AD AD7528TQ Cmos dual 8-bit buffered multiplying dac Datasheet

a
FEATURES
On-Chip Latches for Both DACs
+5 V to +15 V Operation
DACs Matched to 1%
Four Quadrant Multiplication
TTL/CMOS Compatible
Latch Free (Protection Schottkys not Required)
APPLICATIONS
Digital Control of:
Gain/Attenuation
Filter Parameters
Stereo Audio Circuits
X-Y Graphics
CMOS Dual 8-Bit
Buffered Multiplying DAC
AD7528
FUNCTIONAL BLOCK DIAGRAM
VREF A
RFB A
VDD
DB0
DATA
INPUTS
DB7
INPUT
BUFFER
OUT A
LATCH
DAC A
AGND
AD7528
DAC A/
DAC B
CS
RFB B
CONTROL
LOGIC
OUT B
WR
LATCH
DAC B
DGND
VREF B
ORDERING GUIDE1
GENERAL DESCRIPTION
The AD7528 is a monolithic dual 8-bit digital/analog converter
featuring excellent DAC-to-DAC matching. It is available in
skinny 0.3" wide 20-lead DIPs and in 20-lead surface mount
packages.
Separate on-chip latches are provided for each DAC to allow
easy microprocessor interface.
Data is transferred into either of the two DAC data latches via a
common 8-bit TTL/CMOS compatible input port. Control
input DAC A/DAC B determines which DAC is to be loaded.
The AD7528’s load cycle is similar to the write cycle of a random access memory and the device is bus compatible with most
8-bit microprocessors, including 6800, 8080, 8085, Z80.
The device operates from a +5 V to +15 V power supply, dissipating only 20 mW of power.
Both DACs offer excellent four quadrant multiplication characteristics with a separate reference input and feedback resistor for
each DAC.
PRODUCT HIGHLIGHTS
1. DAC-to-DAC matching: since both of the AD7528 DACs are
fabricated at the same time on the same chip, precise matching and tracking between DAC A and DAC B is inherent.
The AD7528’s matched CMOS DACs make a whole new
range of applications circuits possible, particularly in the
audio, graphics and process control areas.
Model2
Temperature
Ranges
Relative Gain
Accuracy Error
Package
Options 3
AD7528JN
AD7528KN
AD7528LN
AD7528JP
AD7528KP
AD7528LP
AD7528JR
AD7528KR
AD7528LR
AD7528AQ
AD7528BQ
AD7528CQ
AD7528SQ
AD7528TQ
AD7528UQ
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–55°C to +125°C
–55°C to +125°C
–55°C to +125°C
± 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
N-20
N-20
N-20
P-20A
P-20A
P-20A
R-20
R-20
R-20
Q-20
Q-20
Q-20
Q-20
Q-20
Q-20
± 4 LSB
± 2 LSB
± 1 LSB
± 4 LSB
± 2 LSB
± 1 LSB
± 4 LSB
± 2 LSB
± 1 LSB
± 4 LSB
± 2 LSB
± 1 LSB
± 4 LSB
± 2 LSB
± 1 LSB
NOTES
1
Analog Devices reserves the right to ship side-brazed ceramic in lieu of cerdip. Parts
will be marked with cerdip designator “Q.”
2
Processing to MIL-STD-883C, Class B is available. To order, add suffix “/883B” to
part number. For further information, see Analog Devices’ 1990 Military Products
Databook.
3
N = Plastic DIP; P = Plastic Leaded Chip Carrier; Q = Cerdip; R = SOIC.
2. Small package size: combining the inputs to the on-chip DAC
latches into a common data bus and adding a DAC A/DAC B
select line has allowed the AD7528 to be packaged in either a
small 20-lead DIP, SOIC or PLCC.
