Wearable Health Monitor

The ADPD4100/ADPD4101 operate as a complete multimodal sensor front end, stimulating up to eight light emitting diodes (LEDs) and measuring the return signal on up to eight separate current inputs. Twelve time slots are available, enabling 12 separate measurements per sampling period.

The data output and functional configuration utilize an I²C interface on the ADPD4101 or a serial port interface (SPI) on the ADPD4100. The control circuitry includes flexible LED signaling and synchronous detection. The devices use a 1.8 V analog core and 1.8 V/3.3 V compatible digital input/output (I/O).

The analog front end (AFE) rejects signal offsets and corruption from asynchronous modulated interference, typically from ambient light, eliminating the need for optical filters or externally controlled dc cancellation circuitry. Multiple operating modes are provided, enabling the ADPD4100/ADPD4101 to be a sensor hub for synchronous measurements of photodiodes, biopotential electrodes, resistance, capacitance, and temperature sensors. The multiple operation modes accommodate various sensor measurements, including, but not limited to, photoplethysmography (PPG), electrocardiography (ECG), electrodermal activity (EDA), impedance, capacitance, temperature, gas detection, smoke detection, and aerosol detection for various healthcare, industrial, and consumer applications.

The ADPD4100/ADPD4101 are available in a 3.11 mm × 2.14 mm, 0.4 mm pitch, 33-ball WLCSP and 35-ball WLCSP

Applications

• Wearable health and fitness monitors: heart rate monitors (HRMs), heart rate variability (HRV), stress, blood pressure estimation, SpO2, hydration, body composition
• Industrial monitoring: CO, CO2, smoke, and aerosol detection
• Home patient monitoring

The ADPD4100/ADPD4101 operate as a complete multimodal sensor front end, stimulating up to eight light emitting diodes (LEDs) and measuring the return signal on up to eight separate current inputs. Twelve time slots are available, enabling 12 separate measurements per sampling period.

The data output and functional configuration utilize an I²C interface on the ADPD4101 or a serial port interface (SPI) on the ADPD4100. The control circuitry includes flexible LED signaling and synchronous detection. The devices use a 1.8 V analog core and 1.8 V/3.3 V compatible digital input/output (I/O).

The analog front end (AFE) rejects signal offsets and corruption from asynchronous modulated interference, typically from ambient light, eliminating the need for optical filters or externally controlled dc cancellation circuitry. Multiple operating modes are provided, enabling the ADPD4100/ADPD4101 to be a sensor hub for synchronous measurements of photodiodes, biopotential electrodes, resistance, capacitance, and temperature sensors. The multiple operation modes accommodate various sensor measurements, including, but not limited to, photoplethysmography (PPG), electrocardiography (ECG), electrodermal activity (EDA), impedance, capacitance, temperature, gas detection, smoke detection, and aerosol detection for various healthcare, industrial, and consumer applications.

The ADPD4100/ADPD4101 are available in a 3.11 mm × 2.14 mm, 0.4 mm pitch, 33-ball WLCSP and 35-ball WLCSP

Applications

• Wearable health and fitness monitors: heart rate monitors (HRMs), heart rate variability (HRV), stress, blood pressure estimation, SpO2, hydration, body composition
• Industrial monitoring: CO, CO2, smoke, and aerosol detection
• Home patient monitoring

The AD8233 is an integrated signal conditioning block for electrocardiogram (ECG) and other biopotential measurement applications. It is designed to extract, amplify, and filter small biopotential signals in the presence of noisy conditions, such as those created by motion or remote electrode placement. This design allows an ultralow power analog-to-digital converter (ADC) or an embedded microcontroller to easily acquire the output signal.

The AD8233 implements a two-pole, high-pass filter for eliminating motion artifacts and the electrode half cell potential. This filter is tightly coupled with the instrumentation amplifier architecture to allow both large gain and high-pass filtering in a single stage, thereby saving space and cost.

An uncommitted operational amplifier enables the AD8233 to create a three-pole, low-pass filter to remove additional noise. The user can select the frequency cutoff of all filters to suit different types of applications.

To improve the common-mode rejection of the line frequencies in the system and other undesired interferences, the AD8233 includes a right leg drive (RLD) amplifier for driven electrode applications. The AD8233 includes a fast restore function that reduces the duration of the otherwise long settling tails of the high-pass filters. After an abrupt signal change that rails the amplifier (such as a leads off condition), the AD8233 automatically adjusts to a higher filter cutoff. This feature allows the AD8233 to recover quickly, and therefore, to take valid measurements soon after connecting the electrodes to the subject.

The AD8233 is available in a 2 mm × 1.7 mm, 20-ball WLCSP package and a 150 μm thin die for height constrained applications. Performance is specified from 0°C to 70°C and is operational from −40°C to +85°C.

