Touch Screen Digitizer with Direct Battery and Touch-Pressure Measurement
Introduction
The AD7873 is a 12-bit successive-approximation ADC with a synchronous serial interface and low on resistance switches for driving touch screens. The AD7873 operates from a single 2.2 V to 5.25 V power supply and features throughput rates greater than 125 kSPS. The AD7873 features direct battery measurement, temperature measurement and touch-pressure measurement. The AD7873 has an on-board reference of 2.5 V. An external reference can also be applied and can be varied from 1 V to VCC, while the analog input range is from 0 V to VREF. The device includes a shutdown mode that reduces the current consumption to less than 1 µA. This part is available in a 16-lead 0.15" Quarter Size Outline (QSOP) pack-age and a 16-lead Thin Shrink Small Outline (TSSOP) package. (Click here to see QSOP Package Dimensions.)
Also see the AD7843, which is a sister part to the AD7873.
Full data on the AD7873 is available in the AD7873 data sheet available from Analog Devices and should be consulted in conjunction with the EVAL-AD7873CB Technical Note when using the Evaluation Board.
The board has features that allow the user to evaluate all the functions of the AD7873. On-board components include an AD780 which is a pin programmable +2.5 V or +3 V ultra high precision bandgap reference, and two AD713 quad op-amps. There are various link options which are explained in detail on page 2 of the EVAL-AD7873CB Technical Note.
Interfacing to this board is through a 96-way connector. External sockets are provided for the optional, external, DCLK, CS, and DIN inputs; BUSY, DOUT and PENIRQ outputs; VBAT and AUX inputs ; the VIN input and VBIASED output of the bias-up circuit. External inputs are also supplied to allow the user to easily connect a 4-wire touch-screen panel to the X+,X-, Y+, and Y- inputs.
This evaluation board is compatible with the Evaluation Board Controller which is also available from Analog Devices.
Software
Included in the EVAL-AD7873CB evaluation board package is software for controlling and evaluating the performance of the AD7873 when it is operated with the Evaluation Board Controller. The EVAL-AD7873CB Demonstration/Evaluation Software runs under Windows 95, 98, 2000 & NT. The user interface on the PC is via a dedicated program written especially for the EVAL-AD7873.
To download software, select the link below:
- AD7873.zip (zip, 4,584,169 bytes)
Documentation
Technical notes are available in Adobe Acrobat Portable Document Format (PDF).
To download the Technical Note, select the link below:
- EVAL-AD7843CB Technical Note (pdf, 1,912,866 bytes)
For more information on the AD7843 and AD7873 see the Technical Note on
Layout and Grounding Recommendations for Touch Screen Digitizers. (pdf, 53,905 bytes)