AD AD7937BR Lc2mos 84 loading dual 12-bit dac Datasheet

a
LC2MOS
(8+4) Loading Dual 12-Bit DAC
AD7937
FUNCTIONAL BLOCK DIAGRAM
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
VDD
AD7937
DAC A MS
INPUT REG
DAC A LS
INPUT REG
4
8
DAC A REGISTER
UPD
12
IOUTA
DAC A
A1
AGNDA
RFBA
A0
VREFA
CONTROL
LOGIC
VREFB
CS
RFBB
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 (LC2MOS) process. It is speed compatible with most
microprocessors and accepts TTL, 74HC, and 5 V CMOS logic
level inputs.
WR
IOUTB
DAC B
AGNDB
12
CLR
DAC B REGISTER
DB7–DB0
4
8
DAC B MS
INPUT REG
DAC B LS
INPUT REG
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 VDD, with ± 10% tolerance on
this nominal figure. All specifications are guaranteed over
this range.
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
(VDD = 5 V 10%, VREFA = VREFB = 10 V; IOUTA = AGNDA = 0 V, IOUTB = AGNDB = 0 V. All
MIN to TMAX unless otherwise noted.)
AD7937–SPECIFICATIONS specifications T
Parameter
ACCURACY
Resolution
Relative Accuracy
Differential Nonlinearity
Gain Error
Gain Temperature Coefficient2;
∆Gain/∆Temperature
Output Leakage Current
IOUTA
IOUTB
REFERENCE INPUT
Input Resistance
VREFA, VREFB
Input Resistance Match
DIGITAL INPUTS
VIH (Input High Voltage)
VIL (Input Low Voltage)
IIN (Input Current)
+25°C
TMIN to TMAX
CIN (Input Capacitance)2
POWER SUPPLY
VDD
IDD
A Version
B Version
Unit
Test Conditions/Comments
12
±1
±1
±6
12
± 1/2
±1
±3
Bits
LSB max
LSB max
LSB max
All grades guaranteed monotonic over temperature.
Measured using RFBA, RFBB. Both DAC registers loaded with all 1s.
±5
±5
ppm/°C max
Typical value is 1 ppm/°C.
5
10
5
10
5
10
5
10
nA max
nA max
nA max
nA max
DAC A Register loaded with all 0s.
9
20
9
20
kΩ min
kΩ max
Typical Input Resistance = 14 kΩ.
±3
±3
% max
Typically ± 0.5%.
2.4
0.8
2.4
0.8
V min
V max
±1
± 10
10
±1
± 10
10
µA max
µA max
pF max
4.5/5.5
2
0.1
4.5/5.5
2
0.1
V min/V max
mA max
mA typ
DAC B Register loaded with all 0s.
VIN = VDD.
AC PERFORMANCE CHARACTERISTICS
These characteristics are included for Design Guidance only and are not subject to test.
(VDD = 5 V; VREFA = VREFB = 10 V; IOUTA = AGNDA = 0 V, IOUTB = AGNDB = 0 V. Output Amplifiers are AD644 except where noted.)
Parameter
TA = 25C
Unit
Test Conditions/Comments
Output Current Settling Time
1
µs max
To 0.01% of full-scale range. IOUT load = 100 Ω, CEXT = 13 pF. DAC output
measured from falling edge of WR. Typical Value of Settling Time is 0.6 µs.
Digital-to-Analog Glitch lmpulse
2.5
nV-s typ
Measured with VREFA = VREFB = 0 V. IOUTA, IOUTB load = 100 Ω, CEXT = 13 pF. DAC
registers alternately loaded with all 0s and all 1s.
AC Feedthrough
VREFA to IOUTA
VREFB to IOUTB
–70
–70
dB max
dB max
VREFA, VREFB = 20 V p-p 10 kHz sine wave.
DAC registers loaded with all 0s.
Power Supply Rejection
∆Gain/∆VDD
± 0.01
% per % max
∆VDD = VDD max – VDD min.
Output Capacitance
COUTA
COUTB
COUTA
COUTB
70
70
140
140
pF max
pF max
pF max
pF max
DAC A, DAC B loaded with all 0s.
Channel-to-Channel Isolation
VREFA to IOUTB
VREFB to IOUTA
–84
–84
dB typ
dB typ
VREFA = 20 V p-p 10 kHz sine wave, VREFB = 0 V. Both DACs loaded with all 1s.
