AD8803AN 데이터 시트보기 (PDF) - Analog Devices

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AD8803AN

Octal 8-Bit TrimDAC with Power Shutdown

Analog Devices 

AD8801/AD8803

0.04

x + 2σ

0.02

x

0

–0.02

x – 2σ

VDD = +4.5V

VREF = +4.5V

SS = 162 PCS

–0.04

0

150

300

450

600

HOURS OF OPERATION AT 150°C

Figure 19. Full-Scale Error Accelerated by Burn-In

1.0

0.5

x + 2σ

x

0

x – 2σ

–0.5

VDD = +4.5V

VREF = +4.5V

CODE = 55H

SS = 162 PCS

–1.0

0

150

300

450

600

HOURS OF OPERATION AT 150°C

Figure 20. REF Input Resistance Accelerated by Burn-In

APPLICATIONS

Supply Bypassing

Precision analog products, such as the AD8801/AD8803, re-

quire a well filtered power source. Since the AD8801/AD8803

operate from a single +3 V to +5 V supply, it seems convenient

to simply tap into the digital logic power supply. Unfortunately,

the logic supply is often a switch-mode design, which generates

noise in the 20 kHz to 1 MHz range. In addition, fast logic gates

can generate glitches hundred of millivolts in amplitude due to

wiring resistances and inductances.

If possible, the AD8801/AD8803 should be powered directly

from the system power supply. This arrangement, shown in Fig-

ure 21, will isolate the analog section from the logic switching

transients. Even if a separate power supply trace is not available,

however, generous supply bypassing will reduce supply-line in-

duced errors. Local supply bypassing consisting of a 10 µF tan-

talum electrolytic in parallel with a 0.1 µF ceramic capacitor is

recommended (Figure 22).

TTL/CMOS

LOGIC

CIRCUITS

+ 10µF

TANT

0.1µF

AD8801/

AD8803

+5V

POWER SUPPLY

Figure 21. Use Separate Traces to Reduce Power Supply

Noise

+5V

+

10µF

0.1µF

VDD

AD8801/

AD8803

DGND

Figure 22. Recommended Supply Bypassing for the

AD8801/AD8803

Buffering the AD8801/AD8803 Output

In many cases, the nominal 5 kΩ output impedance of the

AD8801/AD8803 is sufficient to drive succeeding circuitry. If a

lower output impedance is required, an external amplifier can

be added. Several examples are shown in Figure 23. One ampli-

fier of an OP291 is used as a simple buffer to reduce the output

resistance of DAC A. The OP291 was chosen primarily for its

rail-to-rail input and output operation, but it also offers opera-

tion to less than 3 V, low offset voltage, and low supply current.

The next two DACs, B and C, are configured in a summing ar-

rangement where DAC C provides the coarse output voltage

setting and DAC B can be used for fine adjustment. The inser-

tion of R1 in series with DAC B attenuates its contribution to

the voltage sum node at the DAC C output.

–8–

REV. A

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