AD5667-RBRMZ-2 datasheet(27/30 Pages) AD

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Preliminary Technical Data

AD5627R/AD5647R/AD5667R, AD5627/AD5667

Rev. PrA. | Page 27 of 30

APPLICATIONS

USING A REFERENCE AS A POWER SUPPLY FOR

THE AD5627R/AD5647R/AD5667R,

AD5627/AD5667

Because the supply current required by the

AD5627R/AD5647R/AD5667R, AD5627/AD5667is extremely

low, an alternative option is to use a voltage reference to supply

the required voltage to the part (see Figure). This is especially

useful if the power supply is quite noisy, or if the system supply

voltages are at some value other than 5 V or 3 V, for example,

15 V. The voltage reference outputs a steady supply voltage for

the AD5627R/AD5647R/AD5667R, AD5627/AD5667. If the low

dropout REF195 is used, it must supply 450 µA of current to the

AD5627R/AD5647R/AD5667R, AD5627/AD5667 with no load

on the output of the DAC. When the DAC output is loaded, the

REF195 also needs to supply the current to the load. The total

current required (with a 5 kΩ load on the DAC output) is

450 µA + (5 V/5 kΩ) = 1.45 mA

The load regulation of the REF195 is typically 2 ppm/mA,

resulting in a 2.9 ppm (14.5 µV) error for the 1.45 mA current

drawn from it. This corresponds to a 0.191 LSB error.

REF195

2-WIRE

SERIAL

INTERFACE

SCL

SDA

VDD

AD5627(R)/

AD5647R/

AD5667(R)

VOUT =0V TO 5V

GND

15V

Figure 65. REF195 as Power Supply to the AD5627R/AD5647R/AD5667R,

AD5627/AD5667

BIPOLAR OPERATION USING THE

AD5627R/AD5647R/AD5667R, AD5627/AD5667

The AD5627R/AD5647R/AD5667R, AD5627/AD5667 has been

designed for single-supply operation, but a bipolar output range

is also possible using the circuit in Figure 67. The circuit 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

follows:

⎥

⎦

⎤

⎢

⎣

⎡

⎟

⎠

⎞

⎜

⎝

⎛

−

⎟

⎠

⎞

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

536

where D represents the input code in decimal (0 to 65535).

With VDD = 5 V, R1 = R2 = 10 kΩ,

536

−

⎟

⎠

⎞

⎜

⎝

⎛

This is an output voltage range of ±5 V, with 0x0000 corre-

sponding to a −5 V output, and 0xFFFF corresponding to a

+5 V output.

2-WIRE

SERIAL

INTERFACE

SCL SDA

VDD

GND

+5V

10µF

0.1µF

AD5627(R)/

AD5647R/

AD5667(R)

VOUT

R1 = 10k

Ω

R2 = 10k

Ω

+5V

-5V

AD820/

OP295

±5V

Figure 66. Bipolar Operation with the AD5627R/AD5647R/AD5667R,

AD5627/AD5667

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

AD5627R/AD5647R/AD5667R, AD5627/AD5667 should have

separate analog and digital sections, each having its own area of

the board. If the AD5627R/AD5647R/AD5667R,

AD5627/AD5667 are 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 AD5627R/AD5647R/AD5667R, AD5627/AD5667.

The power supply to the AD5627R/AD5647R/AD5667R,

AD5627/AD5667 should be bypassed with 10 µF and 0.1 µF

capacitors. The capacitors should be located as close as possible

to the device, with the 0.1 µF capacitor ideally right up against

the device. The 10 µF capacitor is the tantalum bead type. It is

important that the 0.1 µF capacitor have low effective series

resistance (ESR) and effective series inductance (ESI), for

example, common ceramic types of capacitors. 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 itself should have as large a trace as

possible to provide a low impedance path and to 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, this is not

always possible with a 2-layer board.

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