AD5429 datasheet(19/28 Pages) AD

19 / 28 page

Data Sheet

AD5429/AD5439/AD5449

Rev. F | Page 19 of 28

REFERENCE SELECTION

When selecting a reference for use with the AD5429/AD5439/

AD5449 series of current output DACs, pay attention to the

reference output voltage temperature coefficient specification. This

parameter affects not only the full-scale error, but it can also affect

the linearity (INL and DNL) performance. The reference tempera-

ture coefficient should be consistent with the system accuracy

specifications. For example, an 8-bit system required to hold its

overall specification to within 1 LSB over the temperature range of

0°C to 50°C dictates that the maximum system drift with tempera-

ture should be less than 78 ppm/°C. A 12-bit system with the same

temperature range to overall specification within 2 LSBs requires a

maximum drift of 10 ppm/°C. By choosing a precision reference

with a low output temperature coefficient, this error source can be

minimized. Table 7 lists some references available from Analog

Devices, Inc., that are suitable for use with this range of current

output DACs.

AMPLIFIER SELECTION

The primary requirement for the current-steering mode is an

amplifier with low input bias currents and low input offset voltage.

Because of the code-dependent output resistance of the DAC, the

input offset voltage of an op amp is multiplied by the variable gain

of the circuit. A change in this noise gain between two adjacent

digital fractions produces a step change in the output voltage due to

the amplifier input offset voltage. This output voltage change is

superimposed on the desired change in output between the two

codes and gives rise to a differential linearity error, which, if

large enough, could cause the DAC to be nonmonotonic. The

input bias current of an op amp also generates an offset at the

voltage output as a result of the bias current flowing in the feedback

resistor, RFB. Most op amps have input bias currents low enough

to prevent significant errors in 12-bit applications.

Common-mode rejection of the op amp is important in voltage-

switching circuits because it produces a code-dependent error

at the voltage output of the circuit. Most op amps have adequate

common-mode rejection for use at 8-, 10-, and 12-bit resolution.

If the DAC switches are driven from true wideband low impedance

sources (VIN and AGND), they settle quickly. Consequently, the

slew rate and settling time of a voltage-switching DAC circuit

is determined largely by the output op amp. To obtain minimum

settling time in this configuration, minimize capacitance at the VREF

node (the voltage output node in this application) of the DAC by

using low input capacitance buffer amplifiers and careful board

design.

Most single-supply circuits include ground as part of the analog

signal range, which, in turn, requires an amplifier that can handle

rail-to-rail signals. Analog Devices offers a wide range of single-

supply amplifiers (see Table 8 and Table 9).

Table 7. Suitable Analog Devices Precision References

Part No.

OutputVoltage (V)

Initial Tolerance (%)

Temp Drift (ppm/°C)

ISS (mA)

Output Noise (µV p-p)

Package

ADR01

0.05

SOIC

ADR01

0.05

TSOT, SC70

ADR02

0.06

SOIC

ADR02

0.06

TSOT, SC70

ADR03

2.5

0.10

SOIC

ADR03

2.5

0.10

TSOT, SC70

ADR06

0.10

SOIC

ADR06

0.10

TSOT, SC70

ADR431

2.5

0.04

0.8

3.5

SOIC

ADR435

0.04

0.8

SOIC

ADR391

2.5

0.16

0.12

TSOT

ADR395

0.10

0.12

TSOT

Table 8. Suitable Analog Devices Precision Op Amps

Part No.

SupplyVoltage (V)

VOS (Max) (µV)

IB (Max) (nA)

0.1 Hz to 10 Hz Noise (µV p-p)

Supply Current (µA)

Package

OP97

±2 to ±20

0.1

0.5

600

SOIC

OP1177

±2.5 to ±15

0.4

500

MSOP, SOIC

AD8551

2.7 to 5

0.05

975

MSOP, SOIC

AD8603

1.8 to 6

0.001

2.3

TSOT

AD8628

2.7 to 6

0.1

0.5

850

TSOT, SOIC

Table 9. Suitable Analog Devices High Speed Op Amps

Part No.

Supply Voltage (V)

BW @ ACL (MHz)

Slew Rate (V/µs)

VOS (Max) (µV)

IB (Max) (nA)

Package

AD8065

5 to 24

145

180

1500

6000

SOIC, SOT-23, MSOP

AD8021

±2.5 to ±12

490

120

1000

10,500

SOIC, MSOP

AD8038

3 to 12

350

425

3000

750

SOIC, SC70

AD9631

±3 to ±6

320

1300

10,000

7000

SOIC

AD5429 Datasheet(PDF) 19 Page - Analog Devices

AD5429 Datasheet(HTML) 19 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Datasheet Download

Link URL