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AD7879 Low Voltage Controller for Touch Screens

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 a throughput rate 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 preprocessing 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 ADCs, as a battery monitor, or as a general-purpose input/output (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 temperature 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 devices support an SPI interface (AD7879/AD7889) or an I2C interface (AD7879-1/ AD7889-1).

Applications

• Personal digital assistants
• Smart handheld devices
• Touch screen monitors
• Point-of-sale terminals
• Medical devices
• Cell phones

Data Sheets

Application Notes

Order Information

Evaluation Boards

Reference Materials

• Technical Articles：MS-2210: Designing Power Supplies for High Speed ADC