VREFB = 20 V p-p 10 kHz sine wave, VREFA = 0 V. Both DACs loaded with all 1s.
Digital Crosstalk
2.5
nV-s typ
Measured for a Code Transition of all 0s to all 1s. IOUTA, IOUTB load = 100 Ω,
CEXT = 13 pF.
Output Noise Voltage Density
(10 Hz–100 kHz)
25
nV/√Hz typ
Measured between RFBA and IOUTA or RFBB and IOUTB. Frequency of measurement
is 10 Hz–100 kHz.
Total Harmonic Distortion
–82
dB typ
VIN = 6 V rms, 1 kHz. Both DACs loaded with all 1s.
DAC A, DAC B 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.
–2–
REV. 0
AD7937
TIMING CHARACTERISTICS
(VDD = 5 V 10%, VREFA = VREFB = 10 V; IOUTA = AGNDA = 0 V, IOUTB = AGNDB = 0 V.)
Parameter
Limit at
TA = 25C
Limit at
TA = –40C
to +85C
Unit
Test Conditions/Comments
t1
t2
t3
t4
t5
t6
t7
t8
10
10
20
30
0
0
115
90
10
10
40
30
0
0
125
100
ns min
ns min
ns min
ns min
ns min
ns min
ns min
ns min
Address Valid to Write Setup Time
Address Valid to Write Hold Time
Data Setup Time
Data Hold Time
Chip Select or Update to Write Setup Time
Chip Select or Update to Write Hold Time
Write Pulsewidth
Clear Pulsewidth
Specifications subject to change without notice.
t2
t1
ABSOLUTE MAXIMUM RATINGS*
5V
A0–A1
(TA = 25°C unless otherwise noted)
0V
t3
VDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, +17 V
VREFA, VREFB to AGNDA, AGNDB . . . . . . . . . . . . . . . . ± 25 V
VRFBA, VRFBB to AGNDA, AGNDB . . . . . . . . . . . . . . . . ± 25 V
Digital Input Voltage to DGND . . . . . . . –0.3 V, VDD +0.3 V
IOUTA, IOUTB to DGND . . . . . . . . . . . . . . –0.3 V, VDD +0.3 V
AGNDA, AGNDB to DGND . . . . . . . . . –0.3 V, VDD +0.3 V
SOIC Package
θJA, Thermal Impedance . . . . . . . . . . . . . . . . . . . . 72°C/W
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
Storage Temperature . . . . . . . . . . . . . . . . –65°C to +150°C
t4
5V
DATA
0V
t5
t6
5V
CS, UPD
0V
t7
5V
WR
0V
t8
CLR
5V
0V
NOTES
1. ALL INPUT SIGNAL RISE AND FALL TIMES MEASURED
FROM 10% TO 90% OF +5V. t r = t f = 20ns.
VIH + VIL
2. TIMING MEASUREMENT REFERENCE LEVELS IS
2
Figure 1. Timing Diagram
*Stresses above those listed under Absolute Maximum Ratings may cause permanent 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.
ORDERING GUIDE
Model
Temperature Range
Relative Accuracy
Gain Error
Package Description
Option
AD7937AR
AD7937BR
–40°C to +85°C
–40°C to +85°C
± 1 LSB
± 1/2 LSB
± 6 LSB
± 3 LSB
Small Outline
Small Outline
R-24
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–
WARNING!
ESD SENSITIVE DEVICE
AD7937
PIN FUNCTION DESCRIPTIONS
R
R
VREFA
Pin
Mnemonic
Description
1
2
3
4
5
6–11
13, 14
12
15
16
17
AGNDA
IOUTA
RFBA
VREFA
CS
DB0–DB7
Analog Ground for DAC A.
Current output terminal of DAC A.
Feedback resistor for DAC A.
Reference input to DAC A.
Chip Select Input Active low.
Eight data inputs, DB0–DB7.
DGND
A0
A1
CLR
18
19
WR
UPD
20
VDD
21
22
23
24
VREFB
RFBB
IOUTB
AGNDB
Digital Ground.
Address Line 0.
Address Line 1.
Clear Input. Active low. Clears all
registers.
Write Input. Active low.
Updates DAC Registers from inputs
registers.
Power supply input. Nominally 5 V to
15 V, with ± 10% tolerance.
Reference input to DAC B.
Feedback resistor for DAC B.
