Datasheet

To Output Amplifier

DAC082S085

SNAS365F –MAY 2006–REVISED MARCH 2013

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Functional Description

DAC SECTION

The DAC082S085 is fabricated on a CMOS process with an architecture that consists of switches and resistor

strings that are followed by an output buffer. The reference voltage is externally applied at V

REFIN

and is shared

by both DACs.

For simplicity, a single resistor string is shown in Figure 29. This string consists of 256 equal valued resistors

with a switch at each junction of two resistors, plus a switch to ground. The code loaded into the DAC register

determines which switch is closed, connecting the proper node to the amplifier. The input coding is straight

binary with an ideal output voltage of:

OUTA,B

= V

REFIN

x (D / 256)

where

• D is the decimal equivalent of the binary code that is loaded into the DAC register. (D can take on any value

between 0 and 255. This configuration ensures that the DAC is monotonic.) (2)

Figure 29. DAC Resistor String

OUTPUT AMPLIFIERS

The output amplifiers are rail-to-rail, providing an output voltage range of 0V to V

when the reference is V

. All

amplifiers, even rail-to-rail types, exhibit a loss of linearity as the output approaches the supply rails (0V and V

in this case). For this reason, linearity is specified over less than the full output range of the DAC. However, if the

reference is less than V

, there is only a loss in linearity in the lowest codes. The output capabilities of the

amplifier are described in the Electrical Tables.

The output amplifiers are capable of driving a load of 2 kΩ in parallel with 1500 pF to ground or to V

. The zero-

code and full-scale outputs for given load currents are available in the Electrical Characteristics.

REFERENCE VOLTAGE

The DAC082S085 uses a single external reference that is shared by both channels. The reference pin, V

REFIN

, is

not buffered and has an input impedance of 60 kΩ. It is recommended that V

REFIN

be driven by a voltage source

with low output impedance. The reference voltage range is 1.0V to V

, providing the widest possible output

dynamic range.

Product Folder Links: DAC082S085