Applications

• Fitness and activity heart rate monitors
• Portable ECG
• Wearable and remote health monitors
• Gaming peripherals
• Biopotential signal acquisition, such as EMG or EEG

The ADF7030 is a low power, high performance, integrated radio transceiver supporting narrowband operation in the 169.4MHz to 169.6MHz ISM bands. The ADF7030 supports transmit and receive operation at 2.4kbps and 4.8kbps using 2GFSK modulation and transmit operation at 6.4kbps using 4GFSK modulation.

The ADF7030 features an on-chip ARM^® Cortex^®-M0 processor that performs radio control and packet management.

• Wireless M-Bus Mode N (EN 13757-4)
• Smart metering
• Social alarms
• Active tag asset tracking

The ADF7030-1 is a fully integrated, radio transceiver achieving high performance at very low power. The ADF7030-1 is ideally suited for applications that require long range, network robustness, and long battery life. It is suitable for applications that operate in the ISM, SRD, and licensed frequency bands at 169.4 MHz to 169.6 MHz, 426 MHz to 470 MHz, and 863 MHz to 960 MHz. It provides extensive support for standards-based protocols like IEEE802.15.4g while also providing flexibility to support a wide range of proprietary protocols.

The highly configurable low intermediate frequency (IF) receiver supports a large range of receiver channel bandwidths from 2.6 kHz to 406 kHz. This range of receiver channel bandwidths allows the ADF7030-1 to support ultranarrow-band, narrow-band, and wideband channel spacing.

The ADF7030-1 features two independent PAs supporting output power ranges of −20 dBm to +13 dBm and −20 dBm to +17 dBm. The PAs support ultrafine adjustment of the power with a step resolution of 0.1 dB. The PA output power is exceptionally robust over temperature and voltage. The PAs have an automatic power ramp control to limit spectral splatter to meet regulatory standards.

The ADF7030-1 features an on-chip ARM^® Cortex^®-M0 processor that performs radio control, radio calibration, and packet management. Cortex-M0 eases the processing burden of the host processor because the ADF7030-1 integrates the lower layers of a typical communication protocol stack. This internal processor also permits the download and execution of Analog Devices, Inc., provided firmware modules that can extend the functionality of the ADF7030-1.

The ADF7030-1 has two packet modes: generic packet mode and IEEE802.15.4g mode. In generic packet mode, the packet format is highly flexible and fully programmable, thereby ensuring its compatibility with proprietary packet formats. In IEEE802.15.4g packet mode, the packet format conforms to the IEEE802.15.4g standard. FEC, as per the IEEE802.15.4g standard, is also supported.

The ADF7030-1 operates with a power supply range of 2.2 V to 3.6 V and has very low power consumption in both Tx and Rx modes, enabling long lifetimes in battery-operated systems. An ultralow power deep sleep mode achieves a typical current of 10 nA with the configuration memory retained.

A complete wireless solution can be built using a small number of external discrete components and a host processor (typically a microcontroller). The host processor can configure the ADF7030-1 using a simple command-based protocol over a standard 4-wire SPI interface. A single-byte command transitions the radio between states or performs a radio function.

The ADF7030-1 is available in two package types: a 6 mm × 6 mm, 40-lead LFCSP and a 7 mm × 7 mm, 48-lead LQFP. Both package types use NiPdAu plating to mitigate against silver migration in high humidity applications. The ADF7030-1 operating temperature range is −40°C to +85°C.

For Figure 13 to Figure 19, Figure 30, Figure 42, Figure 60, Figure 61, and Figure 75 in the Typical Performance Characteristics section, PA_COARSE is a programmable value that provides a coarse adjustment of the PA output power. This value can be programmed in the range of 1 to 6 for PA1, and from 1 to 10 for PA2. PA_FINE is a programmable value that provides a fine adjustment of the PA output power. This value can be programmed in the range of 3 to 127 for both PA1 and PA2. PA_MICRO is a programmable value that provides a microadjustment (typically <0.1 dB) of the PA output power. This value can be programmed in the range of 1 to 31 for both PA1 and PA2. PAOLDO_VOUT_CON is a programmable value that configures the internal LDO voltage that provides bias for the PA. For additional information on these bit settings, see the ADF7030-1 Software Reference Manual, which is the detailed programming guide for the device.

Applications

• IEEE 802.15.4g (MR-FSK PHY) 
• Wireless M-Bus (EN 13757-4)
• Smart metering
• Security and building automation 
• Active tag asset tracking
• Industrial control
• Wireless sensor networks (WSNs)

The ADP5301 is a high efficiency, ultralow quiescent current step-down regulator that draws only a 180 nA quiescent current to regulate the output at no load.

The ADP5301 runs from an input startup voltage range of 2.15 V to 6.50 V, allowing the use of multiple alkaline/NiMH, Li-Ion cells, or other power sources. The output voltage is selectable from 0.8 V to 5.0 V by an external VID resistor and factory fuse. The total solution requires only four tiny external components.

The ADP5301 can operate between hysteresis mode and PWM mode via the SYNC/MODE pin. The regulator in hysteresis mode achieves excellent efficiency at a power of less than 1 mW and provides up to 50 mA of output current. The regulator in PWM mode produces a lower output ripple and supplies up to 500 mA of output current. The flexible configuration capability during operation of the device enables very efficient power management to meet both the longest battery life and low system noise requirements.