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: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998
AD7528–SPECIFICATIONS (V
REF A
= VREF B = +10 V; OUT A = OUT B = O V unless otherwise noted)
V DD = +5 V
Parameter
STATIC PERFORMANCE2
Resolution
Relative Accuracy
Differential Nonlinearity
Gain Error
TA = +25°C
TMIN, TMAX
TA= +25°C TMIN, TMAX
Units
All
J, A, S
K, B, T
L, C, U
All
8
±1
± 1/2
± 1/2
±1
8
±1
± 1/2
± 1/2
±1
8
±1
± 1/2
± 1/2
±1
8
±1
± 1/2
± 1/2
±1
Bits
LSB max
LSB max
LSB max
LSB max
J, A, S
K, B, T
L, C, U
±4
±2
±1
±6
±4
±3
±4
±2
±1
±5
±3
±1
LSB max
LSB max
LSB max
All
± 0.007
± 0.007
± 0.0035
± 0.0035
%/°C max
All
All
All
± 50
± 50
8
15
± 400
± 400
8
15
± 50
± 50
8
15
± 200
± 200
8
15
nA max
nA max
kΩ min
kΩ max
All
±1
±1
±1
±1
% max
All
2.4
2.4
13.5
13.5
V min
All
0.8
0.8
1.5
1.5
V max
All
±1
± 10
±1
± 10
µA max
All
All
10
15
10
15
10
15
10
15
pF max
pF max
Gain Temperature Coefficient3
∆Gain/∆Temperature
Output Leakage Current
OUT A (Pin 2)
OUT B (Pin 20)
Input Resistance (V REF A, V REF B)
VREF A/V REF B Input Resistance
Match
DIGITAL INPUTS4
Input High Voltage
VIH
Input Low Voltage
VIL
Input Current
IIN
Input Capacitance
DB0–DB7
WR, CS, DAC A/DAC B
SWITCHING CHARACTERISTICS 3
Chip Select to Write Set Up Time
tCS
Chip Select to Write Hold Time
tCH
DAC Select to Write Set Up Time
tAS
DAC Select to Write Hold Time
tAH
Data Valid to Write Set Up Time
tDS
Data Valid to Write Hold Time
tDH
Write Pulsewidth
tWR
POWER SUPPLY
IDD
VDD = +15 V
Version1
Test Conditions/Comments
This is an Endpoint Linearity Specification
All Grades Guaranteed Monotonic Over
Full Operating Temperature Range
Measured Using Internal R FB A and RFB B
Both DAC Latches Loaded with 11111111
Gain Error is Adjustable Using Circuits
of Figures 4 and 5
DAC Latches Loaded with 00000000
Input Resistance TC = –300 ppm/°C, Typical
Input Resistance is 11 kΩ
VIN = 0 or V DD
See Timing Diagram
All
90
100
60
80
ns min
All
0
0
10
15
ns min
All
90
100
60
80
ns min
All
0
0
10
15
ns min
All
80
90
30
40
ns min
All
0
0
0
0
ns min
All
90
100
60
80
ns min
All
All
2
100
2
500
2
100
2
500
mA max
µA max
See Figure 3
All Digital Inputs VIL or VIH
All Digital Inputs 0 V or V DD
(Measured Using Recommended P.C. Board Layout (Figure 7) and AD644 as
AC PERFORMANCE CHARACTERISTICS5 Output Amplifiers)
V DD = +5 V
VDD = +15 V
Parameter
Version1 TA = +25°C
TMIN, TMAX TA= +25°C TMIN, TMAX Units
Test Conditions/Comments
DC SUPPLY REJECTION (∆GAIN/∆VDD)
All
0.02
0.04
0.01
0.02
% per % max ∆V DD = ± 5%
CURRENT SETTLING TIME2
All
350
400
180
200
ns max
PROPAGATION DELAY (From Digital Input to 90% of Final Analog Output Current)
All
220
270
80
100
ns max
DIGITAL-TO-ANALOG GLITCH IMPULSE All
160
OUTPUT CAPACITANCE
COUT A
COUT B
COUT A
COUT B
50
50
120
120
50
50
120
120
50
50
120
120
–70
–70
–65
–65
–70
–70
AC FEEDTHROUGH 6
VREF A to OUT A
VREF B to OUT B
All
All
440
–2–
To 1/2 LSB. OUT A/OUT B Load = 100 Ω.
