ADXL362 - No response on the MISO line


#1

I am working with the ADXL362 but can not get the sensor to respond. I am powering the sensor using 2V , even using resistors of 22ohms along the connections as suggested in previous discussions on this topic.
The CS, MOSI and clk seem fine but for reasons unknown I cannot figure out on why the sensor does not respond.

Any kind of information or suggestions would be of great help.

Thanks!


#2

So, VDDIO should be 3.3v even if VS is 2.0 - though really, why are you running from 2.0v? (the power this thing takes is minimal, easier just to run it from the same rail).


#3

I am working with a custom made chip that handles the power supply for the sensor. Do you suggest change the voltage to 3.3V?

I did go through the data sheet, so I guess you are suggesting 3.3 V to reduce the noise to the most. Do you also suggest changing the resistors that were used?


#4

Mainly, this part is designed to work in super low power situations from a single coin cell - which start at ~3v and are discharged at about ~2.5v, hence the chip can work down to 2.0. In a wifi application, you’re likely to be using an LDO to generate the 2.0v from 3.3v anyway, so the current usage is identical if you run it from 3.3v vs 2.0v - the extra power is just burnt in the LDO vs the sensor.

The critical thing here is whether VDDIO is powered from 3.3v. If VDDIO is 2.0v, then the high level output on the MISO line will be 2.0v. Vih(min) - the voltage at which a logic 1 is reliably registered - for 3.3v devices is 0.7x3.3 = 2.31v. Hence, your MISO may be working, but the imp can’t see logic 1 as the voltage is too low.

Series resistors in the path are usually to reduce noise/overshoot (source termination). They’re important at high speeds and for production designs, but won’t affect the interfacing much here.

Summary: I think your problem may be VDDIO being 2.0v.


#5

Hi Hugo,

I am using the breakout board for the ADXL362, so the VS and VDDIO are at 2V now. I did change the voltage to 3.3V but my MISO line still does not look as expected.

Capture


#7

So can you clarify what “does not look as expected” means? Can you post your code?