ADIS16251 Analog Devices, ADIS16251 Datasheet - Page 14

• Manufacturer Part Number: ADIS16251
• Description: Programmable Low Power Gyroscope
• Manufacturer: Analog Devices

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DataSheet
ADIS16251
CALIBRATION
The ADIS16251 is factory-calibrated for sensitivity and bias. It
also provides several user calibration functions for simplifying
field-level corrections. The calibration factors are stored in
nonvolatile memory and are applied using the following linear
calibration equation:
There are three options for system-level calibrations of the bias
in the ADIS16251: auto null, factory calibration restore, and
manual calibration updates. The auto null and factory reset
options are described in the Global Commands section.
Optional field-level calibrations use the above equation and
require two steps:
(1) characterize the behavior of the ADIS16251 at predefined
critical operating conditions, and (2) use this characterization
data to calculate and load the appropriate adjustment factors
into the GYRO_OFF (“b”). The GYRO_SCALE (“m”) register
can also be adjusted to implement corrections in the sensitivity
scale factor through the system calibration process.
The GYRO_OFF provides a calibration range of ±37.5°/sec, and
its contents are nonvolatile. The GYRO_SCALE register
provides a calibration range of 0 to 1.9995, and its contents are
nonvolatile as well.
Table 9. GYRO_OFF Register Definition
Address
0x11,
0x10
1
Table 10. GYRO_OFF Bit Designations
Bit
15:12
11:0
Table 11. GYRO_SCALE Register Definition
Address
0x13, 0x12
1
Table 12. GYRO_SCALE Bit Designations
Bit
15:12
11:0
Refer to AN-879 for a detailed description of calibrating the
ADIS16251, and other MEMS gyroscopes.
Scale is the weight of each LSB.
Scale is the weight of each LSB.
4
Where
m
y
y
U
=
=
=
.com
mx
Calibrated
Sensitivit
Description
Not used
Data bits
Description
Not used
Data bits
:
+
Scale
0.018315°/sec
b
Scale
0.0488%
y
1
output
scale
1
factor
data
2
Equates to a scale factor of one..
Default
0x0000
Default
0x0800
x
b
=
=
Pre
Offset
-
2
calibratio
Format
Twos
complement
scale
Format
Binary
factor
n
data
Access
R/W
Access
R/W
Rev. PrA | Page 14 of 20
GLOBAL COMMANDS
The ADIS16251 provides global commands for common
operations, such as auto null, factory calibration restore, manual
FLASH update, auxiliary DAC latch, and software reset. Each of
these global commands have a unique control bit assigned to
them in the COMMAND register and are initiated by writing a 1 to
its assigned bit.
The auto null function does two different things: it resets the
contents of the ANGL_OUT register to zero and it adjusts the
GYRO_OUT register to zero. This automated adjustment takes
twos steps: (1) read GYRO_OUT and (2) write the opposite of
this value into the GRYO_OFF register. Sensor noise influences
the accuracy of this step. For optimal calibration accuracy, set
the number of filtering taps to its maximum, wait for the
appropriate number of samples to process through the filter,
and then exercise this option.
The “factory calibration restore” command sets the contents of
GYRO_OFF to 0x0000 and GYRO_SCALE to 0x0800, erasing
any field-level calibration contents. The manual FLASH update
writes the contents of each nonvolatile register into FLASH
memory for storage. This process takes approximately 50 ms
and requires the power supply voltage to be within specification
for the duration of the event. It is worth noting that this
operation also automatically follows the auto null and factory
reset commands.
The DAC latch command loads the contents of AUX_DAC into
the DAC latches. Since the AUX_DAC contents must be
updated one byte at a time, this command ensures a stable DAC
output voltage during updates. Finally, the software reset
command sends the ADIS16251’s digital processor into a re-
start sequence, effectively doing the same thing as the RST line.
Table 13. COMMAND Register Definition
Address
0x3F, 0x3E
Table 14. COMMAND Bit Descriptions
Bit
15:8
7
6:4
3
2
1
0
Description
Not used
Software reset command
Not used
Manual FLASH update command
Auxiliary DAC data latch
Factory Calibration Restore command
Auto null command
Default
N/A
Preliminary Technical Data
Format
N/A
Access
Write only