AD5678_15 datasheet(18/28 Pages) AD | On-Chip Reference in 14-Lead TSSOP

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AD5678

Rev. C | Page 18 of 28

TERMINOLOGY

Relative Accuracy

For the DAC, relative accuracy, or integral nonlinearity (INL), is

a measure of the maximum deviation in LSBs from a straight

line passing through the endpoints of the DAC transfer

function. Figure 5, Figure 7, and Figure 9 show plots of typical

INL vs. code.

Differential Nonlinearity

Differential nonlinearity (DNL) is the difference between the

measured change and the ideal 1 LSB change between any two

adjacent codes. A specified differential nonlinearity of ±1 LSB

maximum ensures monotonicity. This DAC is guaranteed mono-

tonic by design. Figure 6, Figure 8, and Figure 10 show plots of

typical DNL vs. code.

Offset Error

Offset error is a measure of the difference between the actual

VOUT and the ideal VOUT, expressed in millivolts in the linear

region of the transfer function. Offset error is measured on the

AD5678 with Code 512 loaded into the DAC register. It can be

negative or positive and is expressed in millivolts.

Zero-Code Error

Zero-code error is a measure of the output error when zero

code (0x0000) is loaded into the DAC register. Ideally, the

output should be 0 V. The zero-code error is always positive in

the AD5678, because the output of the DAC cannot go below 0 V.

It is due to a combination of the offset errors in the DAC and

output amplifier. Zero-code error is expressed in millivolts.

Figure 18 shows a plot of typical zero-code error vs.

temperature.

Gain Error

Gain error is a measure of the span error of the DAC. It is the

deviation in slope of the DAC transfer characteristic from the

ideal, expressed as a percentage of the full-scale range.

Zero-Code Error Drift

Zero-code error drift is a measure of the change in zero-code

error with a change in temperature. It is expressed in μV/°C.

Gain Error Drift

Gain error drift is a measure of the change in gain error with

changes in temperature. It is expressed in (ppm of full-scale

range)/°C.

Full-Scale Error

Full-scale error is a measure of the output error when full-scale

code (0xFFFF) is loaded into the DAC register. Ideally, the

output should be VDD − 1 LSB. Full-scale error is expressed as a

percentage of the full-scale range. Figure 17 shows a plot of

typical full-scale error vs. temperature.

Digital-to-Analog Glitch Impulse

Digital-to-analog glitch impulse is the impulse injected into the

analog output when the input code in the DAC register changes

state. It is normally specified as the area of the glitch in nV-s

and is measured when the digital input code is changed by

1 LSB at the major carry transition (0x7FFF to 0x8000). See

Figure 34.

DC Power Supply Rejection Ratio (PSRR)

PSRR indicates how the output of the DAC is affected by changes

in the supply voltage. PSRR is the ratio of the change in VOUT to

a change in VDD for full-scale output of the DAC. It is measured

in decibels. VREF is held at 2 V, and VDD is varied ±10%.

DC Crosstalk

DC crosstalk is the dc change in the output level of one DAC in

response to a change in the output of another DAC. It is measured

with a full-scale output change on one DAC (or soft power-down

and power-up) while monitoring another DAC. It is expressed

in microvolts.

DC crosstalk due to load current change is a measure of the

impact that a change in load current on one DAC has to another

DAC kept at midscale. It is expressed in microvolts per milliamp.

Reference Feedthrough

Reference feedthrough is the ratio of the amplitude of the signal

at the DAC output to the reference input when the DAC output

is not being updated (that is, LDAC is high). It is expressed in

decibels.

Channel-to-Channel Isolation

Channel-to-channel isolation is the ratio of the amplitude of the

signal at the output of one DAC to a sine wave on the reference

input of another DAC. It is measured in decibels.

Digital Feedthrough

Digital feedthrough is a measure of the impulse injected into

the analog output of a DAC from the digital input pins of the

device, but is measured when the DAC is not being written to

(SYNC held high). It is specified in nV-s and measured with a

full-scale change on the digital input pins, that is, from all 0s to

all 1s or vice versa.

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