LDC1000 for automotive use

Thank you Thomas.

The LDC1000 datasheet says that the inductor can be laid out on the PCB.

Does this suggest that the LC tank components should be kept close to the oscillator to minimize parasitics?

In other words, the LC tank should not be used at a remote location separated by wiring harnesses,

interconnects, etc.

Thanks,

Rudy

Placing the sensor (which is the parallel combination of the inductor and capacitor) remotely presents a few considerations. With remote sensors, you may need to put ~10pf to ground near the INA/INB pins. Also, using twisted pair for the INA/INB is recommended. Finally, the farther the distance, the slower the maximum sensor frequency.

How far away are you considering placing the sensor?

Regards,

ChrisO

I am evaluating the feasibility of treating the LC tank as a remote sensor and placing the LDC1000 on the ECU circuit board. The connection would be through a wiring harness up to several feet away. I don't know the internal circuit details of the LDC1000, but I see all kinds of issues with this setup. First, the additional parasitic components of the wiring harness would affect the accuracy; second, the noisy environment (EM) will have an effect; third, the susceptibility of the INA/INB inputs to voltage transients, ESD, shorts to ground/power rails (it's 6V max in the absolute ratings). So, basically, I need to confirm that the INA/INB must not be exposed and may not be protected and rule out this solution.

Thanks,

Rudy

The ABS max specifiactions must be followed, otherwise the device may be damaged. 

Why does the sensor need to be placed so far away from the LDC? There are many options in coil design and positioning which may address the concerns that you have.   

Regards,

ChrisO

Chris,

Generally, this problem would apply to any system in which the sensor(s) and the host microcontroller cannot be in the same location. For example, an ECU monitoring multiple actuators. The sensing element is the LC circuit which would be physically embedded in the measured device. Placing the LDC1000 would be tricky.

If the LDC1000 is placed with the LC circuit and away from the host, then the communication lines will be exposed to harsh environment - all kinds of issues there, bandwidth, emissions, max ratings, etc. If the LDC is placed with the host, away from the sensor, then there are similar limitations.

I think, the resonant circuit, the LDC1000 and the host controller must all be integrated into one standalone assembly and that's the only way to meet the absolute max numbers. One sensor - one controller. Do you agree?

Thank you,

Rudy 

Hi Rudy,

While it is best from an electrical standpoint to have the sensor, LDC1000, and microcontroller all close, you do have options with the LDC1000. For example, you can place the resonant circuit (sensor) and the LDC1000 closer together, and then send the SPI signals a few feet to a remote microcontroller; as conditioning and protecting digital signals is ofen easier than conditioing the analog sensor signal. If you application does require it, you can use the LDC1000 with a remote sensor.  

While there may be some configurations where it is not feasible, in general you can easily support multiple LDC1000 devices with a single microcontroller.