touch screen controller
Part Number Product Desccription Datasheet Contacts
KTF7792 12-Bit ADC with 4-wire resistive touch screen interface with clock speed up to 1 MHz datasheet sales@icdidik.com
KTF7793 12-Bit ADC with 4-wire resistive touch screen interface with clock speed up to 2 MHz  datasheet

Features
  • 12-Bit ADC with 4-wire resistive touch screen interface
  • 125 kSPS sampling rate
  • Low power dissipation – 1.5 mW
  • Ratio-metric conversion capability
  • Shutdown feature
  • Flexible serial interface
  • Auxiliary inputs
  • 2.7 V to 5 V supply

Applications
  • PDA’s
  • Touch screen monitors
  • Hand held devices

Detail Description
The KTF7793 is a SAR architecture 12-Bit ADC with support circuitry and interface for touch screen controller application. It operates on a 2.7V to 5.5V single supply and consumes about 400 μA supply current when operating on a 2MHz external clock. The output throughput rate is a maximum of 125 kSPS for the A Grade and 60 kSPS for the B Grade.

The ADC is composed of a high performance capacitive DAC and a comparator along with SAR control logic and resistor string segment. The reference input drives the resistor string directly and has an input resistance of around 32 kΩ.

The KTF7793 comes complete with a high performance differential CMOS sample and hold amplifier made up by the capacitive DAC and a low resistance input multiplexer that allows ratiometric or absolute sensing of the resistive touch screen.

There is shutdown capability which is active between conversions when CSB is high. The converter will shut down to under 10 μA of supply current.There is also a Pen Interrupt feature which is active with PD0 control bit. When this is active the X+ input is live and when the touch screen is touched the PENB signal goes active to initiate a convert command for the micro-controller.

Application Information
Analog Input

The KTF7793 has a 4-to-1 multiplexer at its analog inputs. The configuration of this multiplexer is controlled by the serial input control word. As seen in the block diagram this input multiplexer can be configured to read either the X+ input, the Y+ input or one of the auxilliary inputs. An additional bank of switches also configures the driving for the resistive ladder while the input is being sampled and the connection for the reference input of the ADC.

In the single ended configuration the touch screen is connected to VDD and the ADC reference is connected to the REF pin. In the ratio-metric mode both the ADC reference input and the touch screen ladder are connected to VDD through on board switches. This would be a more accurate method for measurement since the touch screen and the ADC are being driven exactly by the same reference voltage.

The KTF7793 uses the CLK as the external clock and this controls all the transfer of information to and from the ADC.

One complete conversion cycle of the KTF7793 will take 24 clock cycles. As CSB is pulled low this initiates a conversion cycle. The ADC looks for a start bit (high) on the DIN pin. As this is detected the next 7 clock cycles are used to clock in 7 the input control bits. On the falling edge of the 9th clock pulse the output data is clocked out and can be read in on the next rising edge. Date is clocked out MSB. The 21st clock rising edge can be used to read in the LSB and then three zeros are clocked out on the trailing 3 cycles. This will complete 24 bits of clock pulses for each conversion.

Package Information

16 LEAD QSOP STANDARD PACKAGE

Overview
The KTF7793, is a 12-bit 125 kSPS through put rate Analog-to-Digital Sampling Converter. It includes low on resistance switches to drive resistive touch screens. Absolute or ratio-metric measurements are possible and two auxiliary inputs are also included.