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Best Engineering practices when using ADXL accelerometers

Introduction

This document intention is to provide some tips and basic considerations when using ADI ADXL accelerometers. We thank you for choosing ADI and want to let you know that our main focus is to offer High Performance Inertial Sensors for the most demanding applications.

The first and most important advise we would like to offer when using our ADXL portfolio is to carefully read the product datasheet, this can save you precious time.

Power supply considerations

It is important to respect the power supply limits and considerations described in the datasheet.

As a general rule, it is highly recommended to always be started up the accelerometer from ground level (0 V).

Some products, e.g. ADXL313, specifies that VS and VDDIO can be applied in any sequence without damaging the part, whereas the the ADXL355 specifies that, VS cannot be powered before VDDIO.

Power supply decoupling specifications

Generally it is recommend to use a 0.1uF ceramic capacitor and a 1-to-10uF tantalum capacitor between VS/VDDIO. Following this recommendation is very important to meet the datasheet specifications, for example in terms of noise level.

Power Cycling

It is common in ULP applications to power cycle the accelerometer to reduce power consumption. When using this technique, please remember that it is highly recommend to always start up the accelerometer from ground level (0 V) to ensure proper operation. If this is not possible, care must be taken regarding the following specifications:

  • VS supply start-up threshold: During start-up or power cycling, the VS and VDDIO supplies must always be started up from below 200 mV. When the device is in operation, any time power is removed or falls below the accelerometer power supply lower range voltage, VS and VDDIO supplies must be discharged below 200 mV. This specification is mandatory.
  • Hold time: VS and VDDIO supplies must be held below 200 mV for at least 100 ms before re-powering the part.
  • Rise time: For the worst case scenario, 200mV Vs starts up and 100ms hold time, VS and VDDIO supplies rise time must be linear and within 45 μs to reach the supply lower range voltage. For example, for the ADXL372, the power supply lower range voltage is 1.6V, thus the voltage supply should raise from 0V to 1.6V within 45μs.

Hold time and rise time specifications can vary. For example, if hold time is much longer than 100ms, the rise time criteria might be relaxed. The user should carefully select the start-up specifications that suits their application.

Fully discharging the power supply to ground level allows a much more relaxed rise time (≤ 500µs, from 0V to the power supply lower range voltage) and hold time as low as 10µs.

To enable supply discharge, it is recommended to power the device from a microcontroller general-purpose input/output (GPIO), connect a shutdown discharge switch to the supply, or use a voltage regulator with a shutdown discharge feature.

resources/technical-guides/best_engineering_practices_when_using_adxl_accelerometers.1613486217.txt.gz · Last modified: 16 Feb 2021 15:36 by Pablo del Corro