Abstract: The ADXL190 is a low-power, low-cost, and fully functional acceleration measurement system launched by Analog Devices (ADI). It can measure positive and negative accelerations, with a maximum measurement range of ±100g, making it suitable for vibration and shock measurements. This paper details the working principle, calibration, ESD protection device, 0g point offset adjustment method, and applications of the ADXL190. Keywords: sensor; analog signal output; accelerometer; application 1. Overview The ADXL190 accelerometer is a complete acceleration measurement system integrated on a single chip. It consists of a polysilicon surface-mount micromechanical sensing element and signal conditioning circuitry, and can measure positive and negative accelerations. The ADXL190 has the following characteristics: it is a monolithic integrated circuit accelerometer integrating a single-axis acceleration sensor; resolution up to 4010-3g; low power consumption (<2mA); bandwidth of 400Hz; +5V single power supply; and can withstand 2000g of vibration and shock. The main applications of the ADXL190 are vibration and shock measurement; safety inspection of mechanical devices; vehicle recorders; and military applications for protection and safety monitoring. 2. Working Principle The ADXL190 integrates a micromechanical sensor with a polysilicon surface and signal loop circuitry onto a single chip, forming an open-loop acceleration measurement mechanism. It can measure both positive and negative accelerations, with a maximum measurement range of ±100g, making it suitable for vibration and shock measurements. Figure 1 shows the functional block diagram of the ADXL190. The typical noise level of the ADXL190 is 4 × 10⁻³ g/(Hz)¹/², and the detected acceleration signal can be below 40 × 10⁻³ g. It can measure both dynamic accelerations (such as typical vibrations and shocks) and static accelerations (such as gravitational acceleration and inertia). The ADXL190 contains a two-stage Bessel switched-capacitor filter. Bessel filters, sometimes called linear phase filters, have a first-order response with minimal overtuning and the flattest group delay. At the factory, the frequency at -3dB of this filter is preset to 400Hz. The filter has a complete structure and requires no external components. This product has a built-in self-test component, possessing both mechanical and electronic characteristics. When its self-test pin is triggered by a high-level digital signal, an electrostatic force is applied to the crossbeam, equivalent to approximately 20% of the full-scale acceleration input, thus generating a proportional voltage change on the output pin. Only a decoupling capacitor is needed to achieve the self-test function. The circuitry used to drive the sensor and convert capacitance changes into voltage changes is integrated on the same chip, requiring no external components except for a standard power supply decoupling device. For the supply voltage, the sensitivity (S) and acceleration zero-point value are calculated proportionally. When the supply voltage changes, the output following the accelerometer (such as an analog-to-digital converter) also changes accordingly. The output voltage Vout is the result of the combined effect of the accelerometer input (a) and the supply voltage (Vs), and its calculation formula is given. The ADXL190 uses a hermetically sealed 14-pin surface-mount package and operates within a temperature range of -40℃ to 105℃. Figure 2 shows the pinout of the ADXL190. 3. Application Technology 3.1 Pin Functions and Connection Methods Vs (pins 13, 14) are voltage input terminals, directly connected to the positive power supply, with a power supply range of -0.3V to +7.0V. COMMON (pin 7) is the ground terminal, directly connected to the negative power supply. A decoupling capacitor with a capacitance of 0.1μF should be connected between Vs and COM to form a power supply decoupling circuit. Vout (pin 10) is the voltage signal output terminal, i.e., the sensor's output port. SELF-TEST (pin 9) is the self-test terminal. When connected to Vs, electrostatic force is applied to the crossbeam, equivalent to approximately 20% of the full-scale acceleration input, thus generating a proportional voltage change on the output pin. TESTPOINT (pin 5) is the detection terminal and is not connected to any device. ZEROgADJUST (pin 8) is the calibration terminal for acceleration 0g. NC (pins 1, 2, 3, 4, 6, 11, 12) are empty pins and should not be connected. 