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FEATURES Two 12-Bit DACs in One Package DAC Ladder Resistance Matching: 0.5% Space Saving Skinny DIP and Surface Mount Packages 4-Quadrant Multiplication Low Gain Error (1 LSB max Over Temperature) Byte Loading Structure Fast Interface Timing APPLICATIONS Automatic Test Equipment Programmable Filters Audio Applications Synchro Applications Process Control
LC2MOS (8+4) Loading Dual 12-Bit DAC AD7537
FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The AD7537 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 AD7537 has a 2-byte (8 LSBs, 4 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 AD7537 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 AD7537 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.
PRODUCT HIGHLIGHTS
1. DAC to DAC Matching: Since both DACs are fabricated on the same chip, precise matching and tracking is inherent. Many applications which are not practical using two discrete DACs are now possible. Typical matching: 0.5%. 2. Small Package Size: The AD7537 is packaged in small 24-pin 0.3" DIPs and in 28-terminal surface mount packages. 3. Wide Power Supply Tolerance: The device operates on a +12 V to +15 V VDD, with 10% tolerance on this nominal figure. All specifications are guaranteed over this range.
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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
AD7537-SPECIFICATIONS
Parameter ACCURACY Resolution Relative Accuracy Differential Nonlinearity Gain Error Gain Temperature Coefficient2; Gain/Temperature Output Leakage Current IOUTA +25C TMIN to TMAX IOUTB +25C TMIN to TMAX REFERENCE INPUT Input Resistance VREFA, VREFB Input Resistance Match DIGITAL INPUTS VIH (lnput High Voltage) VIIL (Input Low Voltage) IIN (Input Current) +25C TMIN to TMAX CIN (lnput Capacitance)2 POWER SUPPLY3 VDD IDD J, A Versions 12 1 1 6 K, B Versions 12 1/2 1 3
(VDD = +12 V to +15 V, 10%, VREFA = VREFB = 10 V; IOUTA = AGND = 0 V, IOUTB = AGNDB = 0 V. All specifications TMIN to TMAX unless otherwise noted.)
L, C Versions 12 1/2 1 1 S Version 12 1 1 6 T Version 12 1/2 1 3 U Version 12 1/2 1 2
Units Bits LSB max LSB max LSB max
Test Conditions/Comments
All grades guaranteed monotonic over temperature. Measured using RFBA, RFBB. Both DAC registers loaded with all 1s.
5 10 150 10 150 9 20 3 2.4 0.8 1 10 10 10.8/16.5 2
5 10 150 10 150 9 20 3 2.4 0.8 1 10 10 10.8/16.5 2
5 10 150 10 150 9 20 1 2.4 0.8 1 10 10 10.8/16.5 2
5 10 250 10 250 9 20 3 2.4 0.8 1 10 10 10.8/16.5 2
5 10 250 10 250 9 20 3 2.4 0.8 1 10 10 10.8/16.5 2
5 10 250 10 250 9 20 1 2.4 0.8 1 10 10 10.8/16.5 2
ppm/C max Typical value is 1 ppm/C nA max nA max nA max nA max k min k max % max V min V max A max A max pF max V min/V max mA max VIN = VDD DAC A Register loaded with all 0s DAC B Register loaded with all 0s Typical Input Resistance = 14 k Typically 0.5%
AC PERFORMANCE CHARACTERISTICS
These characteristics are included for Design Guidance only and are not subject to test. (VDD = +12 V to +15 V; VREFA = VREFB = +10 V; IOUTA = AGNDA = 0 V, IOUTB = AGNDB = 0 V. Output Amplifiers are AD644 except where noted.)
Parameter Output Current Settling Time TA = +25 C 1.5 TA = TMIN, TMAX Units s max Test Conditions/Comments To 0.01% of full-scale range. IOUT load = 100 , CEXT = 13 pF. DAC output measured from falling edge of WR. Typical Value of Settling Time is 0.8 s. Measured with VREFA = VREFB = 0 V. IOUTA, IOUTB load = 100 , CEXT = 13 pF. DAC registers alternately loaded with all 0s and all 1s. VREFA, VREFB = 20 V p-p 10 kHz sine wave. DAC registers loaded with all 0s.