The ADP5301 contains a VOUTOK flag, which monitors the output voltage and runs at a 2 MHz switching frequency in PWM mode. SYNC/MODE can synchronize to an external clock from 1.5 MHz to 2.5 MHz.

Other key features in the ADP5301 include separate enabling, quick output discharge (QOD), and safety features such as overcurrent protection (OCP), thermal shutdown (TSD), and input undervoltage lockout (UVLO).

The ADP5301 is available in a 9-ball, 1.65 mm × 1.87 mm WLCSP rated for a −40°C to +125°C junction temperature range.

Applications

• Energy (gas and water) metering
• Portable and battery-powered equipment
• Medical applications
• Keep-alive power supplies

The ADPD105/ADPD106/ADPD107 are highly efficient, photometric front ends, each with an integrated 14-bit analog-to-digital converter (ADC) and a 20-bit burst accumulator that works with flexible light emitting diode (LED) drivers. The accumulator is designed to stimulate an LED and measure the corresponding optical return signal. The data output and functional configuration occur over a 1.8 V I²C interface on the ADPD105 or SPI on the ADPD106 and ADPD107. The control circuitry includes flexible LED signaling and synchronous detection.

The analog front end (AFE) features best-in-class rejection of signal offset and corruption due to modulated interference commonly caused by ambient light.

Couple the ADPD105/ADPD106/ADPD107 with a low capacitance photodiode of <100 pF for optimal performance. The ADPD105/ADPD106/ADPD107 can be used with any LED. The ADPD105 is available in a 2.46 mm × 1.4 mm WLCSP and a 4 mm × 4 mm LFCSP. The SPI only versions, ADPD106 and ADPD107, are available in a 2.46 mm × 1.4 mm WLCSP.

Applications

• Wearable health and fitness monitors
• Clinical measurements, for example, SpO₂
• Industrial monitoring
• Background light measurements

The ADPD105/ADPD106/ADPD107 are highly efficient, photometric front ends, each with an integrated 14-bit analogto-digital converter (ADC) and a 20-bit burst accumulator that works with flexible light emitting diode (LED) drivers. The accumulator is designed to stimulate an LED and measure the corresponding optical return signal. The data output and functional configuration occur over a 1.8 V I²C interface on the ADPD105 or SPI on the ADPD106 and ADPD107. The control circuitry includes flexible LED signaling and synchronous detection.

The analog front end (AFE) features best-in-class rejection of signal offset and corruption due to modulated interference commonly caused by ambient light.

Couple the ADPD105/ADPD106/ADPD107 with a low capacitance photodiode of <100 pF for optimal performance. The ADPD105/ADPD106/ADPD107 can be used with any LED. The ADPD105 is available in a 2.46 mm × 1.4 mm WLCSP and a 4 mm × 4 mm LFCSP. The SPI only versions, ADPD106 and ADPD107, are available in a 2.46 mm × 1.4 mm WLCSP.

Applications

• Wearable health and fitness monitors
• Clinical measurements, for example, SpO₂
• Industrial monitoring
• Background light measurements

The ADPD105/ADPD106/ADPD107 are highly efficient, photometric front ends, each with an integrated 14-bit analog-to-digital converter (ADC) and a 20-bit burst accumulator that works with flexible light emitting diode (LED) drivers. The accumulator is designed to stimulate an LED and measure the corresponding optical return signal. The data output and functional configuration occur over a 1.8 V I²C interface on the ADPD105 or SPI on the ADPD106 and ADPD107. The control circuitry includes flexible LED signaling and synchronous detection.

The analog front end (AFE) features best-in-class rejection of signal offset and corruption due to modulated interference commonly caused by ambient light.

Couple the ADPD105/ADPD106/ADPD107 with a low capacitance photodiode of <100 pF for optimal performance. The ADPD105/ADPD106/ADPD107 can be used with any LED. The ADPD105 is available in a 2.46 mm × 1.4 mm WLCSP and a 4 mm × 4 mm LFCSP. The SPI only versions, ADPD106 and ADPD107, are available in a 2.46 mm × 1.4 mm WLCSP.

Applications

• Wearable health and fitness monitors
• Clinical measurements, for example, SpO₂
• Industrial monitoring
• Background light measurements

The ADuCM3027/ADuCM3029 microcontroller units (MCUs) are ultra low power microcontroller systems with integrated power management for processing, control, and connectivity. The MCU system is based on the ARM^® Cortex^®-M3 processor, a collection of digital peripherals, embedded SRAM and flash memory, and an analog subsystem which provides clocking, reset, and power management capability in addition to an analog-to-digital converter (ADC) subsystem. For a feature comparison across the ADuCM3027/ADuCM3029 product offerings, see Table 1.

