AD5602 datasheet(21/24 Pages) AD

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AD5602/AD5612/AD5622

Rev. B | Page 21 of 24

APPLICATIONS

CHOOSING A REFERENCE AS POWER SUPPLY

The AD5602/AD5612/AD5622 come in tiny SC70 packages

with less than 100 μA supply current, thereby making the

choice of reference dependent upon the application

requirement. For space-saving applications, the ADR425 is

available in an SC70 package with excellent drift at 3ppm/°C. It

also provides very good noise performance at 3.4 μV p-p in the

0.1 Hz to 10 Hz range.

Because the supply current required by the AD5602/AD5612/

AD5622 DACs is extremely low, they are ideal for low supply

applications. The ADR293 voltage reference is recommended in

this case. This requires 15 μA of quiescent current and can

therefore drive multiple DACs in the one system, if required.

AD5602/

AD5612/

AD5622

SCL

SDA

VOUT =0V TO 5V

ADR425

Figure 49. ADR425 as Power Supply

Examples of some recommended precision references for use as

supplies to the AD5602/AD5612/AD5622 are shown in Table 8.

Table 8. Recommended Precision References

Part

No.

Initial

Accuracy

(mV max)

Temperature

Drift

(ppm/°C max)

0.1 Hz to 10 Hz Noise

(μV p-p typ)

ADR435

±6

3.4

ADR425

±6

3.4

ADR02

±5

ADR395

±6

BIPOLAR OPERATION

The AD5602/AD5612/AD5622 have been designed for single-

supply operation, but a bipolar output range is also possible

using the circuit in Figure 50. The circuit in Figure 50 gives an

output voltage range of ±5 V. Rail-to-rail operation at the

amplifier output is achievable using an AD820 or an OP295 as

the output amplifier.

The output voltage for any input code can be calculated as

⎥

⎦

⎤

⎢

⎣

⎡

⎟

⎠

⎞

⎜

⎝

⎛

−

⎟

⎠

⎞

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

where:

D represents the input code in decimal.

n represents the bit resolution of the DAC.

With VDD = 5 V, R1 = R2 = 10 kΩ

−

⎟

⎠

⎞

⎜

⎝

⎛

This is an output voltage range of ±5 V with 0x000 corresponding

to a −5 V output, and 0xFFF corresponding to a +5 V output.

+5V

–5V

AD820/

OP295

+5V

AD5602/

AD5612/

AD5622

10µF

0.1µF

VDD

VOUT

10kΩ

SDA SCL

10kΩ

±5V OUT

Figure 50. Bipolar Operation with the AD5602/AD5612/AD5622

POWER SUPPLY BYPASSING AND GROUNDING

When accuracy is important in a circuit, it is helpful to carefully

consider the power supply and ground return layout on the

board. The printed circuit board containing the AD5602/

AD5612/AD5622 should have separate analog and digital

sections, each having its own area of the board. If the AD5602,

AD5612, or AD5622 is in a system where other devices require

an AGND to DGND connection, the connection should be

made at one point only. This ground point should be as close as

possible to the AD5602/AD5612/AD5622.

The power supply to the AD5602/AD5612/AD5622 should be

bypassed with 10 μF and 0.1 μF capacitors. The capacitors

should be physically as close as possible to the device with the

0.1 μF capacitor ideally right up against the device. The 10 μF

capacitors are the tantalum bead type. It is important that the

0.1 μF capacitor has low effective series resistance (ESR) and

effective series inductance (ESI), such as common ceramic

types. This 0.1 μF capacitor provides a low impedance path to

ground for high frequencies caused by transient currents due to

internal logic switching.

The power supply line should have as large a trace as possible to

provide a low impedance path and reduce glitch effects on the

supply line. Clocks and other fast switching digital signals

should be shielded from other parts of the board by digital

ground. Avoid crossover of digital and analog signals if possible.

When traces cross on opposite sides of the board, ensure that

they run at right angles to each other to reduce feedthrough

effects through the board. The best board layout technique is

the microstrip technique where the component side of the

board is dedicated to the ground plane only and the signal

traces are placed on the solder side. However, the microstrip

technique is not always possible with a 2-layer board.

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