TSC2000IPW datasheet(32/34 Pages) TI

32 / 34 page

www.ti.com

TSC2000

SBAS257

FIGURE 27. D/A Converter Configuration.

FIGURE 28. D/A Converter Output Current Range versus

RRNG Resistor Value.

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

10k

100k

10M

100M

ARNG Resistor (

Ω)

D/A Converter

V+

BIAS

OUT

ARNG

RRNG

8 Bits

OPERATION—D/A CONVERTER

The TSC2000 has an on-board 8-bit D/A converter, config-

ured as shown in Figure 27. This configuration yields a

current sink (AOUT) controlled by the value of a resistor

connected between the ARNG pin and ground. The D/A

converter has a control register, which controls whether or

not the converter is powered up. The 8-bit data is written to

the D/A converter through the D/A converter data register.

This circuit is designed for flexibility in the output voltage at the

VBIAS point shown in Figure 27 to accommodate the widely

varying requirements for LCD contrast control bias. V+ can be

a higher voltage than the supply voltage for the TSC2000. The

only restriction is that the voltage on the AOUT pin can never go

above the absolute maximum ratings for the device, and

should stay above 1.5V for linear operation.

The D/A converter has an output sink range which is limited to

1mA. This range can be adjusted by changing the value of

RRNG shown in Figure 27. As this D/A converter is not

designed to be a precision device, the actual output current

range can vary as much as

±20%. Furthermore, the current

output will change due to variations in temperature; the D/A

converter has a temperature coefficient of approximately

–2

µA/°C. To set the full-scale current, RRNG can be deter-

mined from the graph shown in Figure 28.

For example, consider an LCD that has a contrast control

voltage VBIAS that can range from 2V to 4V, that draws 400µA

when used, and an available +5V supply. Note that this is

higher than the TSC2000 supply voltage, but it is within the

absolute maximum ratings.

The maximum VBIAS voltage is 4V, and this occurs when the

D/A converter current is 0, so only the 400

µA load current

ILOAD will be flowing from 5V to VBIAS. This means 1V will be

dropped across R1, so R1 = 1V/400µA = 2.5kΩ.

The minimum VBIAS is 2V, which occurs when the D/A

converter current is at its full scale value, IMAX. In this case,

5V – 2V = 3V will be dropped across R1, so the current

through R1 will be 3V/2.5K = 1.2mA. This current is

IMAX + ILOAD = IMAX + 400uA, so IMAX must be set to 800µA.

Looking at Figure 28, this means that RRNG should be

around 1M

Ω.

Since the voltage at the AOUT pin should not go below 1.5V,

this limits the voltage at the bottom of R2 to be 1.5V

minimum; this occurs when the D/A converter is providing its

maximum current, IMAX. In this case, IMAX +ILOAD flows through

R1, and IMAX flows through R2. Thus,

R2IMAX + R1(IMAX + ILOAD) = 5V – 1.5V = 3.5V

We already have found R1 = 2.5kΩ, IMAX = 800µA,

ILOAD = 400µA, so we can solve this for R2 and find that it

should be 625

Ω.

TSC2000IPW 数据表(PDF) 32 Page - Texas Instruments

TSC2000IPW 数据表(HTML) 32 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

数据表下载