DAC8565 datasheet(25/46 Pages) TI

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THEORY OF OPERATION

DIGITAL-TO-ANALOG CONVERTER (DAC)

DAC

REF(+)

ResistorString

REF( )

REF

OUTX

62kW

50kW

OUTX + 2

REFL

) (VREFH * VREFL)

65536

(1)

RESISTOR STRING

REF

DIVIDER

ToOutputAmplifier

(2xGain)

OUTPUT AMPLIFIER

DAC8565

SBAS411A – JUNE 2007 – REVISED NOVEMBER 2007

The DAC8565 architecture consists of a string DAC

followed by an output buffer amplifier. Figure 92

shows a block diagram of the DAC architecture.

Figure 92. DAC8565 Architecture

The input coding to the DAC8565 can be straight

binary or two's complement, 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

to 65535. X represents channel A, B, C, or D.

The resistor string section is shown in Figure 93. It is

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

code loaded into the DAC register determines at

Figure 93. Resistor String

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.

The output buffer amplifier is capable of generating

rail-to-rail voltages on its output, giving an output

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

Ω in parallel with 1000pF to GND. The source and

sink capabilities of the output amplifier can be seen in

the Typical Characteristics. The slew rate is 2.2V/

µs,

with a full-scale settling time of 8

µs with the output

unloaded.

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