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THEORY OF OPERATION

D/A SECTION

_

+

Resistor String

Ref+

Ref-

DAC Register

50 kW

50 kW

GND

70 kW

V

OUT

D

256

RESISTOR STRING

To Output

Amplifier

R

R

R

R

GND

Output Amplifier

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DAC5574

SLAS407 – DECEMBER 2003

The architecture of the DAC5574 consists of a string DAC followed by an output buffer amplifier. Figure 27

shows a generalized block diagram of the DAC architecture.

Figure 27. R-String DAC Architecture

The input coding to the DAC5574 is unsigned binary, which gives the ideal output voltage as:

Where D = decimal equivalent of the binary code that is loaded to the DAC register; it can range from 0 to 255.

The resistor string section is shown in Figure 28. It is basically a divide-by-2 resistor, followed by a string of

resistors, each of value R. The code loaded into the DAC register determines at 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. Because the architecture consists of a string of resistors, it is specified monotonic.

Figure 28. Typical Resistor String

The output buffer is a gain-of-2 noninverting amplifiers, capable of generating rail-to-rail voltages on its output,

The source and sink capabilities of the output amplifier can be seen in the typical curves. The slew rate is 1 V/µs

with a half-scale settling time of 6µs with the output unloaded.

I

January 2000). The bus consists of a data line (SDA) and a clock line (SCL) with pullup structures. When the bus

is idle, both SDA and SCL lines are pulled high. All the I

open drain I/O pins, SDA and SCL. A master device, usually a microcontroller or a digital signal processor,

controls the bus. The master is responsible for generating the SCL signal and device addresses. The master also

generates specific conditions that indicate the START and STOP of data transfer. A slave device receives and/or

transmits data on the bus under control of the master device.

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