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SF32LB52x Hardware Design Guide — Design Review Checklist and References

Part of the SF32LB52x Hardware Design Guide

This page covers Sections 7-10: Design Review Checklist, Related Documents and References, Appendices, and Revision History. Return to PCB Layout Guidelines.

7. Design Review Checklist

  • Minimum-system review is complete: exact variant, package, power tree, boot medium, bootstrap pins, debug/download access, clocks, and wake strategy are all documented
  • The exact chip model and power variant are confirmed, and power schematics from the two variants are not mixed
  • Processor power pins (VBUS/VBAT/VCC, or PVDD/VDDIOA/VDD_SIP) are within the datasheet voltage range
  • BUCK inductor meets 4.7 uH ±20%, DCR ≤0.4 Ω, Isat ≥450 mA
  • Battery-powered variant: charging path, OVP device voltage range, and integrated-LDO output capacitance are verified
  • 48 MHz and 32.768 kHz crystals meet the recommended specifications, with routing and keep-out zones satisfied
  • RF trace is 50 Ω impedance, with the matching network placed close to the chip
  • Storage boot configuration (including the regular-powered variant's eMMC option) matches the Bootstrap pin settings
  • Storage power switches are uniformly controlled through PA21, active high (on) / low (off)
  • USB and SDIO differential trace impedance and length matching meet requirements
  • DBG_UART/SWD multiplexed pins and production test points are reserved
  • Key component part numbers have been verified against the latest SiFli Approved Vendor List

Additional source references:

The Schematic Checklist (Section 5.8) and PCB Layout Checklist (Section 6.15) reproduce the same SF32LB52 Schematic & PCB Checklist (V1.0, 2026-01-21) item by item, alongside the schematic and PCB layout guidance they check against.

9. Appendices

The original SiFli application notes include the following schematic, PCB layout, mechanical, and power reference figures. These appendices preserve those source figures for review evidence, while Sections 5 and 6 remain the primary design guidance.

How to use these figures

Treat these figures as reference circuits and layout examples from the source application notes. Use the rule text, tables, datasheet, reference manual, latest reference design package, and AVL to confirm the final implementation for the exact device and product.

Table 9-1: Appendix Map
Need Start Here
Smart watch block-diagram examples for both SF32LB52x design groups Appendix A: A Typical Smart Watch Application
Circuit-level schematic examples for RF, storage/boot, buttons, motor, audio, clock, USB, and DC/DC Appendix B: Reference Schematics
PCB placement and routing examples for RF, storage, audio, stack-up, fanout, clock, USB, and DC/DC Appendix C: Reference PCB Layouts
Package outline, shape, and land-pattern drawings Appendix D: Mechanical
Charging, OVP, power-tree, and PMU reference circuits and layouts Appendix E: Power

Appendix A. A Typical Smart Watch Application

A typical SF32LB52x smart watch design includes the MCU, display, touch controller, storage, sensors, vibration motor, audio input/output, Bluetooth antenna, clock sources, power management, debug access, and production-test access. The battery-powered design additionally includes charging management.

