Version 1.0 2-1
Chapter 2
Analog-to-Digital Converter/
Brownout Detector
The LH79524/LH79525 incorporate an analog-to-digital converter (ADC) and implements
a touch screen controller (TSC) and brownout detector with interrupt.
2.1 Theory of Operation
The ADC and TSC incorporate:
• 10-bit ADC with integrated sample and hold, and fully-differential high impedance
signals, and single-ended or ratiometric reference inputs
• A 10-channel multiplexer that routes user-selected inputs to the ADC in single-ended
and ratiometric modes
• A 16-entry × 16-bit-wide FIFO containing the 10-bit ADC output
• Active input matrix provides a bias-and-control network for the touch screen interface
and support functions, which are compatible with industry-standard 4-, 5-, 7-, and 8-wire
touch-sensitive panels
• Pen-down sensing circuit and interrupt generator
• Independently-controlled voltage reference generator
• Conversion automation function to minimize controller interrupt overhead
• Three power modes: Off, Standby, and Run
• Brownout detector with interrupt.
2.1.1 Operational Summary
The ADC is an AMBA-compliant SoC peripheral that connects as a slave to the APB. The
ADC block consists of an 10-channel, 10-bit Analog-to-Digital Converter with integrated
Touch Screen Controller. The complete touch screen interface is achieved by combining
the front-end biasing, control circuitry with analog-to-digital conversion, reference genera-
tion, and digital control. Figure 2-1 shows a block diagram of the ADC.
The ADC has a bias-and-control network that allows correct operation with 4-, 5-, 7-, and
8-wire touch panels. A 16-entry × 16-bit wide FIFO holds a 10-bit ADC output and a 4-bit
tag number. When the screen is touched, it pushes the conductive coating on the cover-
sheet against the coating on the glass, making electrical contact. The voltages produced
are the analog representation of the position touched. The voltage level of the coversheet
is converted continuously by the ADC and monitored by the system.
To Next Page
Loading...