®

DAC707/708/709

6

DISCUSSION OF

SPECIFICATIONS

DIGITAL INPUT CODES

For bipolar operation, the DAC707/708/709 accept positive-

true binary two’s complement input code. For unipolar

operation (DAC708/709 only) the input code is positive-true

straight-binary provided that the MSB input is inverted with

an external inverter. See Table I.

the MSB must be inverted). This code corresponds to zero

volts (DAC707 and DAC709) or zero milliamps (DAC708)

at the analog output. The maximum change in offset at t

MIN

or t

by the temperature change. This drift is expressed in FSR/

°C.

SETTLING TIME

Settling time of the D/A is the total time required for the

analog output to settle within an error band around its final

value after a change in digital input. Refer to Figure 1 for

typical values for this family of products.

FIGURE 1. Final-Value Error Band Versus Full-Scale Range

Settling Time.

Voltage Output

Settling times are specified to

±0.003% of FSR (±1/2LSB

for 14 bits) for two input conditions: a full-scale range

change of 20V (

±10V) or 10V (±5V or 0 to 10V) and a 1LSB

change at the “major carry”, the point at which the worst-

case settling time occurs. (This is the worst-case point since

all of the input bits change when going from one code to the

next.)

Current Output

Settling times are specified to

±0.003% of FSR for a full-

scale range change for two output load conditions: one for

10

Ω to 100Ω and one for 1000Ω. It is specified this way

because the output RC time constant becomes the dominant

factor in determining settling time for large resistive loads.

COMPLIANCE VOLTAGE

Compliance voltage applies only to current output models. It

is the maximum voltage swing allowed on the output current

pin while still being able to maintain specified accuracy.

POWER SUPPLY SENSITIVITY

Power supply sensitivity is a measure of the effect of a

change in a power supply voltage on the D/A converter

ANALOG OUTPUT

Digital

Binary Two's Complement

Input

(DAC708/709 only; connected

(Bipolar operation;

Codes

for Unipolar operation)

all models)

+Full Scale

Zero

Zero

+Full Scale

–1LSB

+1/2 Full Scale

–Full Scale

NOTES: (1) MSB must be inverted externally. (2) Assumes MSB is inverted

externally.

TABLE I. Digital Input Codes.

ACCURACY

Linearity

This specification describes one of the most important mea-

sures of performance of a D/A converter. Linearity error is

the deviation of the analog output from a straight line drawn

through the end points (–Full Scale point and +Full Scale

point).

Differential Linearity Error

Differential Linearity Error (DLE) of a D/A converter is the

deviation from an ideal 1LSB change in the output when the

input changes from one adjacent code to the next. A differ-

ential linearity error specification of

±1/2LSB means that the

output step size can be between 1/2LSB and 3/2LSB when

the input changes between adjacent codes. A negative DLE

specification of –1LSB maximum (–0.006% for 14-bit reso-

lution) insures monotonicity.

Monotonicity

Monotonicity assures that the analog output will increase or

remain the same for increasing input digital codes. The

DAC707/708/709 are specified to be monotonic to 14 bits

over the entire specification temperature range.

DRIFT

Gain Drift

Gain Drift is a measure of the change in the full-scale range

output over temperature expressed in parts per million per

degree centigrade (ppm/

°C). Gain drift is established by: (1)

testing the end point differences at t

calculating the gain error with respect to the +25

°C value;

and (3) dividing by the temperature change.

Zero Drift

Zero Drift is a measure of the change in the output with

0000

temperature range. (For the DAC708/709 in unipolar mode,

1

0.1

0.01

0.01

0.1

1

10

Settling Time (µs)

0.001

DAC707

DAC709

R = 100

Ω

R = 1k

Ω

L

L

DAC708