ADXL355 View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADXL355

Low Noise, Low Drift, Low Power, 3-Axis MEMS Accelerometers

Analog Devices 

ADXL354/ADXL355

THEORY OF OPERATION

The ADXL354 is a complete 3-axis, ultralow noise and ultrastable

offset MEMS accelerometer with outputs ratiometric to the analog

1.8 V supply, V1P8ANA. The ADXL355 adds three high resolution

ADCs that use the analog 1.8 V supply as a reference to provide

digital outputs insensitive to the supply voltage. The ADXL354B

is pin selectable for ±2 g or ±4 g full scale, the ADXL354C is pin

selectable for ±2 g or ±8 g full scale, and the ADXL355 is

programmable for ±2.048 g, ±4.096 g, and ±8.192 g full scale.

The ADXL355 offers both SPI and I2C communications ports.

The micromachined, sensing elements are fully differential,

comprising the lateral x-axis and y-axis sensors and the vertical,

teeter totter z-axis sensors. The x-axis and y-axis sensors and

the z-axis sensors go through separate signal paths that minimize

offset drift and noise. The signal path is fully differential, except

for a differential to single-ended conversion at the analog

outputs of the ADXL354.

The analog accelerometer outputs of the ADXL354 are ratiometric

to V1P8ANA; therefore, carefully digitize them correctly. The

temperature sensor output is not ratiometric. The XOUT, YOUT,

and ZOUT analog outputs are filtered internally with an anti-

aliasing filter. These analog outputs also have an internal 32 kΩ

series resistor that can be used with an external capacitor to set

the bandwidth of the output.

The ADXL355 includes antialias filters before and after the high

resolution Σ-Δ ADC. User-selectable output data rates and filter

corners are provided. The temperature sensor is digitized with a

12-bit successive approximation register (SAR) ADC.

Data Sheet

ANALOG OUTPUT

Figure 57 shows the ADXL354 application circuit. The analog

outputs (XOUT, YOUT, and ZOUT) are ratiometric to the 1.8 V

analog voltage from the V1P8ANA pin. V1P8ANA can be powered

with an on-chip LDO that is powered from VSUPPLY. V1P8ANA can

also be supplied externally by forcing VSUPPLY to VSS, which

disables the LDO. Due to the ratiometric response, the analog

output requires referencing to the V1P8ANA supply when

digitizing to achieve the inherent noise and offset performance

of the ADXL354. The 0 g bias output is nominally equal to

V1P8ANA/2. The recommended option is to use the ADXL354

with a ratiometric ADC (for example, the Analog Devices, Inc.,

AD7682) with V1P8ANA providing the voltage reference. This

configuration results in self cancellation of errors due to minor

supply variations.

The ADXL354 outputs two forms of filtering: internal anti-

aliasing filtering with a cutoff frequency of approximately 1.5 kHz,

and external filtering. The external filter uses a fixed, on-chip,

32 kΩ resistance in series with each output in conjunction with

the external capacitors to implement the low-pass filter antialiasing

and noise reduction prior to the external ADC. The antialias

filter cutoff frequency must be significantly higher than the

desired signal bandwidth. If the antialias filter corner is too low,

ratiometricity can be degraded where the signal attenuation is

different than the reference attenuation.

2.25V TO 3.6V

VDDIO (±4g, ±8g)

GND ( ± 2g)

RANGE 1

ST1 2

ST2 3

TEMP 4

ADXL354

11 VSUPPLY

10 V1P8ANA

9 VSS

8 V1P8DIG

0.1µF

1µF

0.1µF

ADC VREF

1µF

VDDIO (MEASUREMENT)

GND (STANDBY)

2.25V TO 3.6V

1µF

1µF

0.1µF

0.1µF

Figure 57. ADXL354 Application Circuit

Rev. 0 | Page 20 of 42

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