ADIS16305SLASHPCBZ datasheet(14/20 Pages) AD

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ADIS16305

Rev. 0 | Page 14 of 20

Power Management

Setting SMPL_PRD ≥ 0x0A also sets the sensor to low power

mode. For systems that require lower power dissipation, in-

system characterization helps users to quantify the associated

performance trade-offs. In addition to sensor performance, this

mode affects SPI data rates (see Table 2). Set SLP_CNT[8] = 1

(DIN = 0xBB01) to start the indefinite sleep mode, which requires

a CS assertion (high to low), reset, or power cycle to wake up.

Use SLP_CNT[7:0] to put the device into sleep mode for a specified

period. For example, SLP_CNT[7:0] = 0x64 (DIN = 0xBA64)

puts the ADIS16305 to sleep for 50 sec.

Table 21. SLP_CNT Bit Descriptions

Bit(s)

Description

[15:9]

Not used

[8]

Indefinite sleep mode; set to 1

[7:0]

Programmable sleep time bits, 0.5 sec/LSB

Sensor Bandwidth

The signal chain for each MEMS sensor has several filter stages,

which shape their frequency response. Figure 16 provides a block

diagram for both gyroscope and accelerometer signal paths.

Table 22 provides additional information for digital filter

configuration.

LPF

404Hz

FROM

GYROSCOPE

SENSOR

757Hz

LPF

FROM

ACCELERATION

SENSOR

330Hz

N = 2m

m = SENS_AVG[2:0]

Figure 16. MEMS Analog and Digital Filters

Digital Filtering

The N blocks in Figure 16 are part of the programmable low-

pass filter, which provides additional noise reduction on the

inertial sensor outputs. This filter contains two cascaded averaging

filters that provide a Bartlett window, FIR filter response (see

Figure 17). For example, set SENS_AVG[2:0] = 100 (DIN = 0xB804)

to set each stage to 16 taps. When used with the default sample

rate of 819.2 SPS, this value reduces the sensor bandwidth to

approximately 16 Hz.

–20

–40

–60

–80

–100

–120

–140

0.001

0.01

0.1

FREQUENCY (Ratio)

N = 2

N = 4

N = 16

N = 64

Figure 17. Bartlett Window, FIR Filter Frequency Response

(Phase Delay = N Samples)

Dynamic Range

The SENS_AVG[10:8] bits provide three dynamic range settings

for this gyroscope. The lower dynamic range settings (±75°/sec and

±150°/sec) limit the minimum filter tap sizes to maintain resolution.

For example, set SENS_AVG[10:8] = 010 (DIN = 0xB902) for

a measurement range of ±150°/sec. Because this setting can

influence the filter settings, program SENS_AVG[10:8] and

then SENS_AVG[2:0] if more filtering is required.

Table 22. SENS_AVG Bit Descriptions

Bit(s)

Description

[15:11]

Not used

[10:8]

Measurement range (sensitivity) selection

100 = ±300°/sec (default condition)

010 = ±150°/sec, filter taps ≥ 4 (Bits[2:0] ≥ 0x02)

001 = ±75°/sec, filter taps ≥ 16 (Bits[2:0] ≥ 0x04)

[7:3]

Not used

[2:0]

Number of taps in each stage, N = 2M;

maximum setting = 6 (110), N = 26 = 64 taps/stage

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