Touch Screen Digitizer
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 supply, with a throughput rate of 125 kSPS.
The AD7873 features direct battery measurement, temperature measurement, and touch pressure measurement. The AD7873 also has an on-board reference of 2.5 V that can be used for the auxiliary input, battery monitor, and temperature measurement modes. When not in use, the internal reference can be shut down to conserve power. An external reference can also be applied and varied from 1 V to VCC with an analog input range from 0 V to VREF. The device includes a shutdown mode that reduces the current consumption to less than 1 µA.
The AD7873 features on-board switches. This, coupled with low power and high speed operation, makes the device ideal for battery-powered systems with resistive touch screens. The part is available in a 16-lead, 0.15 inch quarter size outline package (QSOP), a 16-lead, thin shrink small outline package (TSSOP), and a 16-lead, lead frame chip scale package (LFCSP).
- Ratiometric conversion mode available, eliminating errors due to on-board switch resistances.
- On-board temperature sensor: −40°C to +85°C.
- Battery monitor input.
- Touch pressure measurement capability.
- Low power consumption of 1.37 mW maximum with the reference off, or 2.41 mW typical with the reference on, at 125 kSPS and VCC at 3.6 V.
- Package options include 4 mm × 4 mm LFCSP.
- Analog input range from 0 V to VREF.
- Versatile serial I/O ports.
- Personal digital assistants
- Smart hand-held devices
- Touch screen monitors
- Point-of-sale terminals
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
The PDA Challenge—Met by the AD7873 Resistive-Touch-Screen Controller ADC
(Analog Dialogue, Vol. 35, No. 4, August-September, 2001)
MS-2210: Designing Power Supplies for High Speed ADC
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