LC2MOS
a
FEATURES
Two 12-Bit DACs in One Package
DAC Ladder Resistance Matching: 0.5%
Surface-Mount Package
4-Quadrant Multiplication
Low Gain Error (3 LSB max Over Temperature)
Byte Loading Structure
Fast Interface Timing
APPLICATIONS
Automatic Test Equipment
Programmable Filters
Audio Applications
Synchro Applications
Process Control
GENERAL DESCRIPTION
The AD7937 contains two 12-bit current output DACs on one
monolithic chip. A separate reference input is provided for each
DAC. The dual DAC saves valuable board space, and the monolithic construction ensures excellent thermal tracking. Both DACs
are guaranteed 12-bit monotonic over the full temperature range.
The AD7937 has a 2-byte (eight LSBs, four MSBs) loading
structure. It is designed for right-justified data format. The control
signals for register loading are A0, A1, CS, WR, and UPD. Data
is loaded to the input registers when CS and WR are low. To
transfer this data to the DAC registers, UPD must be taken
low with WR.
Added features on the AD7937 include an asynchronous CLR
line which is very useful in calibration routines. When this is
taken low, all registers are cleared. The double buffering of the
data inputs allows simultaneous update of both DACs. Also,
each DAC has a separate AGND line. This increases the device
versatility; for instance, one DAC may be operated with AGND
biased while the other is connected in the standard configuration.
The AD7937 is manufactured using the Linear Compatible
CMOS (LC
microprocessors and accepts TTL, 74HC, and 5 V CMOS logic
level inputs.
2
MOS) process. It is speed compatible with most
(8+4) Loading Dual 12-Bit DAC
AD7937
FUNCTIONAL BLOCK DIAGRAM
V
DD
AD7937
UPD
A1
A0
CONTROL
CS
WR
CLR
LOGIC
DB7–DB0 DGND
PRODUCT HIGHLIGHTS
1. DAC-to-DAC Matching
Since both DACs are fabricated on the same chip, precise
matching and tracking is inherent. Many applications that are
not practical using two discrete DACs are now possible.
Typical matching: 0.5%.
2. Small Package Size
The AD7937 is packaged in a small 24-lead SOIC.
3. Wide Power Supply Tolerance
The device operates on a 5 V V
this nominal figure. All specifications are guaranteed over
this range.
DAC A MS
INPUT REG
48
DAC A REGISTER
DAC B REGISTER
48
DAC B MS
INPUT REG
DD
DAC A LS
INPUT REG
12
DAC A
DAC B
12
DAC B LS
INPUT REG
, with ±10% tolerance on
I
OUTA
AGNDA
R
FBA
V
REFA
V
REFB
R
FBB
I
OUTB
AGNDB
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2000
AD7937–SPECIFICATIONS
(VDD = 5 V 10%, V
specifications T
MIN
= V
REFA
to T
MAX
= 10 V; I
REFB
unless otherwise noted.)
= AGNDA = 0 V, I
OUTA
= AGNDB = 0 V. All
OUTB
Parameter A Version B Version Unit Test Conditions/Comments
ACCURACY
Resolution 12 12 Bits
Relative Accuracy ±1 ±1/2 LSB max
Differential Nonlinearity ±1 ±1 LSB max All grades guaranteed monotonic over temperature.
, R
Gain Error ±6 ±3 LSB max Measured using R
Gain Temperature Coefficient
2
;
. Both DAC registers loaded with all 1s.
FBA
FBB
∆Gain/∆Temperature ±5 ±5 ppm/°C max Typical value is 1 ppm/°C.
Output Leakage Current
I
OUTA
I
OUTB
5 5 nA max DAC A Register loaded with all 0s.
10 10 nA max
5 5 nA max DAC B Register loaded with all 0s.
10 10 nA max
REFERENCE INPUT
Input Resistance 9 9 kΩ min Typical Input Resistance = 14 kΩ.
20 20 kΩ max
, V
V
REFA
REFB
Input Resistance Match ±3 ±3 % max Typically ±0.5%.
DIGITAL INPUTS
(Input High Voltage) 2.4 2.4 V min
V
IH
(Input Low Voltage) 0.8 0.8 V max
V
IL
(Input Current)
I
IN
+25°C ±1 ±1 µA max V
to T
T
MIN
CIN (Input Capacitance)
MAX
2
±10 ± 10 µA max
10 10 pF max
= VDD.
IN
POWER SUPPLY
V
DD
I
DD
4.5/5.5 4.5/5.5 V min/V max
2 2 mA max
0.1 0.1 mA typ
AC PERFORMANCE CHARACTERISTICS
These characteristics are included for Design Guidance only and are not subject to test.
