Circuit Note CN-0274 Devices Connected/Referenced Circuits from the Lab reference circuits are engineered and Nanopower, 3-Axis, 2 g, 4 g, and 8 g tested for quick and easy system integration to help solve todays ADXL362 Digital Output MEMS Accelerometer analog, mixed-signal, and RF design challenges. For more Logic Controlled, High-Side Power Switch information and/or support, visit www.analog.com/CN0274. ADP195 with Reverse Current Blocking Ultralow Power, 3-Axis, Motion Activated Switch The ADXL362 is an ultralow power, 3-axis accelerometer EVALUATION AND DESIGN SUPPORT that consumes less than 100 nA in wake-up mode. Unlike Circuit Evaluation Boards accelerometers that use power duty cycling to achieve low power CN-0274 Circuit Evaluation Board (EVAL-CN0274-SDPZ) consumption, the ADXL362 does not alias input signals by under System Demonstration Platform (EVAL-SDP-CS1Z) sampling it samples continuously at all data rates. There is also Design and Integration Files an on-chip, 12-bit temperature sensor accurate to 0.5. Schematics, Layout Files, Bill of Materials The ADXL362 provides 12-bit output resolution and has three CIRCUIT FUNCTION AND BENEFITS operating ranges, 2 g, 4 g, and 8 g. It is specified over a The combination of parts shown in Figure 1 provides an ultralow minimum temperature range of 40C to +85C. For applications power, 3-axis, motion activated power switch solution capable of where a noise level less than 480 g/Hz is desired, either of its controlling up to 1.1 A of load current. The circuit is ideal for two lower noise modes (down to 120 g/Hz) can be selected at applications where extended battery life is critical. When the switch is a minimal increase in supply current. off, the battery current is less than 300 nA, and when the switch is on, The ADP195 is a high-side load switch designed for operation it draws less than 3 A. The circuit provides an industry leading, between 1.1 V and 3.6 V and is protected against reverse current low power motion sensing solution suitable for wireless sensors, flow from output to input. The device contains a low on-resistance, metering devices, home healthcare, and other portable applications. P-channel MOSFET that supports over 1.1 A of continuous load The 3-axis accelerometer controls the high-side switch by current and minimizes power losses. monitoring the acceleration in three axes and closes or opens the switch depending on the presence or absence of motion. 3.3V 3.3V C C S IO V V S DD I/O ADXL362 MOSI INTERRUPT MISO INT1 SPI CONTROL SCLK INTERFACE INT2 GND CS AWAKE REVERSE ADP195 POLARITY PROTECTION VOUT VIN VS GND LEVEL SHIFT LOAD EN AND SLEW RATE CONTROL Figure 1. Ultralow Power Standalone Motion Switch (Simplified Schematic: Decoupling and All Connections Not Shown) Rev. A Circuits from the Lab circuits from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices Tel: 781.329.4700 www.analog.com be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) Fax: 781.461.3113 2012 Analog Devices, Inc. All rights reserved. 10773-001CN-0274 Circuit Note Basic Operation of the ADXL362 Power/Noise Tradeoff The ADXL362 is a three-axis, ultralow power acceleration The ADXL362 offers a few options for decreasing noise at the measurement system capable of measuring dynamic acceleration expense of only a small increase in current consumption. (resulting from motion or shock) as well as static acceleration The noise performance of the ADXL362 in normal operation, (that is, gravity). typically 7 LSB rms at 100 Hz bandwidth, is adequate for most The moving component of the sensor is a polysilicon, surface applications, depending upon bandwidth and the desired micromachined structure, also referred to as a beam, built on resolution. For cases where lower noise is needed, the ADXL362 top of a silicon wafer. Polysilicon springs suspend the structure provides two lower noise, operating modes that trade reduced over the surface of the wafer and provide a resistance against noise for somewhat higher supply current. acceleration forces. Table 1. ADXL362 Noise vs. Supply Current Deflection of the structure is measured using differential Noise Current Consumption capacitors. Each capacitor consists of independent fixed plates Mode (g/Hz Typical) (A Typical) and plates attached to the moving mass. Any acceleration deflects Normal Operation 380 2.7 the beam and unbalances the differential capacitor, resulting in Low Noise 280 4.5 a sensor output whose amplitude is proportional to acceleration. Ultralow Noise 175 15 Phase-sensitive demodulation is used to determine the magnitude Table 1 shows the supply current values and noise densities and polarity of the acceleration. obtained for normal operation and the two lower noise modes, Modes of Operation at a typical 3.3 V supply. The three basic modes of operation for the ADXL362 are The CN0274 evaluation software uses the normal operation standby, measurement, and wake-up. noise mode of the ADXL362. Placing the ADXL362 in standby mode suspends measurement Motion Detection and reduces current consumption to 10 nA. Any pending data The ADXL362 has built-in logic that detects activity (acceleration or interrupts are preserved however, no new information above a certain threshold) and inactivity (lack of acceleration is processed. The ADXL362 powers up in standby mode above a certain threshold). with all sensor functions turned off. Detection of an activity or inactivity event is indicated in the Measurement mode is the normal operating mode of the status register and can also be configured to generate an interrupt. ADXL362. In this mode, acceleration data is continuously In addition, the activity status of the device, that is, whether it is read, and the accelerometer consumes less than 3 A across moving or stationary, is indicated by the AWAKE bit. its entire range of output data rates of up to 400 Hz using a 2.0 V supply. All described features are available while Activity and inactivity detection can be used when the operating in this mode. The ability to continuously output accelerometer is in either measurement mode or wake-up mode. data from the minimum 12.5 Hz to the maximum 400 Hz data rate while still delivering less than 3 A 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. Rev. A Page 2 of 6