XPT2046 查看數據表（PDF） - Unspecified

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产品描述 (功能)

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XPT2046

Touch Screen Controller

Unspecified 

XPT2046 Touch Screen Controller

the differential mode only for the touch screen measurements and command the XPT2046 to remain on (touch

screen drivers ON) and not go into power-down (PD0 = 1). Several conversions are made depending on thes

ettling time required and the XPT2046 data rate. Once the required number of conversions have been made, the

processor commands the XPT2046 to go into its power-down state on the last measurement. This process isr

equired for X-Position,Y-Position, and Z-Position measurements. Option 3 is to operate in the 15

Clock-per-Conversion mode, which overlaps the analog-to-digital conversions and maintains the touch screen

drivers on until commanded to stop by the processor (see Figure 16).

Temperature Measurement

In some applications, such as battery recharging, a measurement of ambient temperature is required. The

temperature measurement technique used in the XPT2046 relies on the characteristics of a semiconductor

junction operating at a fixed current level. The forward diode voltage (VBE) has a well-defined characteristic

versus temperature. The ambient temperature can be predicted in applications by knowing the +25　C value of

the VBE voltage and then monitoring the delta of that voltage as the temperature changes. The XPT2046 offers

two modes of operation. The first mode requires calibration at a known temperature, but only requires a single

reading to predict the ambient temperature. A diode is used (turned on) during this measurement cycle. The

voltage across the diode is connected through the MUX for digitizing the forward bias voltage by the ADC with

an address of A2 = 0, A1 = 0, and A0 = 0 (see Table 1 and Figure 6 for details). This voltage is typically 600mV

at +25　C with a 20　A current through the diode. The absolute value of this diode voltage can vary a few

millivolts.However, the TC of this voltage is very consistent at –2.1mV/　C. During the final test of the end

product, the diode voltage would be stored at a known room temperature, in memory, for calibration purposes by

the user. The result is an equivalent temperature measurement resolution of 0.3　C/LSB (in 12-bit mode).

VCC

TEMP1

TEMP0

MUX

ADC

Figure 9. Functional Block Diagram of Temperature Measurement

The second mode does not require a test temperature calibration, but uses a two-measurement method to eliminate

the need for absolute temperature calibration and for achieving 2　C accuracy. This mode requires a second

conversion with an address of A2 = 1, A1 = 1, and A0 = 1, with a 91 times larger current. The voltage difference

between the first and second conversion using 91 times the bias current is represented by Equation (1):

Copyright©2007, SHENZHEN XPTEK TECHNOLOGY CO.,LTD http://www.xptek.com.cn

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