DAC729

6

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 versus code transfer

function from a straight line drawn through the end points

(all bits ON point and all bits OFF point).

Differential Linearity Error

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

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

adjacent output state to the next. A differential linearity error

specification of

±1/2LSB means that the output step sizes

can be between 1/2 LSB and 3/2LSB when the input changes

from one adjacent input state to the next. A negative DLE

specification of no more than –1LSB (–0.0015% for 16-bit

resolution) insures monotonicity to 16 bits.

Monotonicity

Monotonicity assures that the analog output will increase or

remain the same for increasing input digital codes. The

DAC729KH is specified to be monotonic to 16 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 measured by: (1)

testing the end point differences for each D/A at t

and t

+25

°C value; and (3) dividing by the temperature change.

Offset Drift

Offset drift is a measure of the change in the output with

3FFFF

H

applied to the digital inputs over the specified

temperature range. The maximum change in offset at t

t

by the temperature change. This drift is expressed in parts

per million of full-scale range per degree centigrade (ppm of

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. Settling time includes

the slew time of the op amp.

Voltage Output

Settling times are specified to

±0.00076% of FSR scale

range change of 20V (COB) or 10V (CSB) 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

±0.00076% of FSR for a full-

scale range change with an output load resistance of 10

Ω.

COMPLIANCE VOLTAGE

Compliance voltage applies only to the current output mode

of operation. It is the maximum voltage swing allowed on

the output current pin while still being able to maintain

specified linearity.

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 full-

scale output. It is defined as a percent of FSR change in the

output per percent of change in either the positive supply

(+V

the nominal power supply voltages (see Figure 1). It is

specified for DC or low frequency changes. The typical

performance curve in Figure 1 shows the effect of high

frequency changes in power supply voltages using internal

reference, DAC, and op amp.

FIGURE 1. Power Supply Sensitivity vs Frequency Using

Internal Reference and Op Amp.

OPERATING INSTRUCTIONS

POWER SUPPLY CONNECTIONS

For optimum performance and noise rejection, power supply

decoupling capacitors should be added as shown in Figure 2.

These capacitors (1

µF to 10µF tantalum recommended)

should be located at the DAC729.

EXTERNAL OFFSET AND GAIN ADJUSTMENT

Offset and gain may be trimmed by installing external offset

and gain potentiometers. Connect these potentiometers as

shown in Figure 3 and adjust as described below. TCR of

the potentiometers should be 100ppm/

°C or less. The 3.9MΩ

and 510k

Ω resistors (20% carbon or better) should be

located close to the DAC729 to prevent noise pickup. If it

is not convenient to use these high-value resistors, an

equivalent “T” network, as shown in Figure 4, may be

substituted in place of the 3.9M

Ω. A 0.001µF to 0.01µF

capacitor should be connected from Gain Adjust (pin 34) to