Line Card

AD7879/7889: Low Voltage Controller for Touch Screens

 2009-06-12

【Basic Info】

【Product Feature】

* 4-wire touch screen interface
* 1.6V to 3.6V operation
* Median and averaging filter to reduce noise
* Automatic conversion sequencer and timer
* User-programmable conversion parameters
* Auxiliary analog input /Battery Monitor (0.5 V to 5 V)
* 1 Optional GPIO
Resolution (Bits): 12bit
T-Put Rate: 105kSPS
# Chan: 6
Supply V: Single(+2.7),Single(+3),Single(+3.3)
Pwr Diss: 2.3mW
Interface: I²C/Ser 2-Wire,Ser,SPI
Ain Range: Uni Vdd
SNR (dB): n/a
Pkg Type: CSP

【Application】

• Personal digital assistants
• Smart hand-held devices
• Touch screen monitors
• Point-of-sales terminals
• Medical devices
• Cell phones

【Overview】

The AD7879/AD7889 are 12-bit successive approximation analog-to-digital converters (SAR ADCs) with a synchronous serial interface and low on-resistance switches for driving 4-wire resistive touch screens. The AD7879/AD7889 work with a very low power supply–a single 1.6 V to 3.6 V supply–and feature throughput rates of 105 kSPS. The devices include a shutdown mode that reduces current consumption to less than 6 μA.

To reduce the effects of noise from LCDs and other sources, the AD7879/AD7889 contain a preprocessing block. The prepro-cessing function consists of a median filter and an averaging filter. The combination of these two filters provides a more robust solution, discarding the spurious noise in the signal and keeping only the data of interest. The size of both filters is programmable. Other user-programmable conversion controls include variable acquisition time and first conversion delay; up to 16 averages can be taken per conversion. The AD7879/AD7889 can run in slave mode or standalone (master) mode, using an automatic conversion sequencer and timer.

The AD7879/AD7889 have a programmable pin that can operate as an auxiliary input to the ADC, as a battery monitor, or as a GPIO. In addition, a programmable interrupt output can operate in three modes: as a general-purpose interrupt to signal when new data is available (DAV), as an interrupt to indicate when limits are exceeded (INT), or as a pen-down interrupt when the screen is touched (PENIRQ). The AD7879/AD7889 offer temp-erature measurement and touch-pressure measurement.

The AD7879 is available in a 12-ball, 1.6 mm × 2 mm WLCSP and in a 16-lead, 4 mm × 4 mm LFCSP. The AD7889 is available in a backside-coated version of the WLCSP. Both parts support an SPI interface (AD7879/AD7889) or an I2C® interface (AD7879-1/AD7889-1).