLCSP magnetometer. Separate 1.8 V VDD rail. Default address 0x15 (ADSEL pulled high via R5).

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bmm350-bosch-v1-075000 / README.md
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BMM350 Molecule — Hardware Reference

Compact 9-contact breakout for the Bosch BMM350 3-axis magnetometer (WLCSP). Brings out separate VDD and VDDIO rails (the BMM350 has a stricter VDD range than most Bosch parts).

  • Source: adom-inc/bosch-molecules/Moecule_BMM350_Bosch_V1 — imported 2026-04-17 (folder name misspelled Moecule upstream; we preserve that on disk)
  • KiCad project: Moecule_BMM350_Bosch_V1.kicad_pro
  • Wiki page: molecules/bmm350-bosch-v1-075000
  • Board: 9 contacts — 4 corner mount-pins carry I²C + VDDIO, 3 side contacts carry VDD / INT / address strap, silk revision V1: 2025-09-03
  • IC: BMM350 (Bosch BGA-9, 1.28 × 1.28 × 0.5 mm WLCSP, U1)

Component summary

Ref Part Function
U1 BMM350 3-axis magnetometer
C1 2.2 µF 0805 X7R CRST reset / reservoir cap (schematic note: "CRST 2.2uF Recommended, X7R")
C2 100 nF 0402 VDDIO decoupling
C3 100 nF 0402 VDD decoupling
R5 10 kΩ 0402 Default pull-up from +VDDIO → /0x15 strap net (→ default address 0x15)

External contact map

Positions in mm on the front copper. Two columns: west (X=139.8) and east (X=147.8).

West edge

Ref Silk Net Role
MP2 VDDIO +VDDIO Logic rail — 1.72–3.6 V
MC6 VDD (silk y) +VDD Analog rail — 1.72–1.98 V only (tight tolerance!)
MC4 INT BMM_INT Interrupt (push-pull or open-drain, pull-up at host if OD)
MP1 GND GND Ground

East edge

Ref Silk Net Role
MP3 SDA (silk BMM350) BMM_SDA I²C SDA
MC12 BMM350 /0x15 Strap test-point (pulled to +VDDIO via R5)
MC3 ADSEL BMM_ADSEL/0x14/0x15 I²C address select — routed to U1 pin B2
MC10 0x14 GND Strap option: bridge MC3 ↔ MC10 for 0x14
MP4 SCK BMM_SCK I²C SCL

I²C address strap

BMM350 I²C slave address is set by ADSEL at power-up:

ADSEL tied to I²C address
GND (bridge MC3 ↔ MC10, silk 0x14) 0x14
+VDDIO (default — R5 pull-up to /0x15 net) 0x15 (demo firmware target ✓)

Schematic text: "ADSEL (Legacy I2C, LSB): GND = 0x14, VDDIO = 0x15."

Default is 0x15 — matches the firmware. Unless you intend to run it at 0x14, leave MC3 / MC10 unbridged.

Address conflict check on the arm bus

The arm I²C bus has: BMI270 @ 0x68, BMA400 @ 0x14, BMA580 @ 0x18, BMM350 @ 0x15 (this molecule), BHI360 @ 0x28, BHI385 @ 0x29.

If you accidentally strap BMM350 to 0x14 it will collide with the BMA400 on the same bus.

Power

Rail Voltage Source
VDD (analog) 1.72–1.98 V 1.8 V supply required — cannot run at 3.3 V
VDDIO 1.72–3.6 V Host via MP2 (3.3 V in demo)

This is the one molecule in the arm bus that needs a 1.8 V rail. The HARDWARE_CONFIG.md power plan uses the 1.8 V LDO (fed from 3.3 V) for BMV080 core + BHI360 VDD + BHI385 VDD + BMM350 VDD. Do not accidentally tie MC6 (silk y = VDD) to 3.3 V — that exceeds the BMM350 absolute maximum.

Also from schematic: "VDDIO is 300 mV max when VDD = 0 V." If you shut off VDD during operation, VDDIO must drop too or the chip sustains stress. Not an issue if both rails come up together and stay up.

Typical active current: 200 µA.

Interrupt

INT (MC4) is software-configurable for data-ready, FIFO watermark, or threshold events. Output can be push-pull or open-drain; if open-drain, supply an external pull-up on the host (not present on this molecule).

Magnetic field range

Schematic annotation: "Max ±2000 µT: (Bx, By, Bz < 0.75 × 2400 µT)." The BMM350's full-scale is ±2400 µT on each axis, and for linear behavior Bosch recommends staying under 2000 µT. Keep magnets / motors / ferrous tooling away from the mounted sensor.

Wiring to the Arm RM2 I²C bus

BMM350 MP2 (VDDIO) ──── RM2 +3V3
BMM350 MC6  (VDD)  ──── +1.8 V rail (NOT +3V3!)
BMM350 MP1 (GND)   ──── RM2 GND
BMM350 MP3 (SDA)   ──── RM2 GPIO4 (I²C0 SDA, shared bus)
BMM350 MP4 (SCK)   ──── RM2 GPIO5 (I²C0 SCL, shared bus)
BMM350 MC4 (INT)   ──── (optional; if open-drain, needs external pull-up)
BMM350 MC3 (ADSEL) ──── (leave floating — default 0x15 via R5 pull-up)

Gotchas for firmware bring-up

  • VDD is 1.8 V only. Do not feed 3.3 V into MC6 — the BMM350 will be damaged. This is the most common wiring mistake on the arm bus.
  • Default address is 0x15 (matches firmware). Only bridge MC3↔MC10 if you explicitly want 0x14.
  • CRST cap (C1, 2.2 µF X7R) is on-board — no external reset circuitry needed. But if you see the sensor NACKing after a brown-out, verify C1 is charging properly and the supply is stable.
  • BMM350 OTP trim + self-test must run at init before the first measurement — already handled in firmware/sensors/bmm350.c.
  • No 4.7 kΩ I²C pull-ups on this board — provided by the RM2 carrier / main arm bus.