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TSC2200IRHBR Arkusz danych(PDF) 11 Page - Burr-Brown (TI) |
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TSC2200IRHBR Arkusz danych(HTML) 11 Page - Burr-Brown (TI) |
11 / 40 page 11 www.ti.com TSC2200 SBAS191F FIGURE 5. Ideal Input Voltages and Output Codes. FIGURE 6. PENIRQ Functional Block Diagram. 0V FS = Full-Scale Voltage = V REF (1) 1LSB = V REF (1)/4096 FS – 1LSB 11...111 11...110 11...101 00...010 00...001 00...000 1LSB NOTES: (1) Reference voltage at converter: +REF – (–REF). See Figure 4. (2) Input voltage at converter, after multiplexer: +IN – (–IN). See Figure 4. Input Voltage(2) (V) V DD V DD 50k Ω ON Y+ or X+ Drivers On, or TEMP1, TEMP2 Measurements Activated Y+ X+ Y– HIGH Except when TEMP1, TEMP2 Activated PENIRQ TEMP2 TEMP1 TEMP DIODE A unique configuration of low on-resistance switches allows an unselected A/D converter input channel to provide power and an accompanying pin to provide ground for driving the touch panel. By maintaining a differential input to the con- verter and a differential reference input architecture, it is possible to negate errors caused by the driver switch on- resistances. The A/D converter is controlled by an A/D Converter Control Register. Several modes of operation are possible, depend- ing upon the bits set in the control register. Channel selec- tion, scan operation, averaging, resolution, and conversion rate may all be programmed through this register. These modes are outlined in the sections below for each type of analog input. The results of conversions made are stored in the appropriate result register. Data Format The TSC2200 output data is in Straight Binary format, as shown in Figure 5. This figure shows the ideal output code for the given input voltage and does not include the effects of offset, gain, or noise. Reference The TSC2200 has an internal voltage reference that can be set to 1.25V or 2.5V, through the Reference Control Register. The internal reference voltage is only used in the single- ended mode for battery monitoring, temperature measure- ment, and for utilizing the auxiliary inputs. Optimal touch screen performance is achieved when using a ratiometric conversion, thus all touch screen measurements are done automatically in the differential mode. An external reference can also be applied to the VREF pin, and the internal refer- ence can be turned off. Variable Resolution The TSC2200 provides three different resolutions for the A/D converter: 8-, 10-, or 12-bits. Lower resolutions are often practical for measurements such as touch pressure. Perform- ing the conversions at lower resolutions reduces the amount of time it takes for the A/D converter to complete its conversion process, which lowers power consumption. Conversion Clock and Conversion Time The TSC2200 contains an internal 8MHz clock, which is used to drive the state machines inside the device that perform the many functions of the part. This clock is divided down to provide a clock to run the A/D converter. The division ratio for this clock is set in the A/D Converter Control Register. The ability to change the conversion clock rate allows the user to choose the optimal value for resolution, speed, and power. If the 8MHz clock is used directly, the A/D converter is limited to 8-bit resolution; using higher resolutions at this speed will not result in accurate conversions. Using a 4MHz conversion clock is suitable for 10-bit resolution; 12-bit resolution requires that the conversion clock run at 1MHz or 2MHz. Regardless of the conversion clock speed, the internal clock will run nominally at 8MHz. The conversion time of the TSC2200 is dependent upon several functions. Although the conversion clock speed plays an important role in the time it takes for a conversion to complete, a certain number of internal clock cycles is needed for proper sampling of the signal. Moreover, additional times, such as the Panel Voltage Stabilization time, can add significantly to the time it takes to perform a conversion. Conversion time can vary depending upon the mode in which the TSC2200 is used. Throughout this data sheet, internal and conversion clock cycles will be used to describe the times that many functions take. In considering the total system design, these times must be taken into account by the user. Touch Detect The pen interrupt (PENIRQ) output function is detailed in Figure 6. While in the power-down mode, the Y– driver is ON and connected to GND and the PENIRQ output is connected to the X+ input. When the panel is touched, the X+ input is |
Podobny numer części - TSC2200IRHBR |
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Podobny opis - TSC2200IRHBR |
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