The AD7745/AD7746 are a high resolution, Σ-Δ capacitance-to-digital converter (CDC). The capacitance to be measured is connected directly to the device inputs. The architecture fea-tures inherent high resolution (24-bit no missing codes, up to 21-bit effective resolution), high linearity (±0.01%), and high accuracy (±4 fF factory calibrated). The AD7745/AD7746 capacitance input range is ±4 pF (changing), while it can accept up to 17 pF common-mode capacitance (not changing), which can be balanced by a programmable on-chip, digital-to-capacitance converter (CAPDAC).
The AD7745 has one capacitance input channel, while the AD7746 has two channels. Each channel can be configured as single-ended or differential. The AD7745/AD7746 are designed for floating capacitive sensors. For capacitive sensors with one plate connected to ground, the AD7747 is recommended.
The parts have an on-chip temperature sensor with a resolution of 0.1°C and accuracy of ±2°C. The on-chip voltage reference and the on-chip clock generator eliminate the need for any external components in capacitive sensor applications. The parts have a standard voltage input, which together with the differential reference input allows easy interface to an external temperature sensor, such as an RTD, thermistor, or diode.
The AD7745/AD7746 have a 2-wire, I2C-compatible serial interface. Both parts can operate with a single power supply from 2.7 V to 5.25 V. They are specified over the automotive temperature range of –40°C to +125°C and are housed in a 16-lead TSSOP package.
Automotive, Industrial and Medical Systems for:
The board has a USB port that is by default used to power the board. To power the converter chip, depending on your controller logic level, you need to install a jumper in either the 3.3V or 5V positions of AVDD select header LK1.
Once you've verified that the chip is powered correctly by measuring the AVDD-GND test points, you may proceed to connecting the SDA and SCL lines to your controller. Male pin headers are available at LK2.8 and LK2.6 respectively.
Go to the
no-OS/projects/ad7746-ebz directory and follow the build instructions below.
Clone NO-OS with the
git clone --recursive https://github.com/analogdevicesinc/no-OS
If however you've already cloned NO-OS without the
--recursive flag, you may initialize all the submodules in an existing NO-OS clone with:
git submodule update --recursive --init
Prior to building a no-OS project, it is required to set up some environment variables so that the build process may find the necessary tools (compiler, linker, SDK etc.).
Use the following commands to prepare your environment for building no-OS projects:
Go in the project directory that should be built.
The build process creates a build directory in the project folder:
build ├── app ├── bsp ├── obj ├── release.elf └── tmp
.hex file has been generated, make sure the board is powered on, JTAG cable connected and use the following commands to upload the program to the board or debug.
Uploading the binary to target is generically achieved with:
$ make run
Use the following command to launch the SDK associated to the used platform in order to be able to debug graphically by clicking the debug button:
$ make sdkopen
Fore more details about the available make rules, check out this page.
The demo application uses the stdout/stin over UART for user interaction. Thus you need to set up a serial terminal with the
UART_BAUDRATE specified in the
Connect the serial terminal, run
make run from the project folder and you should see the following demo application that you can interact with by hitting ENTER on the keyboard and by following the instructions:
[INIT] AD7746 initialization ok. [CALIB] 1. Remove the ruler and press ENTER. [CALIB] 2. Place ruler to 51mm (2inch) and press ENTER. [DEMO] Move the ruler around, its position will is read and displayed every 2 seconds. Position: 51 mm, Temperature: 23 *C Position: 50 mm, Temperature: 23 *C Position: 67 mm, Temperature: 23 *C Position: 67 mm, Temperature: 23 *C Position: 67 mm, Temperature: 23 *C Position: 67 mm, Temperature: 23 *C Position: 67 mm, Temperature: 23 *C Position: 47 mm, Temperature: 23 *C Position: 37 mm, Temperature: 23 *C Position: 34 mm, Temperature: 23 *C Position: 34 mm, Temperature: 23 *C Position: 27 mm, Temperature: 23 *C Position: 27 mm, Temperature: 23 *C
A legacy version of this driver and instructions for a Renesas microcontroller may be found at this link.