LIS2DW12 i2C communication issues

[David Pérez]

Posted on January 26, 2018 at 10:45

Hi to all,

We are usin this accel over i2c with this configuration:

* Separate VDD and VDDIO (this one is attached to CS).

* SDA and SCL are mounted with a external pull up resistor of 10K.

* SDO/SA0 is left unconnected (it is supposed to have an internall pull up).

Is there any power up sequence to ensure the i2c mode is properly configured/selected? Any delay between VDD and VDDIO?

Powering up both lines to 3V, the VDDIO is not 3V, its in 1.9V or similar. If we disconnect CS from VDDIO. In CS we get a '0' and in VDDIO 3V. Is this normal? And the internall pull up resistor does not lift the pin to high?

Is there any example of how to connect the accel for i2c communications? any keynote for the power up?

Attached is an image of the mounted sensor were the marking is a dot, a datamatrix and a 'T'.

Thanks in advance for your help.

#lis2dw12 #i2c

[David Pérez]

Posted on January 26, 2018 at 11:06

Here you have a better image:

[Miroslav BATEK]

Posted on January 26, 2018 at 12:51

The behavior of CS pin is not normal

Can you please check that the CS pin is not shorted with GND? It seems to me it is.

You can power up both VDD and VDDIO at the same time.

[David Pérez]

Posted on January 26, 2018 at 13:17

CS pin and GND are not shorted.

When using a 10k resistor to conect CS to VDDIO the captured oscilo image is the attached one.

pink: SDA

blue: CS

green: SCL

________________ Attachments : tek00007.png : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006HxpP&d=%2Fa%2F0X0000000b43%2FKJUqC5f4DBbw653uvg2BuwGrtpv8wR6.lF4JYmmKNIQ&asPdf=false

[Miroslav BATEK]

Posted on January 26, 2018 at 16:33

Can you please share your schematic or check by yourself the schematic, layout, and pinout in datasheet.

The CS pin is input it should not destroy the signal as it is depicted in your picture from scope.

[David Pérez]

Posted on January 29, 2018 at 07:56

Here is the sch part for the accel.

SCL and SDA lines have an external 10k pull up resistor to i2c_pwr.

VDD and VDD_IO are 3V voltages.

If there is anything wrong or there is something to test or take into account let us know. thanks!

[Miroslav BATEK · Accepted solution]

Posted on January 29, 2018 at 10:14

The schematics is OK, but I compered your schematic, the image of your board and pin out in datasheet, I see they are not aligned.

I added the pin description in your picture and I see for example the CS and SDO pins are connect to your interrupt circuit. So most of the pins have wrong connection. 

Can you please double check your sensor footprint and layout of the boards?

[David Pérez]

Posted on January 30, 2018 at 08:52

You are right, the datasheet specifies the pinout seen from the bottom and we didnt realize it.

We have flipped the component and mounted it properly to check that with right connection the sensor works.

Thanks for your help!