DAC101C081CIMK Datasheet, PDF(14/24 Page) National Semiconductor (TI) – 10-Bit Micro Power Digital-to-Analog Converter with an I2C-Compatible Interface

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DAC101C081CIMK Datasheet, PDF (14/24 Pages) National Semiconductor (TI) – 10-Bit Micro Power Digital-to-Analog Converter with an I2C-Compatible Interface

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1.0 Functional Description

1.1 DAC SECTION

The DAC101C081 is fabricated on a CMOS process with an

architecture that consists of switches and resistor strings that

are followed by an output buffer.

For simplicity, a single resistor string is shown in Figure 3.

This string consists of 1024 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 out-

put voltage of:

VOUT = VREF x (D / 1024)

where D is the decimal equivalent of the binary code that is

loaded into the DAC register. D can take on any integer value

between 0 and1023. This configuration guarantees that the

DAC is monotonic.

1.2 OUTPUT AMPLIFIER

The output amplifier is rail-to-rail, providing an output voltage

range of 0V to VA when the reference is VA. All amplifiers,

even rail-to-rail types, exhibit a loss of linearity as the output

approaches the supply rails (0V and VA, 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 VA,

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

capabilities of the amplifier are described in the Electrical Ta-

bles.

The output amplifiers are capable of driving a load of 2 kâ¦ in

parallel with 1500 pF to ground or to VA. The zero-code and

full-scale outputs for given load currents are available in the

Electrical Characteristics Table.

1.3 REFERENCE VOLTAGE

The DAC101C081 uses the supply (VA) as the reference.

With that said, VA must be treated as a reference. The Analog

output will only be as clean as the reference (VA). It is rec-

ommended that the reference be driven by a voltage source

with low output impedance.

The DAC101C085 comes with an external reference supply

pin (VREF). For the DAC101C085, it is important that VREF be

kept as clean as possible.

The Applications section describes a handful of ways to drive

the reference appropriately. Refer to Section 2.1 for details.

30052207

FIGURE 3. DAC Resistor String

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