DAC8564 datasheet(25/51 Pages) TI2

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DAC

REF(+)

ResistorString

REF( )

REF

OUTX

62kW

50kW

OUTX + 2

REFL

) (VREFH * VREFL)

65536

REF

DIVIDER

ToOutputAmplifier

(2xGain)

DAC8565

www.ti.com

SBAS411C

– JUNE 2007 – REVISED MARCH 2011

THEORY OF OPERATION

DIGITAL-TO-ANALOG CONVERTER (DAC)

code loaded into the DAC register determines at

which node on the string the voltage is tapped off to

The DAC8565 architecture consists of a string DAC

be fed into the output amplifier by closing one of the

followed by an output buffer amplifier. Figure 92

switches connecting the string to the amplifier. It is

shows a block diagram of the DAC architecture.

monotonic because it is a string of resistors.

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.

(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.

DATA FORMAT

The data format can be straight binary or two

’s

complement.

Table

illustrates

the

differences

between USB (unsigned straight binary) and BTC

(binary two

’s complement) data formats.

Table 1. USB and BTC Codes

USB CODE

BTC CODE

DESCRIPTION

FFFFh

7FFFh

+Full-Scale

– 1LSB

Figure 93. Resistor String

...

8001h

0001h

Midscale + 1LSB

8000h

0000h

Midscale

OUTPUT AMPLIFIER

7FFFh

FFFFh

Midscale

– 1LSB

The output buffer amplifier is capable of generating

...

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

0000h

8000h

Zero Scale

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

RESISTOR STRING

the Typical Characteristics. The slew rate is 2.2V/

μs,

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

with a full-scale settling time of 8

μs with the output

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

unloaded.

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