System features that are common across the ADuCM3027/ADuCM3029/ADuCM3029-1/ADuCM3029-2 MCUs include the following:

• Up to 26 MHz ARM Cortex-M3 processor
• Up to 256 kB of embedded flash memory with error correction code (ECC)
• Optional 4 kB cache for lower active power
• 64 kB system SRAM with parity
• Power management unit (PMU)
• Multilayer advanced microcontroller bus architecture (AMBA) bus matrix
• Central direct memory access (DMA) controller
• Beeper interface
• Serial port (SPORT), serial peripheral interface (SPI), inter-integrated circuit (I²C), and universal asynchronous receiver/transmitter (UART) peripheral interfaces
• Cryptographic hardware support with advanced encryption standard (AES) and secure hash algorithm (SHA)-256
• Real-time clock (RTC)
• General-purpose and watchdog timers
• Programmable general-purpose input/output (GPIO) pins
• Hardware cyclic redundancy check (CRC) calculator with programmable generator polynomial
• Power-on reset (POR) and power supply monitor (PSM)
• 12-bit successive approximation register (SAR) ADC
• True random number generator (TRNG)

To support low dynamic and hibernate power management, the ADuCM3027/ADuCM3029 MCUs provide a collection of power modes and features, such as dynamic and software controlled clock gating and power gating.

The ADuCM3029-1 and ADuCM3029-2 MCU models share the same features and functionality as that of the ADuCM3029 MCU. All specifications pertaining to the ADuCM3027 and ADuCM3029 are also applicable to the ADuCM3029-1 and ADuCM3029-2.

For full details on the ADuCM3027/ADuCM3029 MCUs, refer to the ADuCM302x Ultra Low Power ARM Cortex-M3 MCU with Integrated Power Management Hardware Reference Manual.

Product Highlights

1. Industry leading ultralow power consumption.
2. Robust operation, including full voltage monitoring in deep sleep modes, ECC support on flash, and parity error detection on SRAM memory.
3. Leading edge security. Fast encryption provides read protection to customer algorithms. Write protection prevents device reprogramming by unauthorized code.
4. Failure detection of 32 kHz LFXTAL via interrupt.
5. SensorStrobe^™ for precise time synchronized sampling of external sensors. Works in hibernate mode, resulting in drastic current reduction in system solutions. Current consumption reduces by 10 times when using, for example, the ADXL363 accelerometer. Software intervention is not required after setup. No pulse drift due to software execution.

Applications

• Internet of Things (IoT)
• Electronic shelf label (ESL) and signage
• Smart infrastructure
• Smart lock
• Asset tracking
• Smart machine, smart metering, smart building, smart city, and smart agriculture
• Wearables
• Fitness and clinical
• Machine learning and neural network 

The ADuCM350 is a configurable Impedance Converter and Potentiostat with current and voltage measurement capability for both Electrochemical sensors and Biosensors. It is a complete, coin cell powered, high precision, MCU integrated solution for portable device applications such as point-of-care diagnostics and body-worn devices for monitoring vital signs.

The ADuCM350 analog front end (AFE) features a 16-bit, precision, 160 kSPS analog-to-digital converter (ADC); 0.17% precision voltage reference; 12-bit, no missing codes digital-to-analog converter (DAC); and a reconfigurable ultralow leakage switch matrix. It has 4 voltage measurement channels, up to 8 current measurement channels and an impedance measurement DFT engine. The ADuCM350 also includes an ARM Cortex-M3-based processor, memory, and all I/O connectivity to support portable meters with display, USB communication, and active sensors. The ADuCM350 is available in a 120-lead, 8 mm × 8 mm CSP_BGA and operates from −40°C to +85°C.

To support extremely low dynamic and hibernate power management, the ADuCM350 provides a collection of power modes and features, such as dynamic and software controlled clock gating and power gating. The AFE is connected to the ARM Cortex-M3 via an advanced high performance bus (AHPB) slave interface on the advanced microcontroller bus architecture (AMBA) matrix, as well as direct memory access (DMA) and interrupt connections.

APPLICATIONS

• Point-of-care diagnostics
• Body-worn devices for monitoring vital signs
• Amperometric, voltametric, and impedometric measurements

The analog output ADXL354 and the digital output ADXL355 are low noise density, low 0 g offset drift, low power, 3-axis accelerometers with selectable measurement ranges. The ADXL354B supports the ±2 g and ±4 g ranges, the ADXL354C supports the ±2 g and ±8 g ranges, and the ADXL355 supports the ±2 g, ±4 g, and ±8 g ranges. The ADXL354/ADXL355 offer industry leading noise, minimal offset drift over temperature, and long-term stability enabling precision applications with minimal calibration.

Highly integrated in a compact form factor, the low power ADXL355 is ideal in an Internet of Things (IoT) sensor node and other wireless product designs.

The ADXL355 multifunction pin names may be referenced by their relevant function only for either the serial peripheral interface (SPI) or I²C interface.

