APT7846 查看數據表（PDF） - Anpec Electronics

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APT7846

Touch Screen Controller

Anpec Electronics 

APT7846

TEMPERATURE MEASUREMENT

The temperature measurement technique used in the

APT7846 relies on the characteristics of a semicon-

ductor junction operation at a fixed current level. The

forward bipolar transistor voltage (VBE ) has a well

defined characteristic versus temperature.

If you got 25°C value of the VBE voltage then mea-

sured ambient temperature to monitor the voltage

variance.

There are two mode to measure temperature. The

Temp 0 requires calibration at a known temperature

, but only requires a single reading to predict the am-

bient temperature. The PENIRQ bipolar transistor is

used during this measurement , the A/D with an ad-

dress of A2=0 , A1=0 and A0=0 (see Table I and

Figure 6). This voltage is typically 600mV at +25°C ,

with a 20µA current through it. The TC of tempera-

ture Temp 0 is very consistent at –2.1 mV/°C. Catch

the bipolar transistor voltage on room temperature ,

in memory , for calibration purposes by the user.

The Temp 1 requires two steps to measure

temperature.

First step read Temp 0 voltage. Second step read

address of A2=1 , A1=1 , and A0=1 , with an 82 times

large current.

The voltage difference between the Temp 0 and

Temp 1 conversion using 82 times the bias.

MUX

A/D

Converter

Current will be represented by kT/q ∗ ln (N) , where N

is the current ratio = 82 , k = Boltzmann’s constant

(1.38054 ∗ 10e–23 electrons volts/degrees Kelvin) ,

q = the electron charge (1.602189 ∗ 10e–19 C) , and

T = the temperature in degrees Kelvin. The resultant

equation for solving for °K is :

°K = q ∗ ∆V / ( k ∗ In ( N ) )

(1)

where , ∆V = V( Ι82 ) – V ( Ι1 ) ( mV )

∴ °K = 2.30 ∆V ( °K / mV )

°C = 2.30 ∆V ( mV ) – 273 °K

BATTERY MEASUREMENT

An added feature of the APT7846 is the ability to

monitor the battery voltage , as shown in Figure7.

The battery voltage can vary from 0.5V to 6V , while

maintaining the voltage to the APT7846 at 2.7V ,

3.3V , etc. The input voltage (VBAT ) is divided down

by 4 so that a 6.0V battery voltage is represented as

1.5V to the ADC. This simplifies the multiplexer and

control logic. In order to minimize the power con-

sumption , the divider is only ON during the samling

of DIN to A2=0 , A1=1 , and A0=0. Tables I and II

show the relationship between the control bits and

configuration of the APT7846.

Battery

0.5V

to

6.0V

DC/DC

Converter

Vcc

VBAT

0.125V to 1.5V

7.5kΩ

2.5kΩ

FIGURE 6. Functional Block Diagram of Tempera- FIGURE 7. Battery Measurement Functional Block

ture Measurement Mode..1/URE

Diagram.

Copyright  ANPEC Electronics Corp.

9

Rev. A.6 - Dec., 2001

www.anpec.com.tw

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