Line Card

AD7877: Touch Screen Controller


【Basic Info】

【Product Feature】

* 4-wire touch screen interface
* LCD noise reduction feature (STOPACQ pin)
* Automatic conversion sequencer and timer
* User-programmable conversion parameters
* On-chip temperature sensor:
−40°C to +85°C
* On-chip 2.5 V reference
* On-chip 8-bit DAC
* 3 auxiliary analog inputs
* 1 dedicated and 3 optional GPIOs
* 2 direct battery measurement channels (0.5 V to 5 V)
* 3 interrupt outputs
* Touch-pressure measurement
Resolution (Bits): 12bit
T-Put Rate: 125kSPS
# Chan: 9
Supply V: Single(+3),Single(+3.3)
Pwr Diss: 3.2mW
Sleep Pwr Diss: 3.6µW
Ain Range: Uni (Vref),Uni 2.5V
Ref: Int/Ext Int/Ext
Product Description: 4-Wire Resistive Touch Screen Controller w/ Noise Reduction, DAC, Conversion Controls, & GPIO


* Personal digital assistants
* Smart hand-held devices
* Touch screen monitors
* Point-of-sale terminals
* Medical devices
* Cell phones
* Pagers


The AD7877 is a 12-bit, successive approximation ADC with a synchronous serial interface and low on resistance switches for driving touch screens. The AD7877 operates from a single 2.7 V to 5.25 V power supply (functional operation to 2.2 V), and features throughput rates of 125 kSPS. The AD7877 features direct battery measurement on two inputs, temperature and touch-pressure measurement.

The AD7877 also has an on-board reference of 2.5 V. When not in use, it 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 of 0 V to VREF. The device includes a shutdown mode that reduces its current consumption to less than 1 µA.

To reduce the effects of noise from LCDs, the acquisition phase of the on-board ADC is controlled via the STOPACQ pin. User-programmable conversion controls include variable acquisition time and first conversion delay. Up to 16 averages can be taken per conversion. There is also an on-board DAC for LCD back-light or contrast control. The AD7877 runs in either slave or master mode using a conversion sequencer and timer. It is ideal for battery-powered systems such as personal digital assistants with resistive touch screens and other portable equipment.

The part is available in a 32-lead lead frame chip scale package (LFCSP), and a 25-ball wafer level chip scale package (WLCSP).