(VDD = 5 V; V
Parameter TA = 25C Unit Test Conditions/Comments
Output Current Settling Time 1 µs max To 0.01% of full-scale range. I
Digital-to-Analog Glitch lmpulse 2.5 nV-s typ Measured with V
AC Feedthrough
V
REFA
V
REFB
Power Supply Rejection
∆Gain/∆V
Output Capacitance
C
OUTA
C
OUTB
C
OUTA
C
OUTB
Channel-to-Channel Isolation
V
REFA
V
REFB
Digital Crosstalk 2.5 nV-s typ Measured for a Code Transition of all 0s to all 1s. I
Output Noise Voltage Density 25 nV/√Hz typ Measured between R
(10 Hz–100 kHz) is 10 Hz–100 kHz.
Total Harmonic Distortion –82 dB typ VIN = 6 V rms, 1 kHz. Both DACs loaded with all 1s.
NOTES
1
Temperature range as follows: A, B Versions: –40°C to +85°C.
2
Sample tested at 25°C to ensure compliance.
Specifications subject to change without notice.
to I
to I
to I
to I
REFA
OUTA
OUTB
DD
OUTB
OUTA
= V
= 10 V; I
REFB
= AGNDA = 0 V, I
OUTA
–70 dB max V
–70 dB max DAC registers loaded with all 0s.
= AGNDB = 0 V. Output Amplifiers are AD644 except where noted.)
OUTB
load = 100 Ω, C
REFB
OUT
= 0 V. I
measured from falling edge of WR. Typical Value of Settling Time is 0.6 µs.
= V
registers alternately loaded with all 0s and all 1s.
, V
REFA
REFA
= 20 V p-p 10 kHz sine wave.
REFB
±0.01 % per % max ∆VDD = VDD max – VDD min.
70 pF max DAC A, DAC B loaded with all 0s.
70 pF max
140 pF max DAC A, DAC B loaded with all 1s.
140 pF max
–84 dB typ V
–84 dB typ V
= 20 V p-p 10 kHz sine wave, V
REFA
= 20 V p-p 10 kHz sine wave, V
REFB
C
= 13 pF.
EXT
and I
FBA
OUTA
EXT
, I
load = 100 Ω, C
OUTB
= 0 V. Both DACs loaded with all 1s.
= 0 V. Both DACs loaded with all 1s.
OUTA
and I
. Frequency of measurement
OUTB
or R
OUTA
REFB
REFA
FBB
= 13 pF. DAC output
= 13 pF. DAC
EXT
, I
load = 100 Ω,
OUTB
–2–
REV. 0
AD7937
WARNING!
ESD SENSITIVE DEVICE
TIMING CHARACTERISTICS
(VDD = 5 V 10%, V
REFA
= V
= 10 V; I
REFB
= AGNDA = 0 V, I
OUTA
= AGNDB = 0 V.)
OUTB
Limit at
Limit at T
= –40C
A
Parameter TA = 25C to +85C Unit Test Conditions/Comments
t
1
t
2
t
3
t
4
t
5
t
6
t
7
t
8
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*
(TA = 25°C unless otherwise noted)
VDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, +17 V
, V
V
V
REFA
RFBA
to AGNDA, AGNDB . . . . . . . . . . . . . . . . ±25 V
REFB
, V
to AGNDA, AGNDB . . . . . . . . . . . . . . . . ±25 V
RFBB
Digital Input Voltage to DGND . . . . . . . –0.3 V, V
, I
I
OUTA
to DGND . . . . . . . . . . . . . . –0.3 V, VDD +0.3 V
OUTB
AGNDA, AGNDB to DGND . . . . . . . . . –0.3 V, V
SOIC Package
, Thermal Impedance . . . . . . . . . . . . . . . . . . . . 72°C/W
θ
JA
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . 300°C
IR Ref Low Peak Temperature . . . . . . . . . . . . . . . . . . 220°C
Operating Temperature Range
Industrial (A, B Versions) . . . . . . . . . . . . . –40°C to +85°C
10 10 ns min Address Valid to Write Setup Time
10 10 ns min Address Valid to Write Hold Time
20 40 ns min Data Setup Time
30 30 ns min Data Hold Time
0 0 ns min Chip Select or Update to Write Setup Time
0 0 ns min Chip Select or Update to Write Hold Time
115 125 ns min Write Pulsewidth
90 100 ns min Clear Pulsewidth
t
3
t
7
t
2
t
4
= tf = 20ns.
r
t
6
+0.3 V
DD
+0.3 V
DD
A0–A1
DATA
CS, UPD
WR
CLR
t
1
t
5
NOTES
1. ALL INPUT SIGNAL RISE AND FALL TIMES MEASURED
FROM 10% TO 90% OF +5V. t
2. TIMING MEASUREMENT REFERENCE LEVELS IS
Storage Temperature . . . . . . . . . . . . . . . . –65°C to +150°C
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; 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.
Figure 1. Timing Diagram
5V
0V
5V
0V
5V
0V
5V
0V
t
8
+ V
V
IH
5V
0V
IL
2
ORDERING GUIDE
Model Temperature Range Relative Accuracy Gain Error Package Description Option
AD7937AR –40°C to +85°C ±1 LSB ±6 LSB Small Outline R-24
AD7937BR –40°C to +85°C ± 1/2 LSB ±3 LSB Small Outline R-24
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 AD7937 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
–3–