Digital-to-Analog Glitch lmpulse AC Feedthrough4 VREFA to IOUTA VREFB to IOUTB Power Supply Rejection Gain/VDD Output Capacitance COUTA COUTB COUTA COUTB Channel-to-Channel Isolation VREFA to IOUTB VREFB to IOUTA Digital Crosstalk Output Noise Voltage Density (10 Hz-100 kHz) Total Harmonic Distortion
NOTES 1 Temperature range as follows:
7
nV-s typ
-70 -70 0.01 70 70 140 140 -84 -84 7 25 -82
-65 -65 0.02 70 70 140 140
dB max dB max
% per % max VDD = VDD max - VDD min pF max pF max pF max pF max dB typ dB typ nV-s typ nV/Hz typ dB typ
2 3
DAC A, DAC B loaded with all 0s DAC A, DAC B loaded with all 1s
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. Measured for a Code Transition of all 0s to all 1s. IOUTA, IOUTB load = 100 , CEXT = 13 pF. Measured between RFBA and IOUTA or RFBB and IOUTB. Frequency of measurement is 10 Hz-100 kHz. VIN = 6 V rms, 1 kHz. Both DACs loaded with all 1s.
J, K, L Versions: -40C to +85C; A, B, C Versions: -40C to +85C; S, T, U Versions: -55C to +125C Specifications subject to change without notice.
Sample tested at +25C to ensure compliance. Functional at VDD = 5 V, with degraded specifications. 4 Pin 12 (DGND) on ceramic DIPs is connected to lid.
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AD7537 TIMING CHARACTERISTICS
Parameter t1 t2 t3 t4 t5 t6 t7 t8 Limit at TA = +25 C 15 15 60 25 0 0 80 80
(VDD = +10.8 V to +16.5 V, VREFA = VREFB = +10 V; IOUTA = AGNDA = 0 V, IOUTB = AGNDB = 0 V.)
Limit at TA = +55 C to +125 C 30 25 80 25 0 0 100 100
Limit at TA = -40 C to +85 C 15 15 80 25 0 0 80 80
Units ns min ns min ns min ns min ns min ns min ns min ns min
Test Conditions/Comments 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 Pulse Width Clear Pulse Width
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*
(TA = +25C unless otherwise stated)
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 Power Dissipation (Any Package) To +75C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 mW Derates Above +75C . . . . . . . . . . . . . . . . . . . . . 6 mW/C
Operating Temperature Range Commercial Plastic (J, K, L Versions) . . . . -40C to +85C Industrial Hermetic (A, B, C Versions) . . . -40C to +85C Extended Hermetic (S, T, U Versions) . . -55C to +125C Storage Temperature . . . . . . . . . . . . . . . . -65C to +150C Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . +300C
*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.
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 AD7537 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
ORDERING GUIDE1
Model2 AD7537JN AD7537KN AD7537LN AD7537JP AD7537KP AD7537LP AD7537AQ AD7537BQ AD7537CQ AD7537SQ AD7537TQ AD7537UQ AD7537SE AD7537TE AD7537UE
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -55C to +125C -55C to +125C -55C to +125C -55C to +125C -55C to +125C -55C to +125C
Relative Gain Accuracy Error 1 LSB 1/2 LSB 1/2 LSB 1 LSB 1/2 LSB 1/2 LSB 1 LSB 1/2 LSB 1/2 LSB 1 LSB 1/2 LSB 1/2 LSB 1 LSB 1/2 LSB 1/2 LSB 6 LSB 3 LSB 1 LSB 6 LSB 3 LSB 1 LSB 6 LSB 3 LSB 1 LSB 6 LSB 3 LSB 2 LSB 6 LSB 3 LSB 2 LSB
Package Option3 N-24 N-24 N-24 P-28A P-28A P-28A Q-24 Q-24 Q-24 Q-24 Q-24 Q-24 E-28A E-28A E-28A
Figure 1. Timing Diagram
NOTES 1 Analog Devices reserves the right to ship ceramic packages (D-24A) in lieu of cerdip packages (Q-24). 2 To order MIL-STD-883, Class B processed parts, add/883B to part number. Contact your local sales office for military data sheet. 3 E = Leadless Ceramic Chip Carrier; N = Plastic DIP; P = Plastic Leaded Chip Carrier; Q = Cerdip.
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AD7537
PIN FUNCTION DESCRIPTION (DIP)
PIN 1 2 3 4 5 6-14 12 15 16 17 18 19 20 21 22 23 24
MNEMONIC AGNDA IOUTA RFBA VREFA CS DB0-DB7 DGND A0 A1 CLR WR UPD VDD VREFB RFBB IOUTB AGNDB
DESCRIPTION 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. 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 +12 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.
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.
