Inductance-to-digital converters: precise position and motion sensing

April 28, 2015 // By Graham Prophet
Texas Instruments claims a technology first for its multichannel inductance-to-digital converters (LDCs). The four new devices in the LDC1614 family expand the LDC portfolio, a data converter category that TI first introduced in 2013. The devices offer two or four matched channels and up to 28-bit resolution in a single integrated circuit.

The combination of precision and multichannel functionality will allow engineers to design high dynamic range position and motion sensing solutions with simpler system designs and reduced cost. Unlike other technologies, LDC-enabled inductive sensing employs low-cost, high-reliability inductors as sensors, which can be located remotely from the IC. By integrating up to four channels in a single IC, the LDC1614 family allows designers to distribute sensors throughout a system, while centralising electronics on fewer PCBs. This can benefit precision linear or rotational sensing and metal detection in a variety of end equipments including white goods, printers, cameras and automotive infotainment consoles.

The LDC1614 family offers;

Multiple, well-matched channels, to enables differential and ratiometric measurements, allowing designers to compensate for environmental and ageing conditions such as temperature, humidity and mechanical drift.

Precision measurement capability provides up to 28-bit resolution; the devices can detect submicron changes in distance.

Wide sensor frequency range: with support of a frequency range of 1 kHz to 10 MHz, designers have flexibility to use many types of inductors as sensors. This frequency range also enables use of very small PCB coils, which reduces overall sensing solution cost and size.

Low system power: powered by a 3.3-V supply, the LDC1614 family consumes approximately 6.9 mW during standard operation and 0.12 mW while in shutdown mode.

High reliability: contactless sensing is immune to nonconductive contaminants, such as oil, dirt and dust, which can shorten equipment life.

The LDC1614EVM evaluation board, which includes the ultra-low power MSP430F5528 microcontroller (MCU), is available to evaluate the LDC1614 for $29. System designers can build sensors with TI's WEBENCH Inductive Sensing Designer. This online tool simplifies sensor coil design based on application and system requirements. The optimised design can be exported to a variety of computer-aided design programs to quickly incorporate the sensor coil into an overall system layout.

The 16-button keypad reference design (TIDA-00509) uses the LDC1314 in a multiplexed inductive keypad system, which