Current output terminal of DAC B.
Analog Ground for DAC B.
24
AGNDB
IOUTA 2
23
IOUTB
RFBA 3
22
RFBB
VREFA 4
21
VREFB
20
VDD
19
UPD
CS 5
DB0
6
DB1
7
DB2
AD7937
8
17
CLR
16
A1
DB4 10
15
A0
DB5 11
14
DB7
DGND 12
13
DB6
2R
S11
S10
S0
2R
RFBA
IOUTA
AGNDA
Figure 2. Simplified Circuit Diagram for DAC A
EQUIVALENT CIRCUIT ANALYSIS
Figure 3 shows the equivalent circuit for one of the D/A converters (DAC A) in the AD7937. A similar equivalent circuit
can be drawn for DAC B.
R
RFBA
IOUTA
VREFA
D.VREF
R
R
RO
ILKG
COUT
AGNDA
Figure 3. Equivalent Analog Circuit for DAC A
COUT is the output capacitance due to the N-channel switches
and varies from about 50 pF to 100 pF with digital input code.
The current source ILKG is composed of surface and junction
leakages and approximately doubles every 10°C. RO is the equivalent output resistance of the device which varies with input code.
DIGITAL CIRCUIT INFORMATION
The digital inputs are designed to be both TTL and 5 V CMOS
compatible. All logic inputs are static protected MOS gates with
typical input currents of less than 1 nA.
Table I. AD7937 Truth Table
CLR UPD CS WR A1 A0 Function
TOP VIEW
(Not to Scale) 18 WR
DB3 9
2R
R
PIN CONFIGURATION
SOIC
AGNDA 1
2R
CIRCUIT INFORMATION – D/A SECTION
The AD7937 contains two identical 12-bit multiplying D/A
converters. Each DAC consists of a highly stable R-2R ladder
and 12 N-channel current steering switches. Figure 2 shows a
simplified D/A circuit for DAC A. In the R-2R ladder, binary
weighted currents are steered between IOUTA and AGNDA. The
current flowing in each ladder leg is constant, irrespective of
switch state. The feedback resistor RFBA is used with an op amp
(see Figures 4 and 5) to convert the current flowing in IOUTA to
a voltage output.
1
1
0
1
1
1
X
1
1
X
X
0
X
1
X
0
X
X
X
0
X
X
X
0
1
1
0
0
0
1
1
1
0
0
1
0
1
1
0
0
1
1
1
0
1
0
X
X
1
0
0
0
X
X
No Data Transfer
No Data Transfer
All Registers Cleared
DAC A LS Input Register
Loaded with DB7–DB0 (LSB)
DAC A MS Input Register
Loaded with DB3 (MSB)–DB0
DAC B LS Input Register
Loaded with DB7–DB0 (LSB)
DAC B MS Input Register
Loaded with DB3 (MSB)–DB0
DAC A, DAC B Registers
Updated Simultaneously from
Input Registers
DAC A, DAC B Registers are
Transparent
NOTE: X = Don’t care
–4–
REV. 0
AD7937
UNIPOLAR BINARY OPERATION
(2-QUADRANT MULTIPLICATION)
BIPOLAR OPERATION
(4-QUADRANT MULTIPLICATION)
Figure 4 shows the circuit diagram for unipolar binary operation.
With an ac input, the circuit performs 2-quadrant multiplication.
The code table for Figure 4 is given in Table II.
The recommended circuit diagram for bipolar operation is shown
in Figure 5. Offset binary coding is used.
Operational amplifiers A1 and A2 can be in a single package
(AD644, AD712) or separate packages (AD544, AD711,
AD OP27). Capacitors C1 and C2 provide phase compensation
to help prevent overshoot and ringing when high-speed op amps
are used.
For zero offset adjustment, the appropriate DAC register is loaded
with all 0s and amplifier offset adjusted so that VOUTA or VOUTB
is 0 V. Full-scale trimming is accomplished by loading the DAC
register with all 1s and adjusting R1 (R3) so that VOUTA (VOUTB)
= –VIN (4095/4096). For high temperature operation, resistors
and potentiometers should have a low Temperature Coefficient.
In many applications, because of the excellent Gain T.C. and Gain
Error specifications of the AD7937, Gain Error trimming is not
necessary. In fixed reference applications, full scale can also be
adjusted by omitting R1, R2, R3, R4 and trimming the reference
voltage magnitude.
