ADXRS649BBGZ Analog Devices Inc, ADXRS649BBGZ Datasheet - Page 9

• Manufacturer Part Number: ADXRS649BBGZ
• Description: ?20,000?/sec Yaw Rate Gyroscope
• Manufacturer: Analog Devices Inc

Specifications of ADXRS649BBGZ

• Rohs Compliant: YES
• No. Of Axes: 1
• No. Of Pins: 32
• Supply Voltage Range: 4.75V To 5.25V
• Operating Temperature Range: -40°C To +105°C
• Sensor Case Style: BGA

THEORY OF OPERATION
The ADXRS649 operates on the principle of a resonator gyro.
Figure 18 shows a simplified version of one of four polysilicon
sensing structures. Each sensing structure contains a dither
frame that is electrostatically driven to resonance. This pro-
duces the necessary velocity element to produce a Coriolis force
when experiencing angular rate. The ADXRS649 is designed to
sense a z-axis (yaw) angular rate.
When the sensing structure is exposed to angular rate, the result-
ing Coriolis force couples into an outer sense frame, which
contains movable fingers that are placed between fixed pickoff
fingers. This forms a capacitive pickoff structure that senses
Coriolis motion. The resulting signal is fed to a series of gain
and demodulation stages that produce the electrical rate signal
output. The quad sensor design rejects linear and angular
acceleration, including external g-forces and vibration. This is
achieved by mechanically coupling the four sensing structures
such that external g-forces appear as common-mode signals
that can be removed by the fully differential architecture
implemented in the ADXRS649.
The electrostatic resonator requires 13 V to 15 V for operation.
Because only 5 V are typically available in most applications,
a charge pump is included on chip. If an external 13 V to 15 V
supply is available, the two capacitors on CP1 to CP4 can be
omitted, and this supply can be connected to CP5 (Pin D6,
Z
X
Figure 18. Simplified Gyro Sensing Structure—One Corner
Y
Rev. A | Page 9 of 12
Pin D7). CP5 should not be grounded when power is applied
to the ADXRS649. No damage occurs, but under certain condi-
tions, the charge pump may fail to start up after the ground is
removed without first removing power from the ADXRS649.
SETTING THE BANDWIDTH
External Capacitor C
chip R
of the ADXRS649 rate response. The −3 dB frequency set by
R
f
during manufacturing to be 180 kΩ ± 1%. Any external resistor
applied between the RATEOUT pin (B1, A2) and the SUMJ pin
(C1, C2) results in
In general, an additional filter (in either hardware or software)
is added to attenuate high frequency noise arising from demodu-
lation spikes at the 18 kHz resonant frequency of the gyro. An
RC output filter consisting of a 3.3 kΩ series resistor and 22 nF
shunt capacitor (2.2 kHz pole) is recommended.
OUT
OUT
can be well controlled because R
f
R
and C
OUT
OUT
OUT
= 1/(2 × π × R
resistor to create a low-pass filter to limit the bandwidth
= (180 kΩ × R
OUT
is
OUT
OUT
EXT
is used in combination with the on-
× C
)/(180 kΩ + R
OUT
)
OUT
has been trimmed
EXT
)
ADXRS649