Applications

• Inertial measurement units (IMUs)/altitude and heading reference systems (AHRS)
• Platform stabilization systems
• Structural health monitoring
• Seismic imaging
• Tilt sensing
• Robotics
• Condition Monitoring

The analog output ADXL354 and the digital output ADXL355 are low noise density, low 0 g offset drift, low power, 3-axis accelerometers with selectable measurement ranges. The ADXL354B supports the ±2 g and ±4 g ranges, the ADXL354C supports the ±2 g and ±8 g ranges, and the ADXL355 supports the ±2 g, ±4 g, and ±8 g ranges. The ADXL354/ADXL355 offer industry leading noise, minimal offset drift over temperature, and long-term stability enabling precision applications with minimal calibration.

Highly integrated in a compact form factor, the low power ADXL355 is ideal in an Internet of Things (IoT) sensor node and other wireless product designs.

The ADXL355 multifunction pin names may be referenced by their relevant function only for either the serial peripheral interface (SPI) or I²C interface.

Applications

• Inertial measurement units (IMUs)/altitude and heading reference systems (AHRS)
• Platform stabilization systems
• Structural health monitoring
• Seismic imaging
• Tilt sensing
• Robotics
• Condition Monitoring

The ADXL362 is an ultralow power, 3-axis MEMS accelerometer that consumes less than 2 μA at a 100 Hz output data rate and 270 nA when in motion triggered wake-up mode. Unlike accelerometers that use power duty cycling to achieve low power consumption, the ADXL362 does not alias input signals by undersampling; it samples the full bandwidth of the sensor at all data rates.

The ADXL362 always provides 12-bit output resolution; 8-bit formatted data is also provided for more efficient single-byte transfers when a lower resolution is sufficient. Measurement ranges of ±2 g, ±4 g, and ±8 g are available, with a resolution of 1 mg/LSB on the ±2 g range. For applications where a noise level lower than the normal 550 μg/√Hz of the ADXL362 is desired, either of two lower noise modes (down to 175 μg/√Hz typical) can be selected at minimal increase in supply current.

In addition to its ultralow power consumption, the ADXL362 has many features to enable true system level power reduction. It includes a deep multimode output FIFO, a built-in micropower temperature sensor, and several activity detection modes including adjustable threshold sleep and wake-up operation that can run as low as 270 nA at a 6 Hz (approximate) measurement rate. A pin output is provided to directly control an external switch when activity is detected, if desired. In addition, the ADXL362 has provisions for external control of sampling time and/or an external clock.

The ADXL362 operates on a wide 1.6 V to 3.5 V supply range, and can interface, if necessary, to a host operating on a separate, lower supply voltage. The ADXL362 is available in a 3 mm × 3.25 mm × 1.06 mm package.

Applications

• Hearing aids
• Home healthcare devices
• Motion enabled power save switches
• Wireless sensors
• Motion enabled metering devices

The ADXL345 is a small, thin, low power, 3-axis accelerometer with high resolution (13-bit) measurement up to ±16 g. Digital output data is formatted as 16-bit twos complement and is accessible through either an SPI (3- or 4-wire) or I²C digital interface.

The ADXL345 is well suited for mobile device applications. It measures the static acceleration of gravity in tilt-sensing appli-cations, as well as dynamic acceleration resulting from motion or shock. Its high resolution (4 mg/LSB) enables measurement of inclination changes of about 0.25°. Using a digital output accelerometer such as the ADXL345 eliminates the need for analog-to-digital conversion, reducing system cost and real estate. Additionally, the ADXL345 includes a variety of built-in features. Activity/inactivity detection, tap/double-tap detection, and free-fall detection are all done internally with no need for the host processor to perform any calculations. A built-in 32-stage FIFO memory buffer reduces the burden on the host processor, allowing algorithm simplification and power savings. Additional system level power savings can be implemented using the built-in activity/inactivity detection and by using the ADXL345 as a “motion switch” to turn the whole system off when no activity is felt and on when activity is sensed again.

The ADXL345 communicates via I²C or SPI interface. The circuits described in this document demonstrate how to implement communication via these protocols.

The universal serial bus (USB) is rapidly becoming the standard interface for most PC peripherals. It is displacing RS-232 and the parallel printer port because of superior speed, flexibility, and support of device hot swap. There has been a strong desire on the part of industrial and medical equipment manufacturers to use this bus as well, but adoption has been slow because there has not been a good way to provide the isolation required for connections to machines that control dangerous voltages or low leakage defibrillation proof connections in medical applications.

The ADuM4160 provides an inexpensive and easy to implement isolation buffer for medical and industrial peripherals. The challenges that need to be met are:

1. Isolate directly in the USB D+ and D− lines allowing the use of existing USB infrastructure in microprocessors.
2. Implement an automatic scheme for data flow of control that does not require external control lines.
3. Provide medical grade isolation.
4. Allow a complete peripheral to meet the USB-IF certifi-cation standards.
5. Support full speed (12 Mbps) and low speed (1.5 Mbps) signaling rates.
6. Support flexible power configurations.

