原标题：Maxim MAX32620超低功耗可穿戴健康传感器平台方案

　　Maxim公司的MAXREFDES100#是健康传感器(hSensor)设计平台,集成了生物模拟前端解决方案(MAX30003),脉氧和心率传感器(MAX30101),两个人体温度传感器(MAX30205),三轴加速度器,3D加速度器和3D陀螺仪和气压传感器,支持运动测量,精密皮肤温度和各种生物电测量,包括ECG,EMG和EEG,以及三个波长(880nm,660nm,537nm)的脉搏血氧和心率检测.本文介绍了超低功耗MCU MAX32620/MAX32621主要特性,典型应用电路和MAXREFDES100#健康传感器(hSensor)设计平台框图,电路图,材料清单和PCB设计图.

　　The MAX32620/MAX32621 is a 32-bit RISC ARM® Cortex®-M4F (M4 plus Floating Point Unit) microcon­troller. It is ideally suited for the emerging category of medical and fitness applications. The architecture com­bines high-efficiency,signal-processing functionality with low cost, and ease of use. The device features 4 powerful & flexible power modes. Built-in dynamic clock gating and firmware controlled power gating minimize power con­sumption for any application.Multiple SPI, UART, and I2C serial interfaces,as well as a 1-Wire® master and USB,allow for interconnection to a wide variety of external sen­sors.A four-input, 10-bit ADC with selectable references is provided.

　　The MAX32621 is a secure version of the MAX32620, incorporating a trust protection unit (TPU) with encryption and advanced security features.

　　MAX32620/MAX32621优势和特性:

　　High-Efficiency Microcontroller for Rechargeable Devices Internal Oscillator Operates Up to 96MHz

　　Floating Point Unit

　　Memory Protection Unit

　　2MB Flash Memory

　　256KB SRAM

　　8KB Instruction Cache

　　1.2V ±5% Core Supply Voltage

　　1.8V ±5% I/O and Analog Supply Voltage

　　Optional 3.3V ±5% USB Supply Voltage

　　Tiny 81-Ball WLP Minimizes Board Space (3.9mm x 3.9 mm WLP, 0.4 mm Pitch)

　　Power Management Maximizes Uptime for Battery Applications 95μA/MHz Active Executing from Flash

　　600nA Low Power (LP0) Mode with RTC enabled

　　2.5μA Ultra-Low Power Data Retention Mode(LP1)with Fast 5μs(typ)Wakeup to 96MHz

　　Peripheral Management Unit (PMU) Reduces Power Consumption in Measurement Mode (LP2)

　　Optimal Peripheral Mix Provides Platform Scalability Three SPI Masters, Four UARTs, Three I2C Mas­ters, and One 1-Wire Master

　　49 General-Purpose I/O Pins

　　SPI Execute in Place Engine for Memory Expan­sion with Minimal Footprint

　　Full-Speed USB 2.0 with Internal Transceiver

　　Sixteen Pulse Train Engines

　　Four-Input, 10-Bit Sigma-Delta ADC Operating at 7.8 kS/s

　　Trust Protection Unit (TPU) Secures Valuable IP and Data (MAX32621 Only) Robust Hardware Internal Security

　　High-Speed Modular Arithmetic Accelerator (MAA) Supports Fast ECDSA

　　AES Hardware Engine

　　Hardware PRNG Entropy Generator

　　Secure Boot Loader

　　MAX32620/MAX32621应用:

　　Sport Watches

　　Fitness Monitors

　　Wearable Medical Patches

　　Portable Medical Devices

　　Sensor Hub

　　图1.MAX32620/MAX32621功能框图

　　图2.MAX32620/MAX32621时钟框图

　　图3.MAX32620/MAX32621典型应用电路:ECG贴片

　　MAXREFDES100#健康传感器(hSensor)设计平台

　　Maxim builds complex and innovative solutions for medical and high-end fitness applications. These solutions are primarily stemming from multiple product lines within Maxim. In order to help customers evaluate the features of these solutions quickly and enable them with their designs, Maxim developed an integrated sensor platform called "hSensor" Platform. With this platform, customers can evaluate our portfolio faster and more easily for multiple use cases. The hSensor platform is also flexible to accommodate our newer solutions in design, or on the roadmap.

