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PDF AD7228A Data sheet ( Hoja de datos )
| Número de pieza | AD7228A | |
| Descripción | LC2MOS Octal 8-Bit DAC | |
| Fabricantes | Analog Devices | |
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FEATURES
Eight 8-Bit DACs with Output Amplifiers
Operates with Single +5 V, +12 V or +15 V
or Dual Supplies
P Compatible (95 ns WR Pulse)
No User Trims Required
Skinny 24-Pin DlPs, SOIC, and 28-Terminal Surface
Mount Packages
LC2MOS
Octal 8-Bit DAC
AD7228A
FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The AD7228A contains eight 8-bit voltage-mode digital-to-
analog converters, with output buffer amplifiers and interface
logic on a single monolithic chip. No external trims are required
to achieve full specified performance for the part.
Separate on-chip latches are provided for each of the eight D/A
converters. Data is transferred into the data latches through a
common 8-bit TTL/CMOS (5 V) compatible input port. Ad-
dress inputs A0, A1 and A2 determine which latch is loaded
when WR goes low. The control logic is speed compatible with
most 8-bit microprocessors.
Specified performance is guaranteed for input reference voltages
from +2 to +10 V when using dual supplies. The part is also
specified for single supply +15 V operation using a reference of
+10 V and single supply +5 V operation using a reference of
+1.23 V. Each output buffer amplifier is capable of developing
+10 V across a 2 kΩ load.
The AD7228A is fabricated on an all ion-implanted, high-
speed, Linear Compatible CMOS (LC2MOS) process which has
been specifically developed to integrate high-speed digital logic
circuits and precision analog circuits on the same chip.
PRODUCT HIGHLIGHTS
1. Eight DACs and Amplifiers in Small Package
The single-chip design of eight 8-bit DACs and amplifiers al-
lows a dramatic reduction in board space requirements and
offers increased reliability in systems using multiple convert-
ers. Its pinout is aimed at optimizing board layout with all
analog inputs and outputs at one side of the package and all
digital inputs at the other.
2. Single or Dual Supply Operation
The voltage-mode configuration of the DACs allows single
supply operation of the AD7228A. The part can also be oper-
ated with dual supplies giving enhanced performance for
some parameters.
3. Microprocessor Compatibility
The AD7228A has a common 8-bit data bus with individual
DAC latches, providing a versatile control architecture for
simple interface to microprocessors. All latch enable signals
are level triggered and speed compatible with most high per-
formance 8-bit microprocessors.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
1 page  
AD7228A
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 kΩ and 100 pF load but will typically drive a
2 kΩ 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 µA 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
VSS also gives improved output amplifier performance allowing
an extended input reference voltage range and giving improved
slew rate at the output.
SUPPLY CURRENT
The AD7228A has a maximum IDD specification of 22 mA and
a maximum ISS of 20 mA over the –55°C to +125°C tempera-
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.
Figure 4. Single Supply Sink Current
The output broadband noise from the amplifier is 300 µV
peak-to-peak. Figure 5 shows a plot of noise spectral density
versus frequency.
Figure 6. Power Supply Current vs. 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 VREF. Connections for unipolar output operation are
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 5. Noise Spectral Density vs. 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.
REV. A
–5–
Figure 7. Unipolar Output Circuit
5 Page | ||
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| PDF Descargar | [ Datasheet AD7228A.PDF ] | |
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