AD7877:  Touch Screen Controller

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 ...More

AD7877:  Touch Screen Controller

Product Description

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).

Applications

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

    • Features

    • 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

    Diagrams

    AD7877 Diagram
    Functional Block Diagram for AD7877

    Specifications

    Resolution (Bits) 12bit
    T-Put Rate 125kSPS
    # Chan 9
    Supply V Single(+3),Single(+3.3)
    Pwr Diss (max) 3.2mW
    Interface Ser
    Ain Range Uni (Vref),Uni 2.5V
    SNR (dB) n/a
    Pkg Type CSP

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