DAC712PLG4 datasheet(14/23 Pages) TI1

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Gain Adjustment

INSTALLATION

GENERAL CONSIDERATIONS

0.01 F

DCOM

ACOM

VOUT

REFOUT

-VCC

0.01 F

+12Vto+15V

-12Vto -15V

POWER-SUPPLY AND REFERENCE

DAC712

SBAS023A – SEPTEMBER 2000 – REVISED JULY 2009 ................................................................................................................................................. www.ti.com

Apply the digital input that gives the maximum

positive voltage output. Adjust the gain potentiometer

or the gain adjust D/A converter for this positive

full-scale voltage.

Because

the

high

accuracy

these

D/A

converters,

system

design

problems

such

grounding

and

contact

resistance

become

very

important. A 16-bit converter with a 20V full-scale

range has a 1LSB value of 305mV. With a load

current

µA, series wiring and connector

resistance of only 60m

Ω causes a voltage drop of

300

µV. To understand what this means in terms of a

system layout, the resistivity of a typical 1-ounce

copper-clad printed circuit board (PCB) is 1/2m

Ω per

square. For a 5mA load, a 10 mil (0.010 inch) wide

printed circuit conductor 60 milli-inches long results in

a voltage drop of 150

µV.

Figure 11. Power-Supply Connections

The analog output of the DAC712 has an LSB size of

305

µV (–96dB). The noise floor of the D/A converter

The DAC712 has separate ANALOG COMMON and

must remain below this level in the frequency range

DIGITAL COMMON pins. The current through DCOM

of interest. The DAC712 noise spectral density (which

is mostly switching transients and are up to 1mA

includes

the

noise

contributed

the

internal

peak in amplitude. The current through ACOM is

reference) is shown in the Typical Characteristics

typically 5

µA for all codes.

section.

Use separate analog and digital ground planes with a

Wiring to high-resolution D/A converters should be

single interconnection point to minimize ground loops.

routed to provide optimum isolation from sources of

The analog pins are located adjacent to each other to

radio

frequency

interference

(RFI)

and

help isolate analog from digital signals. Analog

electromagnetic

interference

(EMI).

The

key

signals should be routed as far as possible from

elimination of RF radiation or pickup is a small loop

digital signals and should cross them at right angles.

area. Signal leads and the return conductors should

solid

analog

ground

plane

around

the

D/A

be kept close together such that they present a small

converter package, as well as under it in the vicinity

capture

cross-section

for

any

external

field.

of the analog and power-supply pins, isolates the D/A

Wire-wrap construction is not recommended.

converter from switching currents. It is recommended

that DCOM and ACOM be connected directly to the

ground planes under the package.

CONNECTIONS

If several DAC712s are used, or if the DAC712

Power-supply decoupling capacitors should be added

shares supplies with other components, connecting

as shown in Figure 11. Best performance occurs

the ACOM and DCOM lines together once at the

using a 1

µF to 10µF tantalum capacitor at –V

CC.

power supplies rather than at each chip may give

Applications with less critical settling time may be

better results.

able to use 0.01

µF at –V

CC as well as at +VCC. The

capacitors should be located close to the package.

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