AD5439YRUZ datasheet(19/32 Pages) AD

19 / 32 page

AD5429/AD5439/AD5449

Rev. C | Page 19 of 32

REFERENCE SELECTION

When selecting a reference for use with the AD54xx 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 temperature 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 temperature 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 non-

monotonic. 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.

Output Voltage (V)

Initial Tolerance (%)

Temp Drift (ppm/°C)

ISS (mA)

Output Noise (μV p-p)

Package

ADR01

0.05

SOIC-8

ADR01

0.05

TSOT-23, SC70

ADR02

0.06

SOIC-8

ADR02

0.06

TSOT-23, SC70

ADR03

2.5

0.10

SOIC-8

ADR03

2.5

0.10

TSOT-23, SC70

ADR06

0.10

SOIC-8

ADR06

0.10

TSOT-23, SC70

ADR431

2.5

0.04

0.8

3.5

SOIC-8

ADR435

0.04

0.8

SOIC-8

ADR391

2.5

0.16

0.12

TSOT-23

ADR395

0.10

0.12

TSOT-23

Table 8. Suitable Analog Devices Precision Op Amps

Part No.

Supply Voltage (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-8

OP1177

±2.5 to ±15

0.4

500

MSOP, SOIC-8

AD8551

2.7 to 5

0.05

975

MSOP, SOIC-8

AD8603

1.8 to 6

0.001

2.3

TSOT

AD8628

2.7 to 6

0.1

0.5

850

TSOT, SOIC-8

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-8, SOT-23, MSOP

AD8021

±2.5 to ±12

490

120

1000

10,500

SOIC-8, MSOP

AD8038

3 to 12

350

425

3000

750

SOIC-8, SC70-5

AD9631

±3 to ±6

320

1300

10,000

7000

SOIC-8

AD5439YRUZ Datasheet(PDF) 19 Page - Analog Devices

AD5439YRUZ 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 29 30 31 32

Datasheet Download

Link URL