3.2 ADXL190 Calibration Figure 3 shows the ADXL190's response to Earth's gravitational field, where the voltage output from pin 10 is the rated value. The ADXL190 should be calibrated before use. The ADXL190's special design allows users to perform calibration conveniently and promptly. Calibration coefficients can be stored in EEPROM or dynamic memory. 3.3 0g Point Offset Adjustment Method In some applications, users may have asymmetrical inputs or need to adjust the 0g standard output to obtain the maximum dynamic range. 0g standard adjustment is achieved by applying a voltage to the device's 0g adjustment pin, as shown in Figure 4. As shown in Figure 4, the two resistors inside the ADXL190, 5kΩ and 25kΩ, form a voltage divider with a scaling factor of 6, reducing the voltage difference between the ADXL190's 0g point adjustment pin and Vs/2. A gain of 3x is obtained at the output, while a gain of 0.5x is obtained at the 0g point adjustment pin. It should be noted that the resistor division ratio is consistent for all devices. However, its absolute value has a tolerance of ±30%. The 0g point adjustment voltage can be set in several ways. Figure 4 uses a potentiometer, but it can also be set using a pulse-width modulation signal or a simple tri-state output. The simplest method is to connect a resistor between the 0g point adjustment pin and Vs (or ground), resulting in an output offset of where R is in kΩ, connected to Vs. Alternatively, it can be where R is in kΩ, connected to ground. A second method for 0g point adjustment is to connect two resistors to the microprocessor's input/output pins, as shown in Figure 5. In this figure, since both I/Os can be set to Vs, ground, or tri-state, there are seven possible scenarios (note: setting one I/O to Vs and the other to ground is not possible), as shown in Table 1. Using this system, the ADXL190 can maintain balance and output 2.5V ± 35mV at the 0g terminal. The third method for 0g-point adjustment involves applying a voltage to the 0g-point adjustment pin. Due to the voltage division effect of the internal 5kΩ and 25kΩ resistors, the voltage difference between the 0g-point adjustment pin 8 and Vs/2 is reduced by a factor of 6. Multiplying this by the output gain of 3 yields a total gain of 0.5. The bias voltage can then be calculated using the following equation: Alternatively, the 0g-point adjustment voltage can also be set by outputting a pulse-width modulation signal from the microprocessor. However, it is important to note that the output impedance of this voltage source should be less than 5kΩ and the signal noise should be low. Any noise at the 0g-point adjustment pin can lead to output errors. If an asymmetrical acceleration range (e.g., +75g to -125g) is required, a resistor should be connected between the 0g-point adjustment terminal and ground or VS, as described above. For example, to obtain an acceleration range of +75g to -125g with an offset of -25g, the required offset voltage should be Voffset=450mV. Substituting this into equation (6), we get R=53.3kΩ, meaning a resistor with a resistance of 53.3kΩ should be connected between the 0g adjustment terminal and ground. Generally, for asymmetrical acceleration ranges, the midpoint of the acceleration range should be shifted ±80g. 3.4 Protection against electrostatic discharge (ESD) Static charges up to 4000V can easily accumulate on the human body and testing equipment, potentially discharging unnoticed. Therefore, to prevent high-energy ESD from damaging device functionality or causing permanent performance degradation, proper ESD protection measures must be taken. The ADXL190 is equipped with an ESD protection circuit. The ADXL190's maximum rated parameters are: 2000g, 0.5ms shock without power supply; 1000g, 0.5ms shock with power supply; operating voltage range: -0.3V to +7.0V; unlimited short-circuit time to ground for any pin; operating temperature range: -55℃ to +125℃; storage temperature range: -65℃ to +150℃. It is important to emphasize that the above maximum ratings may cause permanent damage to the accelerometer. Exceeding these absolute maximum ratings for a certain period will affect the device's reliability. If the device is dropped onto a hard surface, it will generate vibrations exceeding 2000g, surpassing its maximum rating; therefore, extreme caution must be exercised during handling.