ADXL366 datasheet(63/71 Pages) AD

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Data Sheet

ADXL366

APPLICATIONS INFORMATION

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Rev. 0 | 63 of 71

POWER SUPPLY REQUIREMENTS

The ADXL366 operates using supply voltage rails ranging from

1.1V to 3.6V. The operating voltage (VS) range specified in Table 1

ranges from 1.1V to 3.6V to account for inaccuracies and transients

of up to ±10% on the supply voltage. Although the run time supply

current is much lower, during power-up or software reset, the

supply current must be greater than 250μA, which ensures that

the internal fuses are loaded correctly. When power cycling the

ADXL366, it is highly recommended to fully discharge the device to

ground level (VS = 0V) on each power cycle. If this is not possible,

care must be taken regarding the following specifications:

►

Supply reset threshold (VRESET)

►

Hold time

►

Rise time

Supply Reset Threshold

During start-up or power cycling of the ADXL366, VS must be

increased from its previous value, which was less than VRESET.

When the device is in operation, any time power is removed from

the ADXL366 or falls to less than 1.1V, VS must be discharged to a

value less than VRESET.

Hold Time

To ensure a successful power-on reset, VS must be held at a value

that is less than VRESET for at least 300ms before reapplying the

supply to the device (see Figure 63).

Rise Time

The supply voltage rise time is defined as the time from 0V to 90%

of VS, which is true regardless of what VS is used (see the Power

Supply Requirements section).

Figure 63. Power Supply Reset and Start-Up Requirements

To enable supply discharge, it is recommended to power the device

from a microcontroller GPIO, connect a shutdown discharge switch

to the supply, or use a voltage regulator with a shutdown discharge

feature.

Following power-on reset, the output requires 100ms to settle after

entering measurement mode.

Power Supply Decoupling

Figure 64 shows the recommended bypass capacitors for use with

the ADXL366.

Figure 64. Recommended Bypass Capacitors

A 0.1µF ceramic capacitor (named CS) at the VS pin and a 0.1µF

ceramic capacitor (named CIO) at the VDDIO pin are placed as close

as possible to the ADXL366. Supply pins are recommended to

adequately decouple the accelerometer from noise on the power

supply. It is also recommended that VS and VDDIO be separate

supplies to minimize digital clocking noise on VS. If this is not

possible, additional filtering of the supplies may be necessary.

When using separate supplies, power VDDIO and VS simultaneously

to avoid a possible current surge (up to 1mA) on the internal power

on reset circuitry.

If additional decoupling is necessary, place a resistor or ferrite

bead, no larger than 100Ω, in series with VS. Additionally, increas-

ing the bypass capacitance on VS to a 1µF tantalum capacitor in

parallel with a 0.1µF ceramic capacitor may also improve noise.

Note that increasing the resistor and capacitor values increases the

RC time constant, which affects the reset time of the device and

means the user requires a longer reset time. Note that the turn-on

time may also be slower.

Ensure that the connection from the ADXL366 ground to the pow-

er supply ground has low impedance because noise transmitted

through ground has an effect similar to noise transmitted through

VS.

For a single-supply condition, the decoupling schematics, as shown

in Figure 65, can be considered if additional decoupling is necessa-

ry. The resistance between VS and VDDIO must be no greater than

10Ω.

Figure 65. Recommended Decoupling Schematics for Single Supply

ADXL366 Datasheet(PDF) 63 Page - Analog Devices

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