Circuit Note CN-0532 Devices Connected/Referenced Circuits from the Lab reference designs are engineered Low Noise, High Frequency MEMS and tested for quick and easy system integration to help solve ADXL1002 Accelerometer todays analog, mixed-signal, and RF design challenges. For more information and/or support, visit General-Purpose CMOS Single Rail-to- www.analog.com/CN0532. AD8541 Rail Amplifier IEPE-Compatible Interface for Wideband MEMS Accelerometer Sensors With recent advancements in the microtechnology processes EVALUATION AND DESIGN SUPPORT and fabrication techniques, MEMS accelerometers have caught Circuit Evaluation Boards up with piezoelectric sensors low noise levels and supersede in CN-0532 Circuit Evaluation Board (EVAL-CN0532-EBZ) other many specifications, such as dc to low frequency Aluminum mounting block (EVAL-XLMOUNT1) response, thermal stability, shock resistance and recovery, and Design and Integration Files cost. The output of MEMS sensors, however, are either Schematics, Layout Files, Bill of Materials conventional 3-wire analog (ground, power, and signal) or CIRCUIT FUNCTION AND BENEFITS digital if integrated with an ADC. Neither output are directly compatible with IEPE, the preferred CbM industry sensor Condition-based monitoring (CbM) is one form of predictive interface. maintenance that uses sensors to assess status of equipment overtime while the equipment is operating. The collected sensor This reference design enables a direct piezoelectric sensor IEPE data can establish baseline trends, such as, diagnose or even replacement with benefits of high bandwidth, ultralow noise predict failure. Utilizing CbM, maintenance is performed when MEMS accelerometers. This circuit allows customers to easily needed as opposed to the conventional periodic preventive evaluate a MEMS accelerometer for CbM applications. maintenance model, saving both time and money. Vibration monitoring is a common type of CbM measurement because changes in vibration trends are potentially indicative of wear or other failure modes. To measure vibration data, high bandwidth (10 kHz and more), ultralow noise (100 g/Hz or lower) piezoelectric sensors were historically used to satisfy these requirements. The established sensor interface for piezo sensors is integrated electronics piezoelectric (IEPE), as a result, IEPE has become a de facto interface in CbM vibration ecosystem. Rev. 0 Circuits from the Lab reference designs 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. determining its suitability and applicability for your use and application. Accordingly, in no event shall Tel: 781.329.4700 www.analog.com Analog Devices 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 2020 Analog Devices, Inc. All rights reserved. CN-0532 Circuit Note V DD IC1 TLVH432 V DD V R3 R1 REF R2 IC2 3. 3k 51k 150k ADXL1002 OR OR C1 10F ST R4 V IEPE 470k IC4 ST TLVH432 STB V R5 DD 470k R10 R11 STDBY V REF 36k 100k R6 R8 680 1. 3k IC3 V OUT AD8541 C4 C5 C8 4.7nF 4.7nF 10F Figure 1. Complete ADXL1002 with IEPE Compatible Circuit Diagram Figure 3 shows the basic operation of the circuit. Regulator A CIRCUIT DESCRIPTION supplies current to all elements. Regulator B adds dc offset The circuit shown in Figure 1 demonstrates a MEMS (approximately 9.5 V) to the buffered output of the ADXL1002 accelerometer vibration sensing solution with included IEPE- (2.5 V 2 V) which gives enough compliance to the signal line compatible interface circuitry at 12.5 V bias and 4 mA current (output voltage (V IEPE) = 12 V 2 V). Because the voltage consumption. level on the signal line is always higher than 5 V, the shunt IEPE Protocol and Interface regulator (Regulator A) can generate a stable VDD (5 V) to The IEPE interface is a 2-wire protocol, signal and ground. An power both the ADXL1002 and the AD8541. instrument, such as data logger, supplies power via the signal 4mA line to the vibration sensor as current with an arbitrary voltage, V IEPE 12V 2V typically between 10 V to 30 V. Because the signal line is R3 5V REGULATOR B supplied by a current source, the sensor device can modulate 9.5V the acceleration data on the voltage rail. Therefore, the single wire can be used for both the power supply and the modulated 2.5V 2V ADXL1002 REGULATOR A V OUT 5V output voltage of the sensor. Figure 2 shows an example of the IEPE output with a bias voltage of 12 V and a full-scale range (FSR) swing of 2 V. Figure 3. Simplified Schematic of the IEPE Interface, 4 mA Current Consumption at a 12 V Bias Voltage The signal line current must not exceed 4 mA (the most common industry norm) and supply enough current to power 14 the shunt regulators, buffer amplifier, and sensors for the whole FSR BIAS SWING sensor output swing, which is the primary constraint when 12 choosing shunt regulators. The buffer amplifier sinks current from Regulator A and must have a high slew rate to cover 2 V 8 swing at 50 kHz. The AD8541 buffer satisfies this high slew rate NO ACCELERATION NO ACCELERATION ACCELERATION requirement and also has an ultralow, 100 A quiescent current. 0 TIME (Seconds) Figure 2. IEPE Signal Data Using the ADXL1002 Rev. 0 Page 2 of 6 SIGNAL SUPPLY (V) 21929-002 21929-001 21929-003