The circuit shown in Figure 1 isolates a peripheral device that already supports a USB interface. Because the peripheral is not explicitly defined in this circuit, power to run the secondary side of the isolator has been provided as part of the solution. If the circuit is built onto the PCB of a peripheral design, power could be sourced from the peripheral’s off line supply, a battery, or the USB cable bus power, depending on the needs of the application.

The application circuit shown is typical of many medical and industrial applications.

The universal serial bus (USB) is rapidly becoming the standard interface for most PC peripherals. It is displacing RS-232 and the parallel printer port because of superior speed flexibility and support of device hot swap. There has been a strong desire on the part of industrial and medical equipment manufacturers to use the bus as well, but adoption has been slow because there has not been a good way to provide the isolation required for connections to machines that control dangerous voltages or low leakage defibrillation proof connections in medical applications.

The ADuM4160 is designed primarily as an isolation element for a peripheral USB device. However, there are occasions when it is useful to create an isolated cable function. Several issues must be addressed to use the ADuM4160 for this application. Whereas the buffers on the upstream and downstream sides of the ADuM4160 are the same and capable of driving a USB cable, the downstream buffers must be capable of adjusting speed to a full or low speed peripheral that is connected to it. The upstream connection must act like a peripheral, and the downstream connection must behave like a host.

Unlike the case of building a dedicated peripheral interface where the speed is known and not changed, host applications must adapt to detect whether a low or full speed device has been connected. The ADuM4160 is intended to be hardwired to a single speed via pins; therefore, it works when the peripheral plugged into its downstream side is the correct speed, but it fails when the wrong speed peripheral is attached. The best way to address this is to combine the ADuM4160 with a hub controller.

The upstream side of a hub controller can be thought of as a standard fixed speed peripheral port that can be easily isolated with the ADuM4160, whereas the downstream ports are all handled by the hub controller. However, in many cases, while it is not certifiable as fully USB compliant, a single speed cable is acceptable from a practical standpoint, especially if custom connectors are used so that it cannot be confused with a compliant device. The hub chip can be eliminated, and the design becomes very small and simple.

The ADuM4160 provides an inexpensive and easy way to implement an isolation buffer for medical and industrial peripherals. The challenge that must be met is to use this to create a bus-powered cable isolator by pairing the ADuM4160 with a small isolated dc-to-dc converter such as the ADuM5000. As with isolating any device, the services that the ADuM4160 provides are as follows:

1. Directly isolates, in the upstream, the USB D+ and D− lines of a cable.
2. Implements an automatic scheme for data flow of control that does not require external control lines.
3. Provides medical grade isolation.
4. Supports full speed or low speed signaling rates.
5. Supports isolated power delivery through the cable.

The goal of the application circuit shown in Figure 1 is to isolate a peripheral device that already implements a USB interface. It is not possible to make a fully compliant bus-powered cable because there are no 100% efficient power converters to transfer the bus voltage across the barrier. In addition, the quiescent current of the converter does not comply with the standby current requirements of the USB standard. This is all in addition to the speed detection limitations of the ADuM4160. What can be achieved is a fixed speed or switch-controlled speed cable that can supply a modest power to the downstream peripheral. However, it is a custom application that is not completely compliant with the USB standard.

The combination of parts shown in Figure 1 provides an ultralow power, 3-axis, motion activated power switch solution capable of controlling up to 1.1 A of load current. The circuit is ideal for applications where extended battery life is critical. When the switch is off, the battery current is less than 300 nA, and when the switch is on, it draws less than 3 μA. The circuit provides an industry leading, low power motion sensing solution suitable for wireless sensors, metering devices, home healthcare, and other portable applications.

The 3-axis accelerometer controls the high-side switch by monitoring the acceleration in three axes and closes or opens the switch depending on the presence or absence of motion.

The ADXL362 is an ultralow power, 3-axis accelerometer that consumes less than 100 nA in wake-up mode. Unlike accelerometers that use power duty cycling to achieve low power consumption, the ADXL362 does not alias input signals by under sampling; it samples continuously at all data rates. There is also an on-chip, 12-bit temperature sensor accurate to ±0.5°.

The ADXL362 provides 12-bit output resolution and has three operating ranges, ±2 g, ±4 g, and ±8 g. It is specified over a minimum temperature range of −40°C to +85°C. For applications where a noise level less than 480 μg/√Hz is desired, either of its two lower noise modes (down to 120 μg/√Hz) can be selected at a minimal increase in supply current.

Basic Operation of the ADXL362

The ADXL362 is a three-axis, ultralow power acceleration measurement system capable of measuring dynamic acceleration (resulting from motion or shock) as well as static acceleration (that is, gravity).

The moving component of the sensor is a polysilicon, surface micromachined structure, also referred to as a beam, built on top of a silicon wafer. Polysilicon springs suspend the structure over the surface of the wafer and provide a resistance against acceleration forces.

