AD7242JN(RevB) 데이터 시트보기 (PDF) - Analog Devices

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AD7242JN
(Rev.:RevB)

LC2MOS Dual, Complete, 12-Bit/14-Bit Serial DACs

Analog Devices 

AD7242

APPLYING THE AD7242/AD7244

Low impedance analog and digital power supply common

Good printed circuit board layout is as important as the overall returns are essential to low noise operation of high performance

circuit design itself in achieving high speed converter perfor-

converters. Therefore, the foil width for these tracks should be

mance. The AD7242 works on an LSB size of 1.465 mV, while kept as wide as possible. The use of ground planes minimizes

the AD7244 works on an LSB size of 366 μV. Therefore, the

impedance paths and also guards the analog circuitry from

designer must be conscious of minimizing noise in both the

digital noise.

converter itself and in the surrounding circuitry. Switching

mode power supplies are not recommended as the switching

NOISE

spikes can feed through to the on-chip amplifier. Other causes

of concern are ground loops and digital feedthrough from

Keep the signal leads on the VOUTA and VOUTB signals and the

signal return leads to AGND as short as possible to minimize

microprocessors. These are factors that influence any high

noise coupling. In applications where this is not possible, use a

performance converter, and a proper PCB layout that minimizes shielded cable between the DAC outputs and their destination.

these effects is essential for best performance.

Reduce the ground circuit impedance as much as possible since

LAYOUT HINTS

Ensure that the layout for the printed circuit board has separated

digital and analog lines as much as possible. Take care not to

run any digital track alongside an analog signal track. Establish a

single point analog ground (star ground) separate from the logic

E system ground. Place this star ground as close as possible to the

AD7242/AD7244. Connect all analog grounds to this star

ground and also connect the AD7242/AD7244 DGND pins to

T this ground. Do not connect any other digital grounds to this

OBSOLE analog ground point.

any potential difference in grounds between the DAC and its

destination device appears as an error voltage in series with the

DAC output.

REV. B

–11–

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