WR = CS = 0 V. DB0–DB7 = 0 V to VDD or
VDD to 0 V
VREF A = VREF B = +10 V
OUT A, OUT B Load = 100 Ω C EXT = 13 pF
WR = CS = 0 V DB0–DB7 = 0 V to VDD or
VDD to 0 V
nV sec typ
For Code Transition 00000000 to 11111111
50
50
120
120
pF max
pF max
pF max
pF max
DAC Latches Loaded with 00000000
–65
–65
dB max
dB max
VREF A, VREF B = 20 V p-p Sine Wave
@ 100 kHz
DAC Latches Loaded with 11111111
REV. B
AD7528
V DD = +5 V
Parameter
Version1 TA = +25°C
CHANNEL-TO-CHANNEL ISOLATION
VREF A to OUT B
All
VREF B to OUT A
VDD = +15 V
TMIN, TMAX TA= +25°C TMIN, TMAX Units
Test Conditions/Comments
–77
–77
dB typ
–77
–77
dB typ
Both DAC Latches Loaded with 11111111.
VREF A = 20 V p-p Sine Wave @ 100 kHz
VREF B = 0 V see Figure 6.
VREF A = 20 V p-p Sine Wave @ 100 kHz
VREF A = 0 V see Figure 6.
DIGITAL CROSSTALK
All
30
60
nV sec typ
Measured for Code Transition 00000000 to
11111111
HARMONIC DISTORTlON
All
–85
–85
dB typ
VIN = 6 V rms @ 1 kHz
NOTES
1
Temperature Ranges are J, K, L Versions: –40°C to +85°C
A, B, C Versions: –40°C to +85°C
S, T, U Versions: –55°C to +125°C
2
Specifications applies to both DACs in AD7528.
3
Guaranteed by design but not production tested.
4
Logic inputs are MOS Gates. Typical input current (+25°C) is less than 1 nA.
5
These characteristics are for design guidance only and are not subject to test.
6
Feedthrough can be further reduced by connecting the metal lid on the ceramic package
(suffix D) to DGND.
AD7528, ideal maximum output is VREF – 1 LSB. Gain error of
both DACs is adjustable to zero with external resistance.
Output Capacitance
Capacitance from OUT A or OUT B to AGND.
Digital to Analog Glitch lmpulse
The amount of charge injected from the digital inputs to the
analog output when the inputs change state. This is normally
specified as the area of the glitch in either pA-secs or nV-secs
depending upon whether the glitch is measured as a current or
voltage signal. Glitch impulse is measured with VREF A,
VREF B = AGND.
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS
(TA = +25°C unless otherwise noted)
VDD to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V, +17 V
VDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V, +17 V
AGND to DGND . . . . . . . . . . . . . . . . . . . . . . . . VDD + 0.3 V
DGND to AGND . . . . . . . . . . . . . . . . . . . . . . . . VDD + 0.3 V
Digital Input Voltage to DGND . . . . . . . –0.3 V, VDD + 0.3 V
VPIN2, V PIN20 to AGND . . . . . . . . . . . . . . –0.3 V, VDD + 0.3 V
VREF A, VREF B to AGND . . . . . . . . . . . . . . . . . . . . . . . ± 25 V
VRFB A, VRFB B to AGND . . . . . . . . . . . . . . . . . . . . . . . ± 25 V
Power Dissipation (Any Package) to +75°C . . . . . . . 450 mW
Derates above +75°C by . . . . . . . . . . . . . . . . . . . 6 mW/°C
Operating Temperature Range
Commercial (J, K, L) Grades . . . . . . . . . . . –40°C to +85°C
Industrial (A, B, C) Grades . . . . . . . . . . . . –40°C to +85°C
Extended (S, T, U) Grades . . . . . . . . . . . –55°C to +125°C
Storage Temperature . . . . . . . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . . +300°C
Propagation Delay
This is a measure of the internal delays of the circuit and is
defined as the time from a digital input change to the analog
output current reaching 90% of its final value.
Channel-to-Channel Isolation
The proportion of input signal from one DAC’s reference input
which appears at the output of the other DAC, expressed as a
ratio in dB.
Digital Crosstalk
The glitch energy transferred to the output of one converter due
to a change in digital input code to the other converter. Specified in nV secs.
PIN CONFIGURATIONS
CAUTION:
2. Do not insert this device into powered sockets. Remove
power before insertion or removal.
RFB A
OUT A
AGND
OUT B
RFB B
PLCC