FEATURES
Complete Dual 12-Bit DAC
No External Components
Single +5 Volt Operation
1 mV/Bit with 4.095 V Full Scale
True Voltage Output, ±5 mA Drive
Very Low Power: 5 mW
APPLICATIONS
Digitally Controlled Calibration
Portable Equipment
Servo Controls
Process Control Equipment
PC Peripherals
GENERAL DESCRIPTION
The AD8582 is a complete, parallel input, dual 12-bit, voltage
output DAC designed to operate from a single +5 volt supply.
Built using a CBCMOS process, this monolithic DAC offers the
user low cost, and ease-of-use in +5 volt only systems.
Included on the chip, in addition to the DACs, are a rail-to-rail
amplifier, latch and reference. The reference (V
to 2.5 volts output, and the on-chip amplifier gains up the DAC
output to 4.095 volts full scale. The user needs only supply a +5
volt supply.
The AD8582 is coded natural binary. The op amp output
swings from 0 volt to +4.095 volts for a one-millivolt-per-bit
resolution, and is capable of driving ± 5 mA. Operation down to
4.3 V is possible with output load currents less than 1 mA.
5.0
∆∆VFS ≤ 1 LSB
4.8
DATA = FFF
TA = +25°C
H
) is trimmed
REF
Complete Dual 12-Bit DAC
AD8582
FUNCTIONAL BLOCK DIAGRAM
The high speed parallel data interface connects to the fastest
processors without wait states. The double-buffered input structure allows the user to load the input registers one at a time,
then a single load strobe tied to both LDA + LDB inputs will
update both DAC outputs simultaneously. LDA and LDB can
also be activated independently to immediately update their respective DAC registers. An address input decodes DAC A or
DAC B when the chip select
nous reset input sets the output to zero scale. The MSB bit can
be used to establish a preset to midscale when the reset input is
strobed.
The AD8582 is available in the 24-pin plastic DIP and the surface mount SOIC-24. Each part is fully specified for operation
over –40°C to +85°C, and the full +5 V ± 5% power supply
range.
CS input is strobed. An asynchro-
REV. 0
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.
4.6
PROPER OPERATION
MIN – Volts
DD
V
4.4
4.2
4.0
0.01
WHEN V
VOLTAGE ABOVE
SUPPLY
DD
CURVE
0.1100101.0
OUTPUT LOAD CURRENT – mA
Figure 1. Minimum Supply Voltage vs. Load
Figure 2. Linearity Error vs. Digital Code and Temperature
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.
Tel: 617/329-4700 Fax: 617/326-8703
AD8582–SPECIFICA TIONS
ELECTRICAL CHARACTERISTICS
(@ VDD = +5.0 V ± 5%, RL = No Load, –40°C ≤ TA ≤ +85°C, unless otherwise noted)
Operating Temperature Range . . . . . . . . . . . . .–40°C to +85°C
Storage Temperature Range . . . . . . . . . . . . .–65°C to +150°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . +300°C
*Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only and functional
operation of the device at these or any other conditions above those indicated in the
operational sections of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
t
CSW
t
t
AS
t
DS
t
LS
AH
t
DH
t
t
S
LDW
± 1LSB
ERROR BAND
t
LH
t
RSW
t
S
A/B
D0–D11
LDA, LDB
RST
V
OUT
CS
Timing Diagram
PIN DESCRIPTION
Pin No. NameDescription
1, 24V
V
OUTA
OUTB
Voltage outputs from the DACs. Fixed
output voltage range of 0 V to 4.095 V
with 1 mV/LSB. An internal
temperature stabilized reference
maintains a fixed full-scale voltage
independent of time, temperature and
power supply variations.
2AGNDAnalog Ground. Ground reference for
the internal bandgap reference voltage,
the DAC, and the output buffer.
3DGND Digital ground for input logic.
4, 21
LDA,Load DAC register strobes. Transfers
LDBinput register data to the DAC registers.
Active low inputs, Level sensitive latch.
May be connected together to double-
buffer load DAC registers.
5MSBDigital Input: High presets DAC
registers to half scale (800
clears DAC registers to zero (000
upon
RST assertion.
6
RSTActive low digital input that clears the
), Low
H
)
H
DAC register to zero, setting the DAC
to minimum scale when MSB pin = 0,
or half-scale when MSB pin = 1.
7–18DB
Twelve Binary Data Bit Inputs. DB11 is
0–11
the MSB and DB0 is the LSB.
19
20
22V
23V
CSChip Select. Active low input.
A/BSelect DAC A = 0 or DAC B = 1.
DD
REF
Positive Supply. Nominal value +5 V, ± 5%.
Nominal 2.5 V reference output
voltage. This node must be buffered if
required to drive external loads.
ModelRangeDescriptionOption
AD8582AN–40°C to +85°C 24-Pin Plastic DIP N-24
AD8582AR–40°C to +85°C 24-Lead SOICSOL-24
AD8582Chips +25°CDie
*For die specifications contact your local Analog Devices sales office. The
AD8582 contains 1270 transistors.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD8582 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
REV. 0
ORDERING INFORMATION*
TemperaturePackagePackage
–3–
PIN CONFIGURATIONS
N-24
24-Pin Plastic DIP
SOL-24
24-Pin SOIC
AD8582
R1
R2
V
OUT
RAIL-TO-RAIL
OUTPUT
AMPLIFIER
R
BANDGAP
REFERENCE
V
REF
2.5V
2R
R
2R
2R
SPDT
N CH FET
SWITCHES
2R
AV = 4.095/2.5
= 1.638V/V
VOLTAGE SWITCHED 12-BIT
R-2R D/A CONVERTER
BUFFER
2R
Table I. Control Logic Truth Table
CSA/BLDALDBRSTMSBInput RegisterDAC Register
LL HHHXWrite to ALatched
LHHHHX Write to BLatched
LLLHHXWrite to AA Transparent
LHHLHXWrite to BB Transparent
HXLLHXLatchedA & B Transparent
HX^^HXLatchedLatched
XXXXLLReset to Zero ScaleReset to Zero Scale
XXXXLHReset to MidscaleReset to Midscale
HXXX^ XLatch Reset ValueLatch Reset Value
^Denotes positive edge triggered.
OPERATION
The AD8582 is a complete, ready-to-use dual 12-bit digital-toanalog converter. Only one +5 V power supply is necessary for
operation. It contains two voltage-switched, 12-bit, lasertrimmed digital-to-analog converters, a curvature-corrected
bandgap reference, rail-to-rail output op amps, input registers,
and DAC registers. The parallel data interface consists of twelve
data bits, DB0–DB11, an address select pin
strobe pins (
tion an asynchronous
zero causing the V
LDA, LDB) and an active low CS strobe. In addi-
RST pin will set all DAC register bits to
to become zero volts, or to midscale for
OUT
trimming applications when the MSB pin is programmed to
Logic 1. This function is useful for power on reset or system
failure recovery to a known state.
A/B, two load
D/A CONVERTER SECTION
The internal DAC is a 12-bit voltage-mode device with an
output that swings from AGND potential to the 2.5 volt internal bandgap voltage. It uses a laser trimmed R-2R
ladder which is switched by N channel MOSFETs. The output voltage of the DAC has a constant resistance independent
of digital input code. The DAC output (not available to the
user) is internally connected to the rail-to-rail output op amp.
AMPLIFIER SECTION
The internal DAC’s output is buffered by a low power consumption precision amplifier. This low power amplifier contains
a differential PNP pair input stage which provides low offset
voltage and low noise, as well as the ability to amplify the zeroscale DAC output voltages. The rail-to-rail amplifier is configured in a gain of 1.6384 (= 4.095 V/2.5 V) in order to set the
4.095 volt full-scale output (1 mV/LSB). See Figure 3 for an
equivalent circuit schematic of the analog section.
The op amp has a 16 µs typical settling time to 0.01%. There
are slight differences in settling time for negative slewing signals
versus positive. See the oscilloscope photos in the Typical Performances section of this data sheet.
Figure 3. Equivalent Schematic of Analog Portion
OUTPUT SECTION
The rail-to-rail output stage of this amplifier has been designed
to provide precision performance while operating near either
power supply. Figure 4 shows an equivalent output schematic of
the rail-to-rail amplifier with its N channel pull-down FETs that
will pull an output load directly to GND. The output sourcing
current is provided by a P channel pull-up device that can supply GND terminated loads, especially important at the –5%
supply tolerance value of 4.75 volts.
V
DD
P-CH
V
N-CH
OUT
AGND
Figure 4. Equivalent Analog Output Circuit
–4–
REV. 0
AD8582
Figures 5 and 6 in the typical performance characteristics section provide information on output swing performance near
ground and full-scale as a function of load. In addition to resistive load driving capability, the amplifier has also been carefully
designed and characterized for up to 500 pF capacitive load
driving capability.
REFERENCE SECTION
The internal 2.5 V curvature-corrected bandgap voltage reference is laser trimmed for both initial accuracy and low temperature coefficient. The voltage generated by the reference is
available at the V
pin. Since V
REF
is not intended to drive ex-
REF
ternal loads, it must be buffered. The equivalent emitter follower output circuit of the V
Bypassing the V
pin will improve noise performance; how-
REF
pin is shown in Figure 3.
REF
ever, bypassing is not required for proper operation. Figure 8
shows broadband noise performance.
POWER SUPPLY
The very low power consumption of the AD8582 is a direct result of a circuit design optimizing use of the CBCMOS process.
By using the low power characteristics of the CMOS for the
logic, and the low noise, tight matching of the complementary
bipolar transistors good analog accuracy is achieved.
For power-consumption sensitive applications it is important to
note that the internal power consumption of the AD8582 is
strongly dependent on the actual logic-input voltage levels
present on the DB0–DB11,
CS, A/B, MSB, LDA, LDB and
RST pins. Since these inputs are standard CMOS logic struc-
tures they contribute static power dissipation dependent on the
actual driving logic V
and VOL voltage levels. The graph in
OH
Figure 9 shows the effect on total AD8582 supply current as a
function of the actual value of input logic voltage. Consequently, for optimum dissipation use of CMOS logic versus
TTL provides minimal dissipation in the static state. A V
INL
=
0 V on the DB0–11 pins provides the lowest standby dissipation
of 1 mA typical with a +5 V power supply.
As with any analog system, it is recommended that the AD8582
power supply be bypassed on the same PC card that contains
the chip. Figure 10 shows the power supply rejection versus frequency performance. This should be taken into account when
using higher frequency switched-mode power supplies with
ripple frequencies of 100 kHz and higher.
One advantage of the rail-to-rail output amplifiers used in the
AD8582 is the wide range of usable supply voltage. The part is
fully specified and tested over temperature for operation from
+4.75 V to +5.25 V. If reduced linearity and source current
capability near full scale can be tolerated, operation of the
AD8582 is possible down to +4.3 volts. The minimum operating supply voltage versus load current plot, in Figure 1, provides information for operation below V
TIMING AND CONTROL
= +4.75 V.
DD
The input registers are level triggered and acquire data from the
data bus during the time period when
ister selected is determined by the
for a complete description. When
latched into the register and held until
CS is low. The input reg-
A/B select pin, see Table I.
CS goes high, the data is
CS returns low. The
minimum time required for the data to be present on the bus
before
CS returns high is called the data setup time (tDS) as seen
in Timing Diagram. The data hold time (t
of time that the data has to remain on the bus after
) is the amount
DH
CS goes
high. The high speed timing offered by the AD8582 provides
for direct interface with no wait states in all but the fastest
microprocessors.
The data from the input registers is transferred to the DAC registers by the active low
LDA and LDB pins. If these inputs are
tied together, a single logic input can perform a double buffer
update of the DAC registers, which in turn simultaneously
changes the analog output voltages to a new value. If the
and
LDB pins are wired low, they become transparent. In this
LDA
mode the input register data will directly control the output
voltages. Refer to the Control Logic Truth
Table for a com-
plete description.
Unipolar Output Operation
This is the basic mode of operation for the AD8582. The
AD8582 has been designed to drive loads as low as 820Ω in parallel with 500 pF. The code table for this operation is shown in
Table II.
Table II. Unipolar Code Table
Hexadecimal
Number in DACDecimal NumberAnalog Output
Registerin DAC RegisterVoltage (V)