DAC7678SPW datasheet(41/52 Pages) TI

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DAC7678

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SBAS493A – FEBRUARY 2010 – REVISED AUGUST 2010

PARAMETER DEFINITIONS

With the increased complexity of many different

Full-Scale Error

specifications listed in product data sheets, this

Full-scale error is defined as the deviation of the real

section summarizes selected specifications related to

full-scale output voltage from the ideal output voltage

digital-to-analog converters.

while the DAC register is loaded with the full-scale

code (0xFFF). Ideally, the output should be AVDD – 1

STATIC PERFORMANCE

LSB. The full-scale error is expressed in percent of

full-scale range (%FSR).

Static performance parameters are specifications

such as differential nonlinearity (DNL) or integral

Offset Error

nonlinearity (INL). These are dc specifications and

The offset error is defined as the difference between

provide information on the accuracy of the DAC. They

actual output voltage and the ideal output voltage in

are most important in applications where the signal

the linear region of the transfer function. This

changes slowly and accuracy is required.

difference is calculated by using a straight line

defined by two codes (code 30 and 4050). Since the

Resolution

offset error is defined by a straight line, it can have a

Generally, the DAC resolution can be expressed in

negative or positive value. Offset error is measured in

different forms. Specifications such as IEC 60748-4

mV.

recognize

the

numerical,

analog,

and

relative

resolution. The numerical resolution is defined as the

Zero-Code Error

number of digits in the chosen numbering system

The zero-code error is defined as the DAC output

necessary to express the total number of steps of the

voltage, when all '0's are loaded into the DAC

transfer characteristic, where a step represents both

a digital input code and the corresponding discrete

difference between actual output voltage and ideal

analogue output value. The most commonly-used

output voltage (0V). It is expressed in mV. It is

definition of resolution provided in data sheets is the

primarily caused by offsets in the output amplifier.

numerical resolution expressed in bits.

Gain Error

Least Significant Bit (LSB)

Gain error is defined as the deviation in the slope of

The least significant bit (LSB) is defined as the

the real DAC transfer characteristic from the ideal

smallest value in a binary coded system. The value of

transfer function. Gain error is expressed as a

the LSB can be calculated by dividing the full-scale

percentage of full-scale range (%FSR).

output voltage by 2n, where n is the resolution of the

Full-Scale Error Drift

converter.

Full-scale error drift is defined as the change in

Most Significant Bit (MSB)

full-scale

error

with

change

temperature.

The most significant bit (MSB) is defined as the

Full-scale error drift is expressed in units of µV/°C.

largest value in a binary coded system. The value of

Offset Error Drift

the MSB can be calculated by dividing the full-scale

Offset error drift is defined as the change in offset

output voltage by 2. Its value is one-half of full-scale.

error with a change in temperature. Offset error drift

Relative Accuracy or Integral Nonlinearity (INL)

is expressed in µV/°C.

Relative accuracy or integral nonlinearity (INL) is

Zero-Code Error Drift

defined as the maximum deviation between the real

Zero-code error drift is defined as the change in

transfer function and a straight line passing through

zero-code error with a change in temperature.

the endpoints of the ideal DAC transfer function. INL

Zero-code error drift is expressed in µV/°C.

is measured in LSBs.

Gain Temperature Coefficient

Differential Nonlinearity (DNL)

The gain temperature coefficient is defined as the

Differential nonlinearity (DNL) is defined as the

change in gain error with changes in temperature.

maximum deviation of the real LSB step from the

The gain temperature coefficient is expressed in ppm

ideal 1LSB step. Ideally, any two adjacent digital

of FSR/°C.

codes correspond to output analog voltages that are

exactly one LSB apart. If the DNL is less than 1LSB,

the DAC is said to be monotonic.

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