This is an old revision of the document!
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 goal of this project (Microcontroller No-OS) is to be able to provide reference projects for lower end processors, which can't run Linux, or aren't running a specific operating system, to help those customers using microcontrollers with ADI parts. Here you can find a generic driver which can be used as a base for any microcontroller platform and also specific drivers for Renesas platforms.
The driver contains two parts:
The Communication Driver has a standard interface, so the AD7746 driver can be used exactly as it is provided.
There are three functions which are called by the AD7746 driver:
I2C driver architecture
The following functions are implemented in this version of AD7746 driver:
|unsigned char AD7746_Init(void)||Initializes the I2C communication peripheral.|
|void AD7746_Write(unsigned char subAddr, unsigned char* dataBuffer, unsigned char bytesNumber)||Writes data into AD7746 registers, starting from the selected register address pointer.|
|void AD7746_Read(unsigned char subAddr, unsigned char* dataBuffer, unsigned char bytesNumber)||Reads data from AD7746 registers, starting from the selected register address pointer.|
|void AD7746_Reset(void)||Resets the AD7746.|
|unsigned long AD7746_GetVTData(void)||Waits until a conversion on a voltage/temperature channel has been finished and returns the output data.|
|unsigned long AD7746_GetCapData(void)||Waits until a conversion on a capacitive channel has been finished and returns the output data.|
This section contains a description of the steps required to run the AD7746 demonstration project on a Renesas RL78G13 platform.
An EVAL-AD7746EBZ has to be interfaced with the Renesas Demonstration Kit (RDK) for RL78G13:
EVAL-AD7746EBZ LK2 connector Pin AVDD → YRDKRL78G13 J11 connector Pin 6 EVAL-AD7746EBZ LK2 connector Pin SDA → YRDKRL78G13 J6 connector Pin 23 EVAL-AD7746EBZ LK2 connector Pin SCL → YRDKRL78G13 J11 connector Pin 9 EVAL-AD7746EBZ LK2 connector Pin AGND → YRDKRL78G13 J11 connector Pin 5
With the Applilet3 for RL78G13 tool the following peripherals have to be configured:
Choose to generate the Transmit/receive function for the CSI10 and configure the interface with the following settings:
Configure TM00 as an interval timer:
Disable the watchdog timer:
The reference project configures the device to read data from the internal temperature sensor and from the second capacitive channel (on the AD7746 evaluation board, the second capacitive channel is used with the on-board capacitive length sensor demo).
First, the part has to be calibrated to the length of the ruler:
The part is now calibrated to the length of the ruler.
After the calibration is done, the temperature and the length are displayed on the screen. The length value changes as the user slides the ruler on the evaluation board.
This section presents the steps for developing a software application that will run on the Renesas Demo Kit for RL78G13 for controlling and monitoring the operation of the ADI part.
Two software applications have to be used: Applilet3 for RL78G13 (a tool that automatically generates device drivers for MCU peripheral functions) and IAR Embedded Workbench for Renesas RL78 (the integrated development environment).