LDC0851: External multiplexer

Hi TTD,

The LDC2114 cannot be used with an external multiplexer.

For the LDC0851, the OUT pin updates right after the ref and sense oscillation cycles are completed so using an external mux will require you to sample the OUT pin at some set interval dependent on the MUX cycling.

Would you be able to provide any information about the end application, there might be a better part in our portfolio to suit your application needs.

Regards,

Varn.

Hi Varn,

I'd like to detect the pencil which color is set.

Color variations are over 30, so multiplex is required to detect the color by LDC0851.

See attached file.

LDC0851.pdf

I you have any idea, could you share it?

Best Regards,

ttd

Hi ttd,

Short answer for your approach is that yes, it is possible but is not a very neat solution. You will have to control both the MUX and EN pin on the LDC0851 and ensure you give enough time for two consecutive conversions ( REF and SENSE) measure the OUT, timing will be critical.

In addition it isn't clear how big the geometries of the sensor are going to be? If the sensors are really small (resonate at a high frequency) and placed close to each other and the MUX basically leaves the inactive channels floating, there is possibility of cross-talk.

Since the targets you are trying to identify will all have a different inductance response, you can address the application using a LDC1101 in LHR mode and just one sensor. This approach requires processing data from the I2C lines.

And it seems like you only have four different targets from the drawing, if so you can always just use the LDC2114 without a mux or use multiple LDC2114s if more than 4 channels. The LDC2114 will allow you to keep your current/simpler approach. The LDC2114 also lets you support much smaller sensor geometries and remote sensors.

Regards,

Varn.