LIS25BA PCB + MKI109V3 Motherboard evaluation - WHO_AM_I register issues

[RRMorris]

I am having trouble evaluating a custom PCB with a LIS25BA accelerometer fitted.

The circuit is exactly the same as ST evaluation board for the same part (STEVAL-MKI211V1 + MKIGIBV3).

When connecting to the motherboard using the ST evaluation board, UNICO is able to connect to the device and all the data and registers are there as they should be (i.e who_am_i = 20h).

When using my own PCB connected to the same pins as the evaluation board the connection fails:

"ERROR: The adapter board has not been recognized.

The WHO_AM_I register value does not match the device selected"

Am I missing a software configuration step over I2C? Is the evaluation board configured to anything other than factory default?

Have I translated the interconnections incorrectly?

I would be grateful for some support on this matter.

Thank you.

Regards,

Robin

[Eleon BORLINI]

Hi Robin @RRMorris​ ,

there is a slight difference between your schematic and the adapter schematic, as I can see from the picture you shared.

In your board, the Vdd / VddIO comes from a custom voltage supplier, while the adapter is directly powered by the ProfiMEMS board (STEVAL-MKI109V3).

If I remember correctly, the Profi board firmware (whose source code is unfortunately not open-source) needs to recognize the adapter from the Vdd line, for example performing a current consumption check on the Vdd to detect the existence of a daughterboard.

I also see that you changed the 1uF capacitor to a 10uF one, but it should not change the circuit behavior.

-Eleon

[RRMorris]

Hi Eleon,

Thank you for replying.

The VDDIO equivalent on my board comes from the same pin as the development board, I have just called it something different in the schematic (1V8).

I have changed the capacitor to 1uF and the board still is not detected.

Surely the current consumption check is not precise enough to detect minute differences in current consumption between boards when there are no component differences?

There must be some other reason. Is the Profiboard checking anything else?

Do you know if there is any additional I2C configuration required before it can be used with the profiboard?

Thanks again.

Kind regards,

Robin

[Eleon BORLINI]

Hi Robin,

Profi should not check anything else...

The current check is very good on the Profi, but it should not be the issue, in this case (your STEVAL-MKIGIBV3 has no resisters on the bottom layer, right?)

Are you connecting all the pins of your custom adapter to the Profi? And did you do any modification to the Profi board?

And did you soldered correctly the LIS25BA on your custom adapter (in the right orientation, I mean).

-Eleon

[RRMorris]

Hi Eleon,

Thanks again for the reply.

I can confirm the interface board (MKIGIBV3) for the evaluation does not have resistors fitted.

I haven't modified the Profiboard.

See attached screenshot of the PCB footprint (Top view) for the LIS25BA in my design, you can see here that pin 1 (i2c_SCL) is top left here.Connected to the profiboard I have the following pinout:

(MyPCB) I2C_GND ->CONNECTED TO -> Profiboard GND (pin 13)

(MyPCB) 1V8 ->CONNECTED TO-> Profiboard VDDIO_DUT (Pin 2)

(MyPCB) TDM_WCLK ->CONNECTED TO-> Profiboard CS_x (Pin 3)

(MyPCB) TDM_BCLK ->CONNECTED TO-> Profiboard SC_x (Pin 4)

(MyPCB) TDM_MCLK ->CONNECTED TO-> Profiboard SD_x (Pin 5)

(MyPCB) TDM_SDOUT ->CONNECTED TO-> Profiboard SDO_x (Pin 6)

(MyPCB) I2C_SDA ->CONNECTED TO-> Profiboard SDA (Pin 21)

(MyPCB) I2C_SCL ->CONNECTED TO-> Profiboard SCL (Pin 20)

On my PCB I2c_SA0 is pulled to ground through a 0R link which makes the i2c address the same as the ST EVAL MKI211V1.

Any other ideas what my issue could be?

Thanks again.

Kind regards,

Robin