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Design Notes
Final Schematic Status
Schematic connectivity is complete. ERC has zero unresolved critical/open findings. All unused MCU and optional connector pins are explicitly handled. PCB layout was not started.
Power Design
Positive rail
+6V input uses SS14 series reverse-polarity protection, 47 uF + 100 nF shunt capacitance, and a 2 A 600Ω@100MHz ferrite bead. LMR33630BDDAR generates +3.3V using the TI 1.4 MHz values: 2.2 uH inductor, 10 uF + HF input bypass, 2×22 uF output capacitance, 100 kΩ/43.2 kΩ feedback, 100 nF BOOT-SW, and 1 uF VCC bypass.
Negative rail
The negative protection diode is oriented with cathode at -6V_RAW and anode toward the protected load so normal return current can flow toward the negative source while reverse polarity is blocked. The rail uses 47 uF + 100 nF filtering, a 200 mA ferrite bead, then TPS7A3301RGW. The -2.5V set network is 115 kΩ/105 kΩ (nominal about -2.45V, inside ADMV8052 -2.6 to -2.4V range), with 47 uF input/output, 1 uF NR/SS and 10 nF FB-to-OUT feedforward.
Budget and thermal
High-performance STM32 profile assumes high clock/performance scale, internal-memory execution, USB FS, 10 MHz SPI and no external GPIO power loads. Datasheet representative high-performance all-peripheral current is 160 mA; conservative maximum envelope is 750 mA. Add 20 mA ADMV8052 dynamic budget and 10 mA for USB sensing/LEDs: 780 mA worst design load, 975 mA after 25% margin. The 3 A buck is comfortably sized. Estimated positive input current at 5.6V and 85% efficiency is about 0.68A at the margin load, within the 1A SS14 and connector path.
A linear +6V-to-3.3V solution would dissipate approximately 2.1W at 780mA and was rejected. The negative LDO dissipates only 87.5mW at the 25mA design limit and has ample headroom.
Crystal Calculation
Selected Y1: ABM8-25.000MHZ-B2-T3, 25MHz, CL=18pF, ESR 50Ω max, 3.2×2.5mm 4-pad SMD, active and distributor-listed. For equal capacitors:
CL = (C1×C2)/(C1+C2) + Cstray = C/2 + Cstray
Assume Cstray=3pF for MCU pins, package and short PCB traces. Therefore C=2×(18-3)=30pF. C25 and C26 are 30pF C0G/NP0. Validate startup margin and trim after first-board frequency measurement if layout parasitics differ materially.
MCU and Debug Decisions
- Preserve SPI1 PB3/PB4/PB5 mapping. PB3 remains SCLK.
- SWO is omitted from J5 because it conflicts with PB3. Header carries SWDIO, SWCLK, NRST, VTref and GND only; SWO/TDO and NC/TDI are intentional NCs.
- All VDD/VSS, VCAP, VDDA/VREF+, VBAT, BOOT0, NRST, HSE and USB pins are completed.
- PA8 drives the status LED; a second LED indicates +3.3V power.
RF Optional Networks
Each RF port includes a DNP 0402 series 0Ω footprint and DNP 0402 shunt capacitor footprint plus an RF probe pad. Populate only after VNA characterization; default assembly leaves the shunt footprints open and uses the 0Ω series links.
ADMV8052 CC-32-8 Figure 57 Record
Required package geometry from ADI Figure 57:
- Body: 22.00mm nominal square (21.85–22.15mm).
- Bottom reference: 20.20mm square perimeter extent and 15.82mm square inner reference.
- Perimeter pitch: 2.54mm BSC for straight runs; 2.49mm BSC around corner transitions.
- Corner pads 1, 9, 17, 25: 1.40mm square ±0.03mm.
- Pads 2–8 and 18–24: 1.40×1.50mm ±0.03mm.
- Pads 10–16 and 26–32: 1.50×1.40mm ±0.03mm.
- Center exposed pads: E1–E16 in a 4×4 array, 3.81mm BSC square cell pitch with 4.01mm reference and 0.20mm separation details per figure.
- Pin-1 identification is mandatory. Exposed pads are all GND and require paste segmentation and dense grounding vias during footprint authoring/layout.
Sole Remaining Blocker
The instantiated U1 backing part has a generated ~1.6mm footprint and cannot be made into the exact asymmetric CC-32-8 land pattern with a 4×4 exposed-pad array and segmented paste using the available project-level footprint tools. Component-owned footprint geometry must be corrected in the backing part project, published as a new version, and U1 updated. This is the only hard blocker before PCB work.
Verification
- Final schematic: 86 components, 54 nets.
- ERC: zero ERROR/WARNING/OPEN findings.
- Major-net readback confirms all STM32 supplies/grounds, SWD, USB, SPI, RF supplies and both regulators are connected.
- Manufacturing MPN review still flags generic passives/test pads because they intentionally remain parametric at schematic stage; each has a usable package/footprint. Final procurement MPN assignment can occur before manufacturing export.
Final Schematic Status
Power Design
Positive rail
Negative rail
Budget and thermal
Crystal Calculation
MCU and Debug Decisions
RF Optional Networks
ADMV8052 CC-32-8 Figure 57 Record
Sole Remaining Blocker
Verification