Figure A-1: SF32LB520/3/5/7 Smart Watch Application Diagram

Figure A-1: SF32LB520/3/5/7 Smart Watch Application Diagram

Figure A-2: 52B/D/E/G/J Smart Watch Application Diagram

Figure A-2: 52B/D/E/G/J Smart Watch Application Diagram

Appendix B. Reference Schematics

RF

Figure B-1: RF Front-End Block Diagram

Figure B-1: RF Front-End Block Diagram

Figure B-2: RF Schematic Reference

Figure B-2: RF Schematic Reference

Figure B-3: RF Schematic Routing Reference

Figure B-3: RF Schematic Routing Reference

Storage and Boot

Figure B-4: SF32LB520/3/5/7 Bootstrap Reference

Figure B-4: SF32LB520/3/5/7 Bootstrap Reference

Figure B-5: 52B/D/E/G/J Bootstrap Reference

Figure B-5: 52B/D/E/G/J Bootstrap Reference

Figure B-6: SDIO Schematic Reference

Figure B-6: SDIO Schematic Reference

Buttons, Motor, and Audio

Figure B-7: SF32LB520/3/5/7 Vibration Motor Reference

Figure B-7: SF32LB520/3/5/7 Vibration Motor Reference

Figure B-8: 52B/D/E/G/J Vibration Motor Reference

Figure B-8: 52B/D/E/G/J Vibration Motor Reference

Figure B-9: Power Key Reference

Figure B-9: Power Key Reference

Figure B-10: Rotary Encoder Key Reference

Figure B-10: Rotary Encoder Key Reference

Figure B-11: Analog MEMS Microphone Reference

Figure B-11: Analog MEMS Microphone Reference

Figure B-12: Analog ECM Microphone Reference

Figure B-12: Analog ECM Microphone Reference

Figure B-13: Analog DAC to PA Reference

Figure B-13: Analog DAC to PA Reference

Figure B-14: Audio Power Schematic Reference

Figure B-14: Audio Power Schematic Reference

Figure B-15: Audio ADC Schematic Reference

Figure B-15: Audio ADC Schematic Reference

Figure B-16: Audio DAC Schematic Reference

Figure B-16: Audio DAC Schematic Reference

Clock

Figure B-17: 48 MHz Crystal Schematic

Figure B-17: 48 MHz Crystal Schematic

Figure B-18: 32.768 kHz Crystal Schematic

Figure B-18: 32.768 kHz Crystal Schematic

USB

Figure B-19: USB Schematic Reference

Figure B-19: USB Schematic Reference

DC/DC

Figure B-20: DC/DC Schematic Reference

Figure B-20: DC/DC Schematic Reference

Appendix C. Reference PCB Layouts

RF

Figure C-1: RF PCB Matching Reference

Figure C-1: RF PCB Matching Reference

Figure C-2: RF PCB Routing Reference

Figure C-2: RF PCB Routing Reference

Storage

Figure C-3: SDIO PCB Reference

Figure C-3: SDIO PCB Reference

Audio

Figure C-4: Audio Power PCB Reference

Figure C-4: Audio Power PCB Reference

Figure C-5: Audio ADC PCB Reference

Figure C-5: Audio ADC PCB Reference

Figure C-6: Audio DAC PCB Reference

Figure C-6: Audio DAC PCB Reference

PCB Foundation

Figure C-7: PCB Stack-Up Reference

Figure C-7: PCB Stack-Up Reference

Figure C-8: PCB Design Rule Reference

Figure C-8: PCB Design Rule Reference

Figure C-9: QFN Fanout Reference

Figure C-9: QFN Fanout Reference

Figure C-10: Crystal Placement Reference

Figure C-10: Crystal Placement Reference

Clock Routing

Figure C-11: 48 MHz Crystal Routing Model

Figure C-11: 48 MHz Crystal Routing Model

Figure C-12: 48 MHz Crystal Routing Reference

Figure C-12: 48 MHz Crystal Routing Reference

Figure C-13: 32.768 kHz Crystal Routing Model

Figure C-13: 32.768 kHz Crystal Routing Model

Figure C-14: 32.768 kHz Crystal Routing Reference

Figure C-14: 32.768 kHz Crystal Routing Reference

USB

Figure C-15: USB PCB Reference

Figure C-15: USB PCB Reference

Figure C-16: USB Layout Reference

Figure C-16: USB Layout Reference

Figure C-17: USB Routing Reference

Figure C-17: USB Routing Reference

DC/DC

Figure C-18: DC/DC PCB Reference

Figure C-18: DC/DC PCB Reference

Appendix D. Mechanical

Figure D-1: SF32LB520/3/5/7 Package Layout

Figure D-1: SF32LB520/3/5/7 Package Layout

Figure D-2: 52B/D/E/G/J Package Layout

Figure D-2: 52B/D/E/G/J Package Layout

Figure D-3: QFN68L Package Dimensions

Figure D-3: QFN68L Package Dimensions

Figure D-4: QFN68L Package Shape

Figure D-4: QFN68L Package Shape

Figure D-5: QFN68L Recommended Footprint

Figure D-5: QFN68L Recommended Footprint

Appendix E. Power

SF32LB520/3/5/7 (Battery-Powered)

Figure E-1: External Charger Without PPM

Figure E-1: External Charger Without PPM

Figure E-2: External Charger With PPM

Figure E-2: External Charger With PPM

Figure E-3: Integrated Charger Circuit

Figure E-3: Integrated Charger Circuit

Figure E-4: OVP Threshold Setting

Figure E-4: OVP Threshold Setting

Figure E-5: Adjustable OVLO OVP Application

Figure E-5: Adjustable OVLO OVP Application

Figure E-6: Regulated-Output OVP Application

Figure E-6: Regulated-Output OVP Application

Figure E-7: SF32LB520/3/5/7 Power Structure

Figure E-7: SF32LB520/3/5/7 Power Structure

Figure E-8: VCC Schematic Reference

Figure E-8: VCC Schematic Reference

Figure E-9: VCC PCB Reference

Figure E-9: VCC PCB Reference

Figure E-10: Charging Schematic Reference

Figure E-10: Charging Schematic Reference

Figure E-11: Charging PCB Reference

Figure E-11: Charging PCB Reference

Figure E-12: PMU TVS Reference

Figure E-12: PMU TVS Reference

Figure E-13: PMU EOS Reference

Figure E-13: PMU EOS Reference

52B/D/E/G/J (Regular-Powered)

Figure E-14: 52B/D/E/G/J PMU PCB Reference

Figure E-14: 52B/D/E/G/J PMU PCB Reference

10. Revision History

Table 10-1: Revision History
Version Date Note
1.1 2026-07 Promoted Power System to a peer schematic section, split Clock Generation and RF into separate schematic sections, and renumbered the following schematic guidance sections.
0.0.1 10/2024 Original release of SF32LB520-3-5-7-HW-Application
0.0.1 10/2024 Original release of SF32LB52B-E-G-J-HW-Application
1.0 This document Combined both official hardware application notes into a single guide, using tabs to separate battery-powered vs. regular-powered variant content

10.1. Checklist Revision History

The item-by-item checklist in the Schematic Checklist and PCB Layout Checklist is versioned separately from the guide, following SiFli's own SF32LB52 Schematic & PCB Checklist spreadsheet.

Table 10.1-1: Checklist Revision History
Version Date Note
1.0 2026-01-21 Initial release, based on SiFli's SF32LB52 Schematic & PCB Checklist V1.0