CN-0274

Circuit Note

Rev. A | Page 4 of 6

Interrupts

Several of the built-in functions of the ADXL362 can trigger

interrupts to alert the host processor of certain status conditions.

Interrupts may be mapped to either (or both) of two designated

output pins, INT1 and INT2, by setting the appropriate bits in

the INTMAP1 and INTMAP2 registers. All functions can be

used simultaneously. If multiple interrupts are mapped to one

pin, the OR combination of the interrupts determines the status

of the pin.

If no functions are mapped to an interrupt pin, that pin is

automatically configured to a high impedance (high-Z) state.

The pins are placed in this state upon a reset as well.

When a certain status condition is detected, the pin that condition

is mapped to is activated. The configuration of the pin is active

high by default, so that when it is activated, the pin goes high.

However, this configuration can be switched to active low by

setting the INT_LOW pin in the appropriate INTMAP register.

The INT pins may be connected to the interrupt input of a host

processor and interrupts responded to with an interrupt routine.

Because multiple functions can be mapped to the same pin, the

STATUS register can be used to determine which condition

caused the interrupt to trigger.

The CN0274 evaluation software configures the ADXL362 such

that when activity is detected, the INT1 pin is high, and when

inactivity is detected, the INT1 pin is low.

Test Results

All testing was performed using the EVAL-CN0274-SDPZ and

the EVAL-SDP-CS1Z. Functionality of the part is demonstrated

by setting the activity threshold at 0.5 g, the inactivity threshold

at 0.75 g, and the number of inactivity samples at 20. When

looking for activity, only one acceleration sample on any axis is

required to cross the threshold.

Starting with the circuit oriented so that the battery pack is flat

against the table, the printed circuit board (PCB) can be slowly

rotated 90° in any direction causing the acceleration to cross the

threshold as it approaches perpendicular to the initial orientation.

Figure 2 shows a screen shot of the CN0274 evaluation software

showing the ADXL362 first asleep, looking for activity. Then,

when Sample 11 crosses the threshold, the ADXL362 enters the

awake state and begins looking for inactivity. The thresholds

adjust to show the device is now looking for inactivity.

Figure 2. Screen Shot of Evaluation Software Output

For better visibility, the X-axis and Z-axis plots are disabled

using the radio buttons above the chart.

The output of the ADP195, or the interrupt pin itself, was

measured using a digital multimeter. When the ADXL362 is awake,

the interrupt goes high and drives the EN pin of the ADP195

high, which in turn drives the gate of the MOSFET low, causing the

switch to close, connecting any downstream circuitry to the power

supply. Conversely, when the ADXL362 is asleep, the interrupt

drives the EN pin of the ADP195 low, which in turn drives the

gate of the MOSFET high, causing the switch to open.

PCB Layout Considerations

In any circuit where accuracy is crucial, it is important to

consider the power supply and ground return layout on the

board. The PCB should isolate the digital and analog sections as

much as possible. The PCB for this system was constructed in a

4-layer stack up with large area ground plane layers and power

plane polygons. See the MT-031 Tutorial for more discussion on

layout and grounding, and the MT-101 Tutorial for information

on decoupling techniques.

Decouple the power supply to the ADXL362 with 1 µF and

0.1 µF capacitors to properly suppress noise and reduce ripple.

Place the capacitors as close to the device as possible. Ceramic

capacitors are advised for all high frequency decoupling.

Power supply lines should have as large a trace width as possible

to provide low impedance paths and reduce glitch effects on the

supply line. Shield clocks and other fast switching digital signals

from other parts of the board by digital ground. A photo of the

PCB is shown in Figure 3.

A complete design support package for this circuit note can be

found at www.analog.com/CN0274-DesignSupport.