With the appropriate DAC register loaded to 1000 0000 0000,
adjust R1 (R3) so that VOUTA (VOUTB) = 0 V. Alternatively, R1,
R2 (R3, R4) may be omitted and the ratios of R6, R7 (R9, R10)
varied for VOUTA (VOUTB) = 0 V. Full-scale trimming can be
accomplished by adjusting the amplitude of VIN or by varying the
value of R5 (R8).
If R1, R2 (R3, R4) are not used, then resistors R5, R6, R7 (R8,
R9, R10) should be ratio matched to 0.01% to ensure gain error
performance to the data sheet specification. When operating over a
wide temperature range, it is important that the resistors be of
the same type so that their temperature coefficients match.
The code table for Figure 5 is given in Table III.
R2
47
C1
33pF
IOUTA
RFBB
DAC B
DGND
VOUTB
1/2
AD712
DGND
R3
100
C2
33pF
1/2
AD712
A3
AGNDB
R9
10k
A2
AGNDB
1/2
AD712
R4
RFBB 47
IOUTB
DB0
R10
20k
R3
100
VINB
1/2
AD712
A1
AGNDA
C2
33pF
IOUTB
DAC B
VOUTA
1/2
AD712
R4
47
DAC A
AD7937*
DATA
INPUT
A1
AGNDA
AD7937*
DB0
DB7
A2
C1
33pF
IOUTA
RFBA
DATA
INPUT
VOUTA
R7
10k
R2
RFBA 47
R1
100
DB7
R6
20k
R1
100
VDD VINA
DAC A
R5
20k
VDD VINA
*CONTROL CIRCUITRY
R8
20k
VOUTB
A4
1/2
AD712
OMITTED FOR CLARITY
*CONTROL CIRCUITRY
Figure 5. Bipolar Operation (Offset Binary Coding)
OMITTED FOR CLARITY
VINB
Table III. Bipolar Code Table for Offset Binary
Circuit of Figure 5
Figure 4. Unipolar Binary Operation
Table II. Unipolar Binary Code Table for
Circuit of Figure 4
Binary Number in
DAC Register
MSB
LSB
1111 1111 1111
Binary Number in
DAC Register
MSB
LSB
Analog Output,
VOUTA or VOUTB
 4095 
−V IN 

 4096 
Analog Output,
VOUTA or VOUTB
1111 1111 1111
 2047 
+V IN 

 2048 
1000 0000 0001
 1 
+V IN 

 2048 
1000 0000 0000
0V
1000 0000 0000
 2048 
−V IN 
 = − 12 V IN
 4096 
0111 1111 1111
0000 0000 0001
 1 
−V IN 

 4096 
 1 
−V IN 

 2048 
0000 0000 0000
0V
0000 0000 0000
 2048 
−V IN 
 = −V IN
 2048 
REV. 0
–5–
AD7937
SEPARATE AGND PINS
PROGRAMMABLE OSCILLATOR
The DACs in the AD7937 have separate AGND lines taken to
pins AGNDA and AGNDB on the package. This increases the
applications versatility of the part. Figure 6 is an example of this.
DAC A is connected in standard fashion as a programmable
attenuator. AGNDA is at ground potential. DAC B is operating
with AGND B biased to 5 V by the AD584. This gives an output range of 5 V to 10 V.
Figure 7 shows a conventional state variable oscillator in which
the AD7937 controls the programmable integrators. The frequency
of oscillation is given by:
f=
RFBA
f=
IOUTA
VREFA
DAC A
AGNDA
A1
VOUTA
Since REQ =
DB7
DATA
INPUT
AD7937*
DB0
RFBB
IOUTB
VREFB
DAC B
AGNDB
DGND
VOUTB = 5V
TO 10V
5V
1
REQ1 × REQ2
(N / 2n )2
RLAD1 × RLAD2
1 1
×
2π C
=
1 D
×
2π C
=
1
D
×
2 π C × RLAD
1
RLAD1 × RLAD2
N
D= n
2 
VDD
AD584
SIGNAL
GROUND
1 1
×
2π C
2n × RLAD
, (RLAD = DAC ladder resistance).
N
f=
A2
R6 ×
1
R5 C1× C2 × REQ1 × REQ2
where REQ1 and REQ2 are the equivalent resistances of the DACs.
