ADXL001-500BEZ-R7 datasheet(12/16 Pages) AD

12 / 16 page

ADXL001

Rev. A | Page 12 of 16

APPLICATIONS INFORMATION

APPLICATION CIRCUIT

Figure 20 shows the standard application circuit for the ADXL001.

Note that VDD and VDD2 should always be connected together.

The output is shown connected to a 1000 pF output capacitor

for improved EMI performance and can be connected directly

to an ADC input. Use standard best practices for interfacing

with an ADC and do not omit an appropriate antialiasing filter.

DNC

COM

VDD2

TOP VIEW

(Not to Scale)

VDD

XOUT

DNC

ADXL001

CVDD

0.1µF

XOUT

COUT

1nF

DNC = DO NOT CONNECT

Figure 20. Application Circuit

SELF-TEST

The fixed fingers in the forcing cells are normally kept at the

same potential as that of the movable frame. When the digital

self-test input is activated, the ADXL001 changes the voltage on

the fixed fingers in these forcing cells on one side of the moving

plate. This potential creates an attractive electrostatic force, causing

the sensor to move toward those fixed fingers. The entire signal

channel is active; therefore, the sensor displacement causes a

change in XOUT. The ADXL001 self-test function verifies proper

operation of the sensor, interface electronics, and accelerometer

channel electronics.

Do not expose the ST pin to voltages greater than VS + 0.3 V. If

this cannot be guaranteed due to the system design (for instance, if

there are multiple supply voltages), then a low VF clamping

diode between ST and VS is recommended.

ACCELERATION SENSITIVE AXIS

The ADXL001 is an x-axis acceleration and vibration-sensing

device. It produces a positive-going output voltage for vibration

toward its Pin 8 marking.

PIN 8

Figure 21. XOUT Increases with Acceleration in the Positive X-Axis Direction

OPERATING VOLTAGES OTHER THAN 5 V

The ADXL001 is specified at VS = 3.3 V and VS = 5 V. Note that

some performance parameters change as the voltage is varied.

In particular, the XOUT output exhibits ratiometric offset and

sensitivity with supply. The output sensitivity (or scale factor) scales

proportionally to the supply voltage. At VS = 3.3 V, the output

sensitivity is typically 16 mV/g. At VS = 5 V, the output sensitivity

is nominally 24.2 mV/g. XOUT zero-g bias is nominally equal to

VS/2 at all supply voltages.

3.5

3.0

2.5

2.0

1.5

1.0

3.2

3.7

4.2

4.7

5.2

5.7

SUPPLY VOLTAGE (V)

HIGH LIMIT

LOW LIMIT

NOMINAL ZERO-g

Figure 22. Typical Zero-g Bias Levels Across Varying Supply Voltages

Self-test response in gravity is roughly proportional to the cube

of the supply voltage. For example, the self-test response for the

ADXL001-70 at VS = 5 V is approximately 1.4 V. At VS = 3.3 V,

the self-test response for the ADXL001-70 is approximately

400 mV. To calculate the self-test value at any operating voltage

other than 3.3 V or 5 V, the following formula can be applied:

(STΔ @ VX) = (STΔ @ VS) × (VX/VS)3

where:

VX is the desired supply voltage.

VS is 3.3 V or 5 V.

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