ADXL362 Motion Switch Issues

I am using the ADXL362 as a motion switch to turn on the uP in my design. The following sequence works on most of the devices. They are all built the same. 

For the most part the units work and are turned on with motion and turn off with 3 min of inactivity. However, some devices never turn off. I can read and write to the parts the exhibit this behavior. Some devices work for a month or so and then cease to turn off, draining the battery on customer products. Has anyone experienced this issue?

****When INT1 is low, the uP is ON***

*****The INT1 pin is pulled low with a pulldown resistor to ensure default state of uP is on.

2) The uP programs the following to the ADXL362: 

Write to 0x52 to register 0x1F - Reset 

Write 0xF4 to register 0x20 - Set Activity Threshold

Write 0x01 to register 0x21- Set Activity Threshold

Write 0x00 to register 0x22 - Set Activity Time

Write 0x96 to register 0x23 - Set Inactivity Threshold

Write 0x00 to register 0x24 - Set Inactivity Threshold

Write 0x38 to register 0x25- Set Inactivity Timer

Write 0x04 to register 0x26 - Set Inactivity Timer

Write 0x3F to register 0x27 - Configure motion detection in loop mode and enables reference activity and inactivity

Write 0xC0 to register 0x2A - Map awake bit to INT1 and make it active low

Write 0x0E to register 0x2D - Begin measurement in wakeup mode and enable auto sleep

    •  Analog Employees 
    on Feb 15, 2019 5:12 PM over 1 year ago

    Thanks for the question. It looks like the part is latched and draws current. Does power cycling fix the issue? If so, can you check if the power supply always stays above 1.6v all the time? Please note that when the device is in operation, any time power is removed from the ADXL362, or falls below the operating voltage range(e.g. due to power glitch), the supplies must be discharged completely before power is reapplied. 

  • Hi,  thank you for the response.  The part is powered through a 3 volt regulator that is on as soon as a battery is installed.  Upon installation,  the unit turns on and the uP toggles a switch that discharges the ADXL362.  After that , the unit gets  programmed with the code provided.  When the unit shuts down, and then powers up again,  the uP discharges the supplies again before reprogramming.  Should I allow more time for discharge?  I currently discharge it for 20ms before programming. The switch provides a path to ground on all of the supplies when toggled. Thank you again for responding. Is there any other way that could cause a latch? 

    •  Analog Employees 
    on Feb 15, 2019 8:30 PM over 1 year ago in reply to Grs6

    You need to make sure it complete discharges before reprogramming. Let's say Vs< 200ms for at least 20ms.(I know some customer may even delay 200ms). The issue is due to the drop of voltage causing the oscillator to stop. We haven't experienced any else that would case the latch problem.

  • Thank you, I'll try it and see if this helps resolve the issue.