The same digital code is loaded into both DACs. If C1 = C2
and R5 = R6, the expression reduces to
VDD = 5V
20V p–p
1
2π
*CONTROL CIRCUITRY OMITTED FOR CLARITY
Figure 6. DACs Used in Different Modes
m
where m is the DAC ladder resistance mismatch ratio, typically
1.005.
With the values shown in Figure 7, the output frequency varies
from 0 Hz to 1.38 kHz. The amplitude of the output signal at
the A3 output is 10 V peak-to-peak and is constant over the
entire frequency span.
FREQUENCY
SELECT CODE
R5
10k
R4
200k
R6
10k
C1
10,000pF
C2
10,000pF
1/2 AD7937
A1
AD711
VREFA
IOUTA
1/2 AD7937
A2
VREFB
AGNDA
DAC A
1/2
AD712
IOUTB
A3
AGNDB
DAC B
VOUT
1/2
AD712
5.1V
NOTE
DAC CONTROL INPUTS OMITTED FOR CLARITY
10k
Figure 7. Programmable State Variable Oscillator
–6–
REV. 0
AD7937
APPLICATION HINTS
MICROPROCESSOR INTERFACING
Output Offset: CMOS D/A converters in circuits such as Figures 4 and 5 exhibit a code-dependent output resistance which
in turn can cause a code-dependent error voltage at the output
of the amplifier. The maximum amplitude of this error, which
adds to the D/A converter nonlinearity, depends on VOS, where
VOS is the amplifier input offset voltage. To maintain specified
operation, it is recommended that VOS be no greater than
(25 ⫻ 10–6) (VREF) over the temperature range of operation.
Suitable op amps are the AD711C and its dual version, the
AD712C. These op amps have a wide bandwidth and high slew
rate and are recommended for wide bandwidth ac applications.
AD711/AD712 settling time to 0.01% is typically 3 µs.
The byte loading structure of the AD7937 makes it very easy to
interface the device to any 8-bit microprocessor system. Figure
8 shows an example 8-bit interface between the AD7937 and a
generic 8-bit microcontroller/DSP processor. Pins D7 to D0 of
the processor are connected to pins D7 to D0 of the AD7937.
When writing to the DACs, the lower 8 bits must be written
first, followed by the upper four bits. The upper four bits should
be output on data lines D0 to D3.
CONTROLLER/
DSP PROCESSOR *
Temperature Coefficients: The gain temperature coefficient
of the AD7937 has a maximum value of 5 ppm/°C and typical
value of 1 ppm/°C. This corresponds to worst case gain shifts of
2 LSBs and 0.4 LSBs respectively over a 100°C temperature range.
When trim resistors R1 (R3) and R2 (R4) are used to adjust full
scale range as in Figure 4, the temperature coefficient of R1 (R3)
and R2 (R4) should also be taken into account.
AD7937*
CLR
D7
D7
D0
D0
DATA
BUS
UPPER BITS
OF ADDRESS
BUS
High Frequency Considerations: AD7937 output capacitance
works in conjunction with the amplifier feedback resistance to
add a pole to the open-loop response. This can cause ringing or
oscillation. Stability can be restored by adding a phase compensation capacitor in parallel with the feedback resistor. This is
shown as C1 and C2 in Figures 4 and 5.
ADDRESS
DECODE
CS
UPD
A0
A0
A1
A1
R/W
WR
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 8. AD7937 8-Bit Interface
Feedthrough: The dynamic performance of the AD7937 depends
upon the gain and phase stability of the output amplifier, together
with the optimum choice of PC board layout and decoupling
components.
REV. 0
FROM
SYSTEM
RESET
–7–
AD7937
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
24-Lead Small Outline SOIC
(R-24)
24
C01010–2.5–7/00 (rev. 0)
0.6141 (15.60)
0.5985 (15.20)
13
0.2992 (7.60)
0.2914 (7.40)
PIN 1
0.0118 (0.30) 0.0500
0.0040 (0.10) (1.27)
BSC
12
0.4193 (10.65)
0.3937 (10.00)
0.1043 (2.65)
0.0926 (2.35)
8
0
0.0192 (0.49) SEATING
0.0125
(0.32)
0.0138 (0.35) PLANE
0.0091 (0.23)
0.0291 (0.74)
45
0.0098 (0.25)
0.0500 (1.27)
0.0157 (0.40)
PRINTED IN U.S.A.
1
–8–
REV. 0
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