DAC7568 datasheet(30/58 Pages) TI

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THEORY OF OPERATION

DIGITAL-TO-ANALOG CONVERTER (DAC)

DAC

REF(+)

ResistorString

REF( )

REF

OUTX

62kW

50kW

OUT

Gain

REF

(1)

REF

DIVIDER

ToOutputAmplifier

(2xGain)

OUTPUT AMPLIFIER

RESISTOR STRING

DAC7568

DAC8168

DAC8568

SBAS430A – JANUARY 2009 – REVISED APRIL 2009 ..................................................................................................................................................... www.ti.com

The DAC7568, DAC8168, and DAC8568 architecture

consists of eight string DACs each followed by an

output buffer amplifier. The devices include an

internal 2.5V reference with 2ppm/°C temperature

drift performance, and offer either 5V or 2.5V full

scale output voltage. Figure 120 shows a principal

block diagram of the DAC architecture.

Figure 120. Device Architecture

The input coding to the DAC7568, DAC8168, and

DAC8568 is straight binary, so the ideal output

voltage is given by Equation 1:

Where:

DIN = decimal equivalent of the binary code that

is loaded to the DAC register. It can range from 0

Figure 121. Resistor String

to 4095 for DAC7568 (12 bit), 0 to 16,383 for

DAC8168 (14 bit), and 0 to 65535 for DAC8568

(16 bit).

n = resolution in bits; either 12 (DAC7568), 14

(DAC8168) or 16 (DAC8568)

The output buffer amplifier is capable of generating

rail-to-rail voltages on its output, giving a maximum

Gain = 1 for A/B grades or 2 for C/D grades.

output range of 0V to AVDD. It is capable of driving a

load of 2k

Ω in parallel with 3000pF to GND. The

source and sink capabilities of the output amplifier

The resistor string section is shown in Figure 121. It

can be seen in the Typical Characteristics. The

is simply a string of resistors, each of value R. The

typical slew rate is 0.75V/

µs, with a typical full-scale

code loaded into the DAC register determines at

settling time of 5

µs with the output unloaded.

which node on the string the voltage is tapped off to

be fed into the output amplifier by closing one of the

switches connecting the string to the amplifier. It is

monotonic because it is a string of resistors.

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