Deflection of the structure is measured using differential capacitors. Each capacitor consists of independent fixed plates and plates attached to the moving mass. Any acceleration deflects the beam and unbalances the differential capacitor, resulting in a sensor output whose amplitude is proportional to acceleration. Phase-sensitive demodulation is used to determine the magnitude and polarity of the acceleration.

Modes of Operation

The three basic modes of operation for the ADXL362 are standby, measurement, and wake-up.

• Placing the ADXL362 in standby mode suspends measurement and reduces current consumption to 10 nA. Any pending data or interrupts are preserved; however, no new information is processed. The ADXL362 powers up in standby mode with all sensor functions turned off.

• Measurement mode is the normal operating mode of the ADXL362. In this mode, acceleration data is continuously read, and the accelerometer consumes less than 3 μA across its entire range of output data rates of up to 400 Hz using a 2.0 V supply. All described features are available while operating in this mode. The ability to continuously output data from the minimum 12.5 Hz to the maximum 400 Hz data rate while still delivering less than 3 μA of current consumption is what defines the ADXL362, as an ultralow power accelerometer. Under sampling and aliasing do not occur with the ADXL362. because it continuously samples the full bandwidth of its sensor at all data rates.

• Wake-up mode is ideal for simple detection of the presence or absence of motion at extremely low power consumption (270 nA at a 2.0 V supply voltage). Wake-up mode is useful particularly for implementation of a motion-activated on/off switch, allowing the rest of the system to be powered down until activity is detected. Wake-up mode reduces current consumption to a very low level by measuring acceleration only 6 times a second to determine whether motion is present. In wake-up mode, all accelerometer features are available with the exception of the activity timer. All registers are accessible, and real-time data is available from the part.

The CN0274 evaluation software uses the wake-up mode of the ADXL362. That is, the ADXL362 is asleep until it detects motion at which point it enters measurement mode.

Power/Noise Tradeoff

The ADXL362 offers a few options for decreasing noise at the expense of only a small increase in current consumption.

The noise performance of the ADXL362 in normal operation, typically 7 LSB rms at 100 Hz bandwidth, is adequate for most applications, depending upon bandwidth and the desired resolution. For cases where lower noise is needed, the ADXL362 provides two lower noise, operating modes that trade reduced noise for somewhat higher supply current.

Table 1 shows the supply current values and noise densities obtained for normal operation and the two lower noise modes, at a typical 3.3 V supply.

The CN0274 evaluation software uses the normal operation noise mode of the ADXL362.

Motion Detection

The ADXL362 has built-in logic that detects activity (acceleration above a certain threshold) and inactivity (lack of acceleration above a certain threshold).

Detection of an activity or inactivity event is indicated in the status register and can also be configured to generate an interrupt. In addition, the activity status of the device, that is, whether it is moving or stationary, is indicated by the AWAKE bit.

Activity and inactivity detection can be used when the accelerometer is in either measurement mode or wake-up mode.

Activity Detection

An activity event is detected when acceleration stays above a specified threshold for a user-specified time period. The two activity detection events are absolute and referenced.

• When using absolute activity detection, acceleration samples are compared to a user set threshold to determine whether motion is present. For example, if a threshold of 0.5 g is set, and the acceleration on any axis is 1 g for longer than the user defined activity time, the activity status is asserted. In many applications, it is advantageous for activity detection to be based not on an absolute threshold but on a deviation from a reference point or orientation. This is particularly useful because it removes the effect on activity detection of the static 1 g imposed by gravity. When an accelerometer is stationary, its output can reach 1 g, even when it is not moving. In absolute activity, if the threshold is set to less than 1 g, activity is immediately detected in this case.
• In the referenced activity detection, activity is detected when acceleration samples are at least a user set amount above an internally defined reference, for the user defined amount of time. The reference is calculated when activity detection is engaged, and the first sample obtained is used as a reference point. Activity is only detected when the acceleration has deviated sufficiently from this initial orientation. The referenced configuration results in a very sensitive activity detection that detects even the most subtle motion events.

The CN0274 evaluation software uses the referenced mode of operation when searching for activity.

Inactivity Detection

An inactivity event is detected when acceleration remains below a specified threshold for a specified time. The two inactivity detection events are absolute and referenced.

• In absolute inactivity detection, acceleration samples are compared to a user set threshold for the user set time to determine the absence of motion.
• In referenced inactivity detection, acceleration samples are compared to a user specified reference for a user defined amount of time. When the part first enters the awake state, the first sample is used as a reference point, and the threshold is applied around it. If the acceleration stays inside the threshold, the part enters the asleep state. If an acceleration value moves outside the threshold, this point is then used as a new reference, and the thresholds are reapplied to this new point.

The CN0274 evaluation software uses the referenced mode of operation when searching for inactivity.

