The AD7879/AD7889 are 12-bit successive approximationanalog-to-digital converters (SAR ADCs) with a synchronousserial interface and low on-resistance switches for driving 4-wireresistive touch screens. The AD7879/AD7889 work with a verylow power supply—a single 1.6 V to 3.6 V supply—and feature athroughput rate of 105 kSPS. The devices include a shutdownmode that reduces current consumption to less than 6 μA.
To reduce the effects of noise from LCDs and other sources, theAD7879/AD7889 contain a preprocessing block. Thepreprocessing function consists of a median filter and anaveraging filter. The combination of these two filters provides amore robust solution, discarding the spurious noise in the signaland keeping only the data of interest. The size of both filters isprogrammable. Other user-programmable conversion controlsinclude variable acquisition time and first conversion delay; upto 16 averages can be taken per conversion. The AD7879/AD7889can run in slave mode or standalone (master) mode, using anautomatic conversion sequencer and timer.
The AD7879/AD7889 have a programmable pin that canoperate as an auxiliary input to the ADCs, as a battery monitor,or as a general-purpose input/output (GPIO). In addition, aprogrammable interrupt output can operate in three modes: as ageneral-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 temperaturemeasurement and touch pressure measurement.
The AD7879-1ACBZ-500R7 is available in a 12-ball, 1.6 mm × 2 mm WLCSPand in a 16-lead, 4 mm × 4 mm LFCSP. The AD7889 is availablein a backside coated version of the WLCSP. Both devices supportan SPI interface (AD7879/AD7889) or an I2C interface (AD7879-1/AD7889-1).
Feature
- 4-wire touch screen interface
- 1.6 V to 3.6 V 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
- Interrupt outputs (INT, PENIRQ)
- Touch-pressure measurement
- Wake-up on touch function
- Shutdown mode: 6 μA maximum
- 12-ball, 1.6 mm × 2 mm WLCSP
- 16-lead, 4 mm × 4 mm LFCSP
Applications
- Personal digital assistants
- Smart handheld devices
- Touch screen monitors
- Point-of-sale terminals
- Medical devices
- Cell phones
(Picture: Pinout)
