LDC0851: Sensor cap placement

Bumblebee

Part Number: LDC0851

Hi, I don't understand why the datasheet states that I need to place the sensor cap close to the IC. Why do I need to do this?

over 6 years ago

0 Akeem Whitehead over 6 years ago

TI__Mastermind 27950 points

Hi Bumblebee,

How far apart do you need to space the sensor capacitor from the IC?

From the datasheet's section "11.1 Layout Guidelines", close proximity is required to minimize the effects of parasitic capacitance from the traces, and improve noise-immunity from ambient/radiating antenna effects: "The sensor capacitor should be placed close to the IC and keep traces far apart to minimize the effects of parasitic capacitance. For optimum performance, it is recommended to use a C0G/NP0 for the sensor capacitor."

For further clarification, our LDC specialist is out of office, and will be able to follow-up next week.

0 Bumblebee over 6 years ago in reply to Akeem Whitehead

Expert 2575 points

I need about 1-2 meters. So my question is, if I place the cap near the coil is it bad? If yes, why?

0 Bumblebee over 6 years ago in reply to Bumblebee

Expert 2575 points

hi, any update on this? thanks

0 Bala Ravi over 6 years ago in reply to Bumblebee

TI__Expert 6625 points

Hi Bumblebee,
1-2 meters is too far. You can place the cap near coil as long as its equal distance from the sense coil and ref coil (if there is any influence from the cap it will be nullified by the differential measurement). The reason you should avoid large distances for sensor cap is to avoid unwanted parasitic capacitance, this will effect your resonance frequency. Please download our inductive sensing tool calculator: www.ti.com/.../slyc137. In the tool, find LDC0851_calc, it has some useful calculations needed for your application.

Best Regards,
Bala Ravi

0 Bumblebee over 6 years ago in reply to Bala Ravi

Expert 2575 points

If I use about 1meter cable, how do I place the cap near the coil in such a way that it's equal distance from lsense and lref coils?

0 Clancy Soehren over 6 years ago in reply to Bumblebee

TI__Mastermind 23810 points

Do your sense and ref coils need to be so far away from eachother? If so, you could try splitting your capacitor and put half of the capacitance on the sense and ref coils. This won't be a perfect solution, so you would need to do some testing.

0 Bumblebee over 6 years ago in reply to Clancy Soehren

Expert 2575 points

Okay, will do some testing

0 Bumblebee over 6 years ago in reply to Bala Ravi

Expert 2575 points

Are there any current drivers compatible to increase the cable from sensor to the chip?

0 Clancy Soehren over 6 years ago in reply to Bumblebee

TI__Mastermind 23810 points

Unfortunately, I do not think that will be an option.

Sensors

Sensors forum

LDC0851: Sensor cap placement