Linking Activity and Inactivity Detection

The activity and inactivity detection functions can be used concurrently, and processed manually by a host processor, or they can be configured to interact in several ways:

• In default mode, activity and inactivity detection are both enabled, and all interrupts must be serviced by a host processor; that is, a processor must read each interrupt before it is cleared and can be used again.
• In linked mode, activity and inactivity detection are linked to each other such that only one of the functions is enabled at any given time. Once activity is detected, the device is assumed moving or awake and stops looking for activity: inactivity is expected as the next event so only inactivity detection operates. When inactivity is detected, the device is assumed stationary or asleep. Activity is now expected as the next event so that only activity detection operates. In this mode, a host processor must service each interrupt before the next is enabled.
• In loop mode, motion detection operates as previously described in linked mode; however, interrupts do not need to be serviced by a host processor. This configuration simplifies the implementation of commonly used motion detection and enhances power savings by reducing the amount of power used in bus communication.
• When enabling autosleep mode in linked mode or loop mode, it causes the device to autonomously enter wake-up mode when inactivity is detected, and reenter measurement mode when activity is detected.

The CN0274 evaluation software uses the autosleep and loop modes to demonstrate the functionality of the ADXL362.

The AWAKE Bit

The AWAKE bit is a status bit that indicates whether the ADXL362 is awake or asleep. The device is awake when it has seen an activity condition, and the device is asleep when it has seen an inactivity condition.

The awake signal can be mapped to the INT1 or INT2 pin and can thus be used as a status output to connect or disconnect power to downstream circuitry based on the awake status of the accelerometer. Used in conjunction with loop mode, this configuration implements a trivial, autonomous motion-activated switch.

If the turn-on time of the downstream circuitry can be tolerated, this motion switch configuration can save significant system-level power by eliminating the standby current consumption of the rest of the application. This standby current can often exceed the full operating current of the ADXL362.

Interrupts

Several of the built-in functions of the ADXL362 can trigger interrupts to alert the host processor of certain status conditions.

Interrupts may be mapped to either (or both) of two designated output pins, INT1 and INT2, by setting the appropriate bits in the INTMAP1 and INTMAP2 registers. All functions can be used simultaneously. If multiple interrupts are mapped to one pin, the OR combination of the interrupts determines the status of the pin.

If no functions are mapped to an interrupt pin, that pin is automatically configured to a high impedance (high-Z) state. The pins are placed in this state upon a reset as well.

When a certain status condition is detected, the pin that condition is mapped to is activated. The configuration of the pin is active high by default, so that when it is activated, the pin goes high. However, this configuration can be switched to active low by setting the INT_LOW pin in the appropriate INTMAP register.

The INT pins may be connected to the interrupt input of a host processor and interrupts responded to with an interrupt routine. Because multiple functions can be mapped to the same pin, the STATUS register can be used to determine which condition caused the interrupt to trigger.

The CN0274 evaluation software configures the ADXL362 such that when activity is detected, the INT1 pin is high, and when inactivity is detected, the INT1 pin is low.

Test Results

All testing was performed using the EVAL-CN0274-SDPZ and the EVAL-SDP-CS1Z. Functionality of the part is demonstrated by setting the activity threshold at 0.5 g, the inactivity threshold at 0.75 g, and the number of inactivity samples at 20. When looking for activity, only one acceleration sample on any axis is required to cross the threshold.

Starting with the circuit oriented so that the battery pack is flat against the table, the printed circuit board (PCB) can be slowly rotated 90° in any direction causing the acceleration to cross the threshold as it approaches perpendicular to the initial orientation.

Figure 2 shows a screen shot of the CN0274 evaluation software showing the ADXL362 first asleep, looking for activity. Then, when Sample 11 crosses the threshold, the ADXL362 enters the awake state and begins looking for inactivity. The thresholds adjust to show the device is now looking for inactivity.

For better visibility, the X-axis and Z-axis plots are disabled using the radio buttons above the chart.

The output of the ADP195, or the interrupt pin itself, was measured using a digital multimeter. When the ADXL362 is awake, the interrupt goes high and drives the EN pin of the ADP195, high, which in turn drives the gate of the MOSFET low, causing the switch to close, connecting any downstream circuitry to the power supply. Conversely, when the ADXL362 is asleep, the interrupt drives the EN pin of the ADP195 low, which in turn drives the gate of the MOSFET high, causing the switch to open.

PCB Layout Considerations

In any circuit where accuracy is crucial, it is important to consider the power supply and ground return layout on the board. The PCB should isolate the digital and analog sections as much as possible. The PCB for this system was constructed in a 4-layer stack up with large area ground plane layers and power plane polygons. See the MT-031 Tutorial for more discussion on layout and grounding, and the MT-101 Tutorial for information on decoupling techniques.

Decouple the power supply to the ADXL362 with 1 μF and 0.1 μF capacitors to properly suppress noise and reduce ripple. Place the capacitors as close to the device as possible. Ceramic capacitors are advised for all high frequency decoupling.

Power supply lines should have as large a trace width as possible to provide low impedance paths and reduce glitch effects on the supply line. Shield clocks and other fast switching digital signals from other parts of the board by digital ground. A photo of the PCB is shown in Figure 3.

A complete design support package for this circuit note can be found at www.analog.com/CN0274-DesignSupport.