ADIS16364 Datasheet, PDF (11/16 Pages) Analog Devices – Six Degrees of Freedom Inertial Sensor

Preliminary Technical Data
OUTPUT DATA REGISTERS
Figure 6 provides the positive measurement direction for each
inertial sensor (gyroscope and accelerometers). Table 9 provides
the configuration and scale factor for each output data register
in the ADIS16364. All inertial sensor outputs are 14 bits in
length and are in twos complement format, which means that
0x0000 is equal to 0 LSB, 0x0001 is equal to +1 LSB, and 0x3FFF
is equal to −1 LSB. The following is an example of how to
calculate the sensor measurement from the XGYRO_OUT:
XGYRO_OUT = 0x3B4A
0x000 − 0x33B4A = −0x04B6 = −(4 × 256 + 11 × 16 + 6)
− 0x04B6 = −1206 LSB
Rate = 0.05°/sec × (− 1206) = −60.3°/sec
Therefore, an XGYRO_OUT output of 0x3B4A corresponds to
a clockwise rotation about the z-axis (see Figure 6) of 60.3°/sec
when looking at the top of the package.
Table 9. Output Data Register Formats
Register
Bits Format
SUPPLY_OUT 12 Binary, 5 V = 0x0814
XGYRO_OUT¹ 14 Twos complement
YGYRO_OUT¹ 14 Twos complement
ZGYRO_OUT¹ 14 Twos complement
XACCL_OUT 14 Twos complement
YACCL_OUT 14 Twos complement
ZACCL_OUT 14 Twos complement
XTEMP_OUT² 12 Twos complement
YTEMP_OUT² 12 Twos complement
ZTEMP_OUT² 12 Twos complement
AUX_ADC
12 Binary, 1 V = 0x04D9
Scale
2.42 mV
0.05°/sec
0.05°/sec
0.05°/sec
1 mg
1 mg
1 mg
0.14°C
0.14°C
0.14°C
0.81 mV
1 _{Assumes that the scaling is set to ± 300°/sec. This factor scales with the range.}
2 _{Note that typically, +25°C, these registers read 0x0000.}
Each output data register uses the bit assignments shown in
Figure 13. The ND flag indicates that unread data resides in the
output data registers. This flag clears and returns to 0 during an
output register read sequence. It returns to 1 after the next
internal sample updates the registers with new data. The EA flag
indicates that one of the error flags in the DIAG_STAT register
(see Table 21) is active (true). The remaining 14 bits are for data.
MSB FOR 14-BIT OUTPUT
ND EA
MSB FOR 12-BIT OUTPUT
Figure 13. Output Register Bit Assignments
Auxiliary ADC
The AUX_ADC register provides access to the auxiliary ADC
input channel. The ADC is a 12-bit successive approximation
converter, which has an equivalent input circuit to the one
in Figure 14. The maximum input range is +3.3 V. The ESD
protection diodes can handle 10 mA without causing irreversible
damage. The switch on-resistance (R1) has a typical value of
100 Ω. The sampling capacitor, C2, has a typical value of 16 pF.
ADIS16364
VCC
D
C1
D
R1 ^C2
Figure 14. Equivalent Analog Input Circuit
(Conversion Phase: Switch Open,
Track Phase: Switch Closed)
CALIBRATION
Manual Bias Calibration
The bias offset registers in Table 10 and Table 11 provide a manual
adjustment function for the output of each sensor. For example,
if XGYRO_OFF equals 0x1FF6, the XGYRO_OUT offset shifts
by −10 LSBs, or −0.125°/sec. The DIN command for the upper
byte is DIN = 0x9B1F; for the lower byte, DIN = 0x9AF6.
Table 10. XGYRO_OFF, YGYRO_OFF, ZGYRO_OFF
Bits
Description
[15:13]
Not used.
[12:0]
Data bits. Twos complement, 0.0125°/sec per LSB.
Typical adjustment range = ±50°/sec.
Table 11. XACCL_OFF, YACCL_OFF, ZACCL_OFF
Bits
Description
[15:12]
Not used.
[11:0]
Data bits, twos complement 1 mg/LSB.
Typical adjustment range = ±2 g.
Gyroscope Automatic Bias Null Calibration
Set GLOB_CMD[0] = 1 (DIN = 0xBE01) to execute this function,
which measures XGYRO_OUT and then loads XGYRO_OFF
with the opposite value to provide a quick bias calibration.
Then, all sensor data resets to 0, and the flash memory updates
automatically (50 ms). See Table 12.
Gyroscope Precision Automatic Bias Null Calibration
Set GLOB_CMD[4] = 1 (DIN = 0xBE10) to execute this
function, which takes the sensor offline for 30 sec while it
collects a set of XGYRO_OUT data and calculates a more
accurate bias correction factor. Once calculated, the correction
factor loads into XGYRO_OFF, all sensor data resets to 0, and
the flash memory updates automatically (50 ms). See Table 12.
Restoring Factory Calibration
Set GLOB_CMD[1] = 1 (DIN = 0xBE02) to execute this function,
which resets each user calibration register (see Table 10 and
Table 11) to 0x0000, resets all sensor data to 0, and auto-
matically updates the flash memory (50 ms). See Table 12.
Linear Acceleration Bias Compensation (Gyroscope)
Set MSC_CTRL[7] = 1 (DIN = 0xB486) to enable correction for
low frequency acceleration influences on gyroscope bias. Note
that the DIN sequence also preserves the factory default condi-
tion for the data ready function (see Table 17).
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