AD7228ABQ AD [Analog Devices], AD7228ABQ Datasheet - Page 5

• Manufacturer Part Number: AD7228ABQ
• Description: LC2MOS Octal 8-Bit DAC
• Manufacturer: AD [Analog Devices]

REV. A
OP AMP SECTION
Each voltage-mode D/A converter output is buffered by a unity
gain noninverting CMOS amplifier. This buffer amplifier is
tested with a 2 k and 100 pF load but will typically drive a
2 k and 500 pF load.
The AD7228A can be operated single or dual supply. Operating
the part from single or dual supplies has no effect on the positive-
going settling time. However, the negative-going settling time to
voltages near 0 V in single supply will be slightly longer than the
settling time for dual supply operation. Additionally, to ensure
that the output voltage can go to 0 V in single supply, a transis-
tor on the output acts as a passive pull-down as the output volt-
age nears 0 V. As a result, the sink capability of the amplifier is
reduced as the output voltage nears 0 V in single supply. In dual
supply operation, the full sink capability of 400 A at 25 C is
maintained over the entire output voltage range. The single sup-
ply output sink capability is shown in Figure 4. The negative
V
an extended input reference voltage range and giving improved
slew rate at the output.
The output broadband noise from the amplifier is 300 V
peak-to-peak. Figure 5 shows a plot of noise spectral density
versus frequency.
DIGITAL INPUTS
The AD7228A digital inputs are compatible with either TTL or
5 V CMOS levels. All logic inputs are static-protected MOS
gates with typical input currents of less than 1 nA. Internal in-
put protection is achieved by on-chip distributed diodes.
SS
also gives improved output amplifier performance allowing
Figure 5. Noise Spectral Density vs. Frequency
Figure 4. Single Supply Sink Current
–5–
SUPPLY CURRENT
The AD7228A has a maximum I
a maximum I
ture range. This maximum current specification is actually de-
termined by the current at –55 C. Figure 6 shows a typical plot
of power supply current versus temperature.
APPLYING THIS AD7228A
UNIPOLAR OUTPUT OPERATION
This is the basic mode of operation for each channel of the
AD7228A, with the output voltage having the same positive po-
larity as V
shown in Figure 7. The AD7228A can be operated from single
or dual supplies as outlined earlier. The voltage at the reference
input must never be negative with respect to GND. Failure to
observe this precaution may cause parasitic transistor action and
possible device destruction. The code table for unipolar output
operation is shown in Table II.
Figure 6. Power Supply Current vs. Temperature
REF
. Connections for unipolar output operation are
SS
Figure 7. Unipolar Output Circuit
of 20 mA over the –55 C to +125 C tempera-
DD
specification of 22 mA and
AD7228A