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 AD7537. A similar equivalent circuit can be drawn for DAC B. COUT is the output capacitance due to the N-channel switches and varies from about 50 pF to 150 pF with digital input code. The current source ILKG is composed of surface and junction leakages and approximately doubles every 10C. R0 is the equivalent output resistance of the device which varies with input code.
DIGITAL CIRCUIT INFORMATION
PIN CONFIGURATIONS DIP LCCC
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. AD7537 Truth Table
CLR UPD CS WR A1 A0 FUNCTION 1 1 0 1
PLCC
1 1 X 1 1 1 1 0
1 X X 0 0 0 0 1
X 1 X 0 0 0 0 0
X X X 0 0 1 1 X
X X X 0 1 0 1 X
1 1 1 1
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
NOTES: X = Don't care
CIRCUIT INFORMATION - D/A SECTION
The AD7537 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 -4-
Figure 3. Equivalent Analog Circuit for DAC A
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Applications-AD7537
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. 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 AD7537, 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.
The recommended circuit diagram for bipolar operation is shown in Figure 5. Offset binary coding is used. 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, 10) 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.
Figure 5. Bipolar Operation (Offset Binary Coding)
Table III. Bipolar Code Table for Offset Binary Circuit of Figure 5
Figure 4. AD7537 Unipolar Binary Operation
Table II. Unipolar Binary Code Table for Circuit of Figure 4
Binary Number in DAC Register MSB LSB
Analog Output, VOUTA or VOUTB
2047 +V IN 2048 1 +V IN 2048
1111 1111 1111
Binary Number in DAC Register MSB LSB
Analog Output, VOUTA or VOUTB
1000 0000 0001 1000 0000 0000 0111 1111 1111
1111 1111 1111
4095 -V IN 4096 2048 -V IN = - 12 V IN 4096 1 -V IN 4096
0V -5-
0V
1 -V IN 2048 2048 -V IN = -V IN 2048
1000 0000 0000
0000 0000 0000
0000 0000 0001 0000 0000 0000 REV. 0
AD7537
SEPARATE AGND PINS
The DACs in the AD7537 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.
the AD7537 controls the programmable integrators. The frequency of oscillation is given by: f= 1 2 R6 x 1 R5 C1x C2 x REQ1 x 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 f= 11 x 2 C 1 REQ1 x REQ2
Since REQ =
2n x RLAD , (RLAD = DAC ladder resistance). N f= 11 x 2 C (N / 2n )2 RLAD1 x RLAD2 1 RLAD1 x RLAD2 N D= n 2
= =
1D x 2 C
D 1 x 2 C x RLAD
m
where m is the DAC ladder resistance mismatch ratio, typically 1.005.
Figure 6. AD7537 DACs Used in Different Modes
PROGRAMMABLE OSCILLATOR
Figure 7 shows a conventional state variable oscillator in which
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.
Figure 7. Programmable State Variable Oscillator
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AD7537
APPLICATION HINTS
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 s. Temperature Coefficients: The gain temperature coefficient of the AD7537 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 100C 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. For further information see "Gain Error and Gain Temperature Coefficient of CMOS Multiplying DACs", Application Note, Publication Number E630c-5-3/86 available from Analog Devices. High Frequency Considerations: AD7537 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. Feedthrough: The dynamic performance of the AD7537 depends upon the gain and phase stability of the output amplifier, together with the optimum choice of PC board layout and decoupling components. A suggested printed circuit layout for Figure 4 is shown in Figure 8 which minimizes feedthrough from VREFA, VREFB to the output in multiplying applications.
other for the MC68008. Figure 11 shows how an AD7537 system can be easily expanded by tying all the UPD lines together and using a single decoder output to control these. This expanded system is shown using a Z80 microprocessor but it is just as easily configured using any other 8-bit microprocessor system. Note how the system shown in Figure 11 produces 4 analog outputs with a minimum amount of hardware.
Figure 9. AD7537-MC6809 Interface
Figure 10. AD7537-MC68008 Interface
Figure 8. Suggested Layout for AD7537
MICROPROCESSOR INTERFACING
The byte loading structure of the AD7537 makes it very easy to interface the device to any 8-bit microprocessor system. Figures 9 and 10 show two interfaces: one for the MC6809 and the REV. 0 -7-
Figure 11. Expanded AD7537 System
AD7537
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
24-Pin Plastic DIP (N-24)
24-Pin Ceramic DIP (D-24A)
24-Pin Cerdip (Q-24)
28-Terminal Leadless Ceramic Chip Carrier (E-28A)
28-Terminal Plastic Leaded Chip Carrier (P-28A)
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PRINTED IN U.S.A.
C978a-5-10/87

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