ADXL213AE Analog Devices Inc, ADXL213AE Datasheet - Page 8

• Manufacturer Part Number: ADXL213AE
• Description: IC ACCELER DUAL AXIS DGTL 8-CLCC
• Manufacturer: Analog Devices Inc

Specifications of ADXL213AE

• Acceleration Range: ±1.2g
• Axis: X, Y
• Sensitivity: 30°/g
• Voltage - Supply: 3 V ~ 6 V
• Output Type: Digital
• Bandwidth: 1Hz ~ 500Hz Selectable
• Mounting Type: Surface Mount
• Package / Case: 8-CLCC
• No. Of Axes: 2
• Sensor Case Style: LCC
• No. Of Pins: 8
• Supply Voltage Range: 3V To 6V
• Operating Temperature Range: -40°C To +85°C
• Msl: MSL 1 - Unlimited
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: ADXL213EB - BOARD EVALUATION FOR ADXL213
• Interface: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

ADXL213
THEORY OF OPERATION
The ADXL213 is a complete dual axis acceleration measure-
ment system on a single monolithic IC. It contains a polysilicon
surface-micromachined sensor and signal conditioning
circuitry to implement an open-loop acceleration measurement
architecture. The output signals are duty cycle modulated
digital signals proportional to acceleration. The ADXL213 is
capable of measuring both positive and negative accelerations to
±1.2 g. The accelerometer can measure static acceleration forces
such as gravity, allowing the ADXL213 to be used as a tilt
sensor.
The sensor is a surface-micromachined polysilicon structure
built on top of the silicon wafer. Polysilicon springs suspend the
structure over the surface of the wafer and provide a resistance
against acceleration forces. Deflection of the structure is mea-
sured using a differential capacitor that consists of independent
fixed plates and plates attached to the moving mass. The fixed
plates are driven by 180° out-of-phase square waves. Accelera-
tion deflects the beam and unbalances the differential capacitor,
resulting in an output square wave whose amplitude is propor-
tional to acceleration. Phase sensitive demodulation techniques
are then used to rectify the signal and determine the direction
of the acceleration.
The output of the demodulator is amplified and brought off-
chip through a 32 kΩ resistor. At this point, the user can set the
signal bandwidth of the device by adding a capacitor. This
filtering improves measurement resolution and helps prevent
aliasing.
X
Y
OUT
OUT
= 50%
= 20%
PIN 8
Figure 21. Output Response vs. Orientation
(Not to Scale)
X
Y
X
Y
TOP VIEW
OUT
OUT
OUT
OUT
Rev. A | Page 8 of 12
PIN 8
PIN 8
= 80%
= 50%
= 20%
= 50%
After being low-pass filtered, the duty cycle modulator converts
the analog signals to duty cycle modulated outputs that can be
read by a counter. A single resistor (R
complete cycle. A 0 g acceleration produces a 50% nominal duty
cycle. The acceleration can be determined by measuring the
length of the positive pulse width (t1) and the period (t2). The
nominal transfer function of the ADXL213 is
Where in the case of the ADXL213
PERFORMANCE
Rather than using additional temperature compensation
circuitry, innovative design techniques have been used to ensure
that high performance is built in. As a result, there is essentially
no quantization error or nonmonotonic behavior, and
temperature hysteresis is very low (typically less than 10 mg
over the –40°C to +85°C temperature range).
Figure 9 shows the zero g output performance of eight parts (X
and Y axis) over a –40°C to +85°C temperature range.
Figure 12 demonstrates the typical sensitivity shift over
temperature for V
V
typically better than ±2% over temperature at V
S
= 5 V, but is still very good over the specified range; it is
PIN 8
X
Y
OUT
OUT
EARTH'S SURFACE
Acceleration = ((t1/t2) – Zero g Bias)/Sensitivity
= 50%
= 80%
X
Y
OUT
OUT
S
Sensitivity = 30%/g nominal
= 50%
= 50%
Zero g Bias = 50% nominal
= 5 V. Sensitivity stability is optimized for
t2 = R
SET
/125 MΩ
SET
) sets the period for a
S
= 3 V.