XPT2046 Ver la hoja de datos (PDF) - Unspecified

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XPT2046

Touch Screen Controller

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XPT2046 Touch Screen Controller

△ V ＝ kT • ln(N ) … … … … … … … … … … （ 1）

q

where:

N is the current ratio = 91.

k = Boltzmann’s constant (1.38054 • 10−23 electron volts/ degrees Kelvin).

q = the electron charge (1.602189 • 10–19 C).

T = the temperature in degrees Kelvin.

This method can provide improved absolute temperature measurement over the first mode at the cost of less

resolution (1.6°C/LSB). The equation for solving for °K is:

°K = q • ΔV …………………………（2）

(k • ln(N ))

where:

ΔV = V (I91) – V (I1) (in mV)

°K = 2.573 °K/mV • ΔV

°C = 2.573 • ΔV(mV) – 273°K

NOTE: The bias current for each diode temperature measurement is only on for 3 clock cycles (during the

acquisition mode) and, therefore, does not add any noticeable increase in power, especially if the temperature

measurement only occurs occasionally.

Battery Measurement

An added feature of the XPT2046 is the ability to monitor the battery voltage on the other side of the voltage

regulator(DC/DC converter), as shown in Figure 10. The battery voltage can vary from 0V to 6V, while

maintaining the voltage to the XPT2046 at 2.7V, 3.3V, etc. The input voltage (VBAT)is divided down by 4 so that

a 5.5V battery voltage is represented as 1.375V to the ADC. This simplifies the multiplexer and control logic. In

order to minimize the power consumption, the divider is only on during the sampling period when A2 = 0, A1 = 1,

and A0 = 0 (see Table 1 for the relationship between the control bits and configuration of the XPT2046).

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

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