　　The hSensor platform supports the measurement of motion, precision skin temperature, and a variety of biopotential measurements, including electrocardiography (ECG), electromyography (EMG), and electroencephalography (EEG). In addition, the hSensor platform also supports a variety of reflective photo plethysmography measurements including pulse oximetry and heart-rate (HR) detection at three wavelengths, 880nm (infrared, IR), 660nm (red) and 537nm (green).

　　图4.MAXREFDES100#健康传感器(hSensor)平台外形图

　　The platform supports GUI applications on Windows®-based PCs and Android®-based devices for simple data collection and visualization. Both direct USB connection (through a USB type C connector) and Bluetooth® low energy (BLE) radio are supported for configuration and data collections.

　　A direct-to-flash memory mode is supported for data collection. Flash memory read using a USB connection is also implemented.

　　The microcontroller of the platform is programmed with firmware that manages the system, controls the registers of all the devices on the platform, and communicates with the PC GUI. For users who want to customize the firmware for the microcontroller, refer to the firmware development guide for details: mbed (referenced as MAX32620HSP).

　　The following items are included in the reference design box:

　　MAXREFDES100# board: the health-sensor board

　　MAXREFDES100HDK# board: the development board for the MAXREFDES100# sensor board

　　Battery holder: for the installation of CR2032-type coin-cell battery if a USB cable is not used

　　Two ECG cables: users can solder these two ECG cables to the board for ECG measurements

　　USB type-C cable: for the connection between a PC and the MAXREFDES100# board

　　Micro-USB cable: for the connection between a PC and the MAXREFDES100HDK# board

　　The following use cases can be evaluated using this platform:

　　Fitness Applications

　　Chest-based applications

　　Chest straps with HR

　　Chest straps with HR & ECG

　　Wrist-based applications

　　Smart watches with Optical HR

　　Ear-based applications

　　Headphones with Optical HR

　　Clinical applications

　　Chest-based applications

　　1 lead-ECG patch for Arrhythmia detection (ECG & HR only)

　　Skin temperature measurements

　　Finger-based applications

　　Optical SpO2 measurement

　　Ear-based applications

　　Optical HR & SpO2

　　Head-based applications

　　Optical HR & SpO2

　　Arm-based applications

　　Arm bands with ECG

　　As with all Maxim reference designs, the bill of materials (BOM), schematics, layout files, Gerber files, firmware, and software are all available online.

　　System Diagram

　　图5. MAXREFDES100#参考设计框图

　　MAXREFDES100#参考设计硬件描述:

　　The MAX32620 microcontroller lies at the center of the hSensor. The following sensors are installed: MAX30003biopotential analog front-end (AFE), MAX30205 human body temperature sensor, MAX30101 pulse oximeter and heart-rate sensor, LIS2DH 3-axis accelerometer, LSM6DS3 3D accelerometer and 3D gyroscope, and BMP280 absolute barometric pressure sensor.

　　Power Supplies

　　The hSensor platform can be powered by a USB connection or by a CR2032-type coin cell battery. When both USB and coin cell are attached the power is drawn from the USB due to MOSFET / Schottky diode at Q4. If a coin cell is attached without USB the coin cell is used to power the hSensor platform.

　　The hSensor platform uses a MAX14720 PMIC for the majority of the power management. The PMIC has internal programming such that a 3-second button press at SW1 turns the device on. A 20-second press at SW2 turns the PMIC off.

　　The PMIC has a power-on configuration that provides 1.2V, 1.8V and VSYS voltages. Here VSYS comes from SWOUT, which in turn comes from the battery or USB through the PMIC pin SWIN. After power-up, the microcontroller configures the PMIC for a boost voltage of 3.3V, which appears at the HVOUT pin.

　　While the PMIC provides the majority of power management there are some additional power supply chips. The temperature sensors are powered by a MAX8880 LDO, which is powered by HVOUT (3.3V) and regulates this down to 2.5V. The PMIC itself is fed by a MAX8881 3.3V LDO when the hSensor is attached to USB.

　　ESD protection is provided by the MAX3205, which attaches to all of the USB signals except for DP/DM, which have ESD protection provided by the MAX32620.

　　MAXREFDES100#参考设计材料清单: