a
FEATURES
Complete 14-Bit Voltage Output DAC
Parallel and Serial Interface Capability
80 dB Signal-to-Noise Ratio
Interfaces to High Speed DSP Processors
e.g., ADSP-2100, TMS32010, TMS32020
45 ns min
WR
Pulse Width
Low Power – 70 mW typ.
Operates from 5 V Supplies
LC MOS
Complete 14-Bit DAC
AD7840
FUNCTIONAL BLOCK DIAGRAM
2
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD7840 is a fast, complete 14-bit voltage output D/A con-
verter. It consists of a 14-bit DAC, 3 V buried Zener reference,
DAC output amplifier and high speed control logic.
The part features double-buffered interface logic with a 14-bit
input latch and 14-bit DAC latch. Data is loaded to the input
latch in either of two modes, parallel or serial. This data is then
transferred to the DAC latch under control of an asynchronous
LDAC
signal. A fast data setup time of 21 ns allows direct
parallel interfacing to digital signal processors and high speed
16-bit microprocessors. In the serial mode, the maximum serial
data clock rate can be as high as 6 MHz.
The analog output from the AD7840 provides a bipolar output
range of
±
3 V. The AD7840 is fully specified for dynamic per-
formance parameters such as signal-to-noise ratio and harmonic
distortion as well as for traditional dc specifications. Full power
output signals up to 20 kHz can be created.
The AD7840 is fabricated in linear compatible CMOS
(LC
2
MOS), an advanced, mixed technology process that com-
bines precision bipolar circuits with low power CMOS logic.
The part is available in a 24-pin plastic and hermetic
dual-in-line package (DIP) and is also packaged in a 28-termi-
nal plastic leaded chip carrier (PLCC).
1. Complete 14-Bit D/A Function
The AD7840 provides the complete function for creating ac
signals and dc voltages to 14-bit accuracy. The part features
an on-chip reference, an output buffer amplifier and 14-bit
D/A converter.
2. Dynamic Specifications for DSP Users
In addition to traditional dc specifications, the AD7840 is
specified for ac parameters including signal-to-noise ratio and
harmonic distortion. These parameters along with important
timing parameters are tested on every device.
3. Fast, Versatile Microprocessor Interface
The AD7840 is capable of 14-bit parallel and serial interfac-
ing. In the parallel mode, data setup times of 21 ns and write
pulse widths of 45 ns make the AD7840 compatible with
modern 16-bit microprocessors and digital signal processors.
In the serial mode, the part features a high data transfer rate
of 6 MHz.
REV. B
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
AD7840–SPECIFICATIONS
Parameter
DYNAMIC PERFORMANCE
2
Signal to Noise Ratio
3
(SNR)
J, A
1
76
K, B
1
78
–80
–80
Total Harmonic Distortion (THD) –78
Peak Harmonic or Spurious Noise
DC ACCURACY
Resolution
Integral Nonlinearity
Differential Nonlinearity
Bipolar Zero Error
Positive Full Scale Error
5
Negative Full Scale Error
5
REFERENCE OUTPUT
6
REF OUT @ +25°C
REF OUT TC
Reference Load Change
(∆REF OUT vs.
∆I)
REFERENCE INPUT
Reference Input Range
Input Current
LOGIC INPUTS
Input High Voltage, V
INH
Input Low Voltage, V
INL
Input Current, I
IN
Input Current (CS Input Only)
Input Capacitance, C
IN7
ANALOG OUTPUT
Output Voltage Range
DC Output Impedance
Short-Circuit Current
AC CHARACTERISTICS
7
Voltage Output Settling Time
Positive Full-Scale Change
Negative Full-Scale Change
Digital-to-Analog Glitch Impulse
Digital Feedthrough
POWER REQUIREMENTS
V
DD
V
SS
I
DD
I
SS
Power Dissipation
–78
(V
DD
= +5 V 5%, V
SS
= –5 V 5%, AGND = DGND = O V, REF IN = +3 V, R
L
= 2 k ,
C
L
= 100 pF. All specifications T
MIN
to T
MAX
unless othewise noted.)
S
1
76
–78
–78
Units
dB min
dB max
dB max
Test Conditions/Comments
V
OUT
= 1 kHz Sine Wave, f
SAMPLE
= 100 kHz
Typically 82 dB at +25°C for 0 < V
OUT
< 20 kHz
4
V
OUT
= 1 kHz Sine Wave, f
SAMPLE
= 100 kHz
Typically –84 dB at +25°C for 0 < V
OUT
< 20 kHz
4
V
OUT
= 1 kHz Sine Wave, f
SAMPLE
= 100 kHz
Typically –84 dB at +25°C for 0 < V
OUT
< 20 kHz
4
14
±
2
±
0.9
±
10
±
10
±
10
2.99
3.01
±
60
–1
2.85
3.15
50
2.4
0.8
±
10
±
10
10
±
3
0.1
20
14
±
1
±
0.9
±
10
±
10
±
10
2.99
3.01
±
60
–1
2.85
3.15
50
2.4
0.8
±
10
±
10
10
±
3
0.1
20
14
±
2
±
0.9
±
10
±
10
±
10
2.99
3.01
±
60
–1
2.85
3.15
50
2.4
0.8
±
10
±
10
10
±
3
0.1
20
Bits
LSB max
LSB max
LSB max
LSB max
LSB max
V min
V max
ppm/°C max
mV max
V min
V max
µA
max
V min
V max
µA
max
µA
max
pF max
V nom
Ω
typ
mA typ
Guaranteed Monotonic
Reference Load Current Change (0–500
µA)
3 V
±
5%
V
DD
= 5 V
±
5%
V
DD
= 5 V
±
5%
V
IN
= 0 V to V
DD
V
IN
=V
SS
to V
DD
4
4
10
2
+5
–5
14
6
100
4
4
10
2
+5
–5
14
6
100
4
4
10
2
+5
–5
15
7
110
µs
max
µs
max
nV secs typ
nV secs typ
V nom
V nom
mA max
mA max
mW max
Settling Time to within
±
1/2 LSB of Final Value
Typically 2
µs
Typically 2.5
µs
±
5% for Specified Performance
±
5% for Specified Performance
Output Unloaded, SCLK = +5 V. Typically 10 mA
Output Unloaded, SCLK = +5 V. Typically 4 mA
Typically 70 mW
NOTES
1
Temperature ranges are as follows: J, K Versions, 0°C to +70°C; A, B Versions, –25°C to +85°C; S Version, –55°C to +125°C.
2
V
OUT
(pk-pk) =
±
3 V
3
SNR calculation includes distortion and noise components.
4
Using external sample-and-hold (see Testing the AD7840).
5
Measured with respect to REF IN and includes bipolar offset error.
6
For capacitive loads greater than 50 pF, a series resistor is required (see Internal Reference section).
7
Sample tested @ +25°C to ensure compliance.
Specifications subject to change without notice.
–2–
REV. B
AD7840
TIMING CHARACTERISTICS
1, 2
Parameter
t
1
t
2
t
3
t
4
t
5
t
6
t
7
t
8 3
t
9
t
10
t
11
Limit at T
MIN
, T
MAX
(J, K, A, B Versions)
0
0
45
21
10
40
50
150
30
75
75
(V
DD
= +5 V
5%, V
SS
= –5 V
5%, AGND = DGND = 0 V.)
Units
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
Conditions/Comments
CS
to
WR
Setup Time
CS
to
WR
Hold Time
WR
Pulse Width
Data Valid to
WR
Setup Time
Data Valid to
WR
Hold Time
LDAC
Pulse Width
SYNC
to SCLK Falling Edge
SCLK Cycle Time
Data Valid to SCLK Setup Time
Data Valid to SCLK Hold Time
SYNC
to SCLK Hold Time
Limit at T
MIN
, T
MAX
(S Version)
0
0
50
28
15
40
50
200
40
100
100
NOTES
1
Timing specifications in
bold print
are 100% production tested. All other times are sample tested at +25
°C
to ensure compliance. All input signals are specified with
tr = tf = 5 ns (10% to 90% of 5 V) and timed from a voltage level of 1.6 V.
2
See Figures 6 and 8.
3
SCLK mark/space ratio is 40/60 to 60/40.
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*
ORDERING GUIDE
Temperature
Range
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
–25°C to +85°C
–25°C to +85°C
–25°C to +85°C
–55°C to +125°C
SNR
(dB)
78 min
80 min
78 min
80 min
78 min
78 min
80 min
78 min
Integral
Nonlinearity
(LSB)
±
2 max
±
1 max
±
2 max
±
1 max
±
2 max
±
2 max
±
1 max
±
2 max
Package
Option
2
N-24
N-24
P-28A
P-28A
Q-24
RS-24
Q-24
Q-2
4
V
DD
to AGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V
V
SS
to AGND . . . . . . . . . . . . . . . . . . . . . . . . . +0.3 V to –7 V
AGND to DGND . . . . . . . . . . . . . . . . –0.3 V to V
DD
+ 0.3 V
V
OUT
to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . V
SS
to V
DD
REF OUT to AGND . . . . . . . . . . . . . . . . . . . . . . . 0 V to V
DD
REF IN to AGND . . . . . . . . . . . . . . . . –0.3 V to V
DD
+ 0.3 V
Digital Inputs to DGND . . . . . . . . . . . –0.3 V to V
DD
+ 0.3 V
Operating Temperature Range
Commercial (J, K Versions) . . . . . . . . . . . . . . 0°C to +70°C
Industrial (A, B Versions) . . . . . . . . . . . . . . –25°C to +85°C
Extended (S Version) . . . . . . . . . . . . . . . . –55°C to +125°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . +300°C
Power Dissipation (Any Package) to +75°C . . . . . . . . 450 mW
Derates above +75°C by . . . . . . . . . . . . . . . . . . . . 10 mW/°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 listed in the
operational sections of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
Model
1
AD7840JN
AD7840KN
AD7840JP
AD7840KP
AD7840AQ
AD7840ARS
AD7840BQ
AD7840SQ
3
NOTES
1
To order MIL-STD-883, Class B processed parts, add /883B to part number.
Contact your local sales office for military data sheet and availability.
2
N = Plastic DIP; P = Plastic Leaded Chip Carrier; Q = Cerdip.
3
This grade will be available to /883B processing only.
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 AD7840 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.
WARNING!
ESD SENSITIVE DEVICE
REV. B
–3–
AD7840
PIN FUNCTION DESCRIPTION
DIP
Pin
No.
1
Pin
Mnemonic
CS/SERIAL
Function
Chip Select/Serial Input. When driven with normal logic levels, it is an active low logic input which is used
in conjunction with
WR
to load parallel data to the input latch. For applications where
CS
is perma-
nently low, an R, C is required for correct power-up (see
LDAC
input). If this input is tied to V
SS
, it de-
fines the AD7840 for serial mode operation.
Write/Frame Synchronization Input. In the parallel data mode, it is used in conjunction with
CS
to load
parallel data. In the serial mode of operation, this pin functions as a Frame Synchronization pulse with se-
rial data expected after the falling edge of this signal.
Data Bit 13(MSB)/Serial Data. When parallel data is selected, this pin is the D13 input. In serial mode,
SDATA is the serial data input which is used in conjunction with
SYNC
and SCLK to transfer serial data
to the AD7840 input latch.
Data Bit 12/Serial Clock. When parallel data is selected, this pin is the D12 input. In the serial mode, it is
the serial clock input. Serial data bits are latched on the falling edge of SCLK when
SYNC
is low.
Data Bit 11/Data Format. When parallel data is selected, this pin is the D11 input. In serial mode, a Logic
1 on this input indicates that the MSB is the first valid bit in the serial data stream. A Logic 0 indicates
that the LSB is the first valid bit (see Table I).
Data Bit 10/Data Justification. When parallel data is selected, this pin is the D10 input. In serial mode,
this input controls the serial data justification (see Table I).
Data Bit 9 to Data Bit 5. Parallel data inputs.
Digital Ground. Ground reference for digital circuitry.
Data Bit 4 to Data Bit 1. Parallel data inputs.
Data Bit 0 (LSB). Parallel data input.
Positive Supply, +5 V
±
5%.
Analog Ground. Ground reference for DAC, reference and output buffer amplifier.
Analog Output Voltage. This is the buffer amplifier output voltage. Bipolar output range (± 3 V with REF
IN = +3 V).
Negative Supply Voltage, –5 V
±
5%.
Voltage Reference Output. The internal 3 V analog reference is provided at this pin. To operate the
AD7840 with internal reference, REF OUT should be connected to REF IN. The external load capability
of the reference is 500
µA.
Voltage Reference Input. The reference voltage for the DAC is applied to this pin. It is internally buffered
before being applied to the DAC. The nominal reference voltage for correct operation of the AD7840 is
3 V.
Load DAC. Logic Input. A new word is loaded into the DAC latch from the input latch on the falling
edge of this signal (see Interface Logic Information section). The AD7840 should be powered-up with
LDAC
high. For applications where
LDAC
is permanently low, an R, C is required for correct power-up
(see Figure 19).
Table I. Serial Data Modes
2
WR/SYNC
3
D13/SDATA
4
5
D12/SCLK
D11/FORMAT
6
7–11
12
13–16
17
18
19
20
21
22
D10/JUSTIFY
D9–D5
DGND
D4–D1
D0
V
DD
AGND
V
OUT
V
SS
REF OUT
23
REF IN
24
LDAC
–4–
REV. B
AD7840
PIN CONFIGURATIONS
DIP/SSOP
PLCC
D/A SECTION
The AD7840 contains a 14-bit voltage mode D/A converter
consisting of highly stable thin film resistors and high speed
NMOS single-pole, double-throw switches. The simplified cir-
cuit diagram for the DAC section is shown in Figure 1. The
three MSBs of the data word are decoded to drive the seven
switches A–G. The 11 LSBs switch an 11-bit R-2R ladder struc-
ture. The output voltage from this converter has the same polar-
ity as the reference voltage, REF IN.
The REF IN voltage is internally buffered by a unity gain ampli-
fier before being applied to the D/A converter and the bipolar
bias circuitry. The D/A converter is configured and sealed for a
3 V reference and the device is tested with 3 V applied to REF
IN. Operating the AD7840 at reference voltages outside the
±
5% tolerance range may result in degraded performance from
the part.
for external use, it should he decoupled to AGND with a 200
Ω
resistor in series with a parallel combination of a 10
µF
tantalum
capacitor and a 0.1
µF
ceramic capacitor.
Figure 2. Internal Reference
EXTERNAL REFERENCE
In some applications, the user may require a system reference or
some other external reference to drive the AD7840 reference in-
put. Figure 3 shows how the AD586 5 V reference can be con-
ditioned to provide the 3 V reference required by the AD7840
REF IN. An alternate source of reference voltage for the
AD7840 in systems which use both a DAC and an ADC is to
use the REF OUT voltage of ADCs such as the AD7870 and
AD7871. A circuit showing this arrangement is shown in
Figure 20.
Figure 1. DAC Ladder Structure
INTERNAL REFERENCE
The AD7840 has an on-chip temperature compensated buried
Zener reference (see Figure 2) which is factory trimmed to 3 V
±
10 mV. The reference voltage is provided at the REF OUT
pin. This reference can be used to provide both the reference
voltage for the D/A converter and the bipolar bias circuitry. This
is achieved by connecting the REF OUT pin to the REF IN pin
of the device.
The reference voltage can also be used as a reference for other
components and is capable of providing up to 500
µA
to an ex-
ternal load. The maximum recommended capacitance on REF
OUT for normal operation is 50 pF. If the reference is required
REV. B
–5–
Figure 3. AD586 Driving AD7840 REF IN
京公网安备 11010802033920号
EEWORLD
