Strange energy leak nRF51288 with ADXL362

RE: Strange energy leak nRF51288 with ADXL362

Stian Røed Hafskjold — Wed, 22 Mar 2017 12:52:36 GMT

Sorry for the late response on this. If you have a floating input you should disable the SPI by writing 0 to the ENABLE register when not active, otherwise you can get some current leaks. The driver does not take care of this so maybe a better solution is to use a pull resistor as you say. You can use an external pull with a higher value (like 1M) if the internal 13k gives you too high current consumption. But to answer your question: GPIOs are not protected against floating levels if configured as input and SPI is enabled and configured to use the input pin.

RE: Strange energy leak nRF51288 with ADXL362

puz_md — Tue, 15 Nov 2016 11:32:09 GMT

Hi Stian,

both nRF and ADXK362 operate on a CR2032 lithium battery. We are using nrf_drv_spi from SDK v11.0.0. Unfortunatelly I cannot post a HEX file. But I can tell you that the problem only seems to occur with the manufactured boards and not when uswing a nRF51-SDK with a small ADXL362 evaluation board, so I can understand when you cannot reproduce the issue.

At the moment, we are going fine with configuring a pull-up on MISO, but I would like to understand how this can happen (to prevent issues in future designs). Can you confirm that the nRF I/O pins (in Input configuration) are protected against floating levels by hardware design to prevent current leaks? If this is the case, my assumption is that the ADXL362 has some internal issues. (Actually, I also had issues with this device in the past when I couldn't read correct data from the registers, it appeared like the ADXL362 did not evaluate CLK reliably back then (e.g. randomly shift two bits on one clean CLK edge)).

RE: Strange energy leak nRF51288 with ADXL362

Stian Røed Hafskjold — Thu, 10 Nov 2016 15:18:49 GMT

Hi,

I've been trying to reproduce this without any luck. As long as the MISO voltage is not higher than the nRF_VDD it shouldn't flow any current. What is the VDD voltage of the ADXL362 and nRF51? Are you using the SPI SDK library in SDK 11? Are you able to post a hex file so I can try to measure it, or post some lines of code that would reproduce the issue? If you don't want to share any hex-files or code here on Devzone you can open up a confidential support case here: www.nordicsemi.com/.../Contact-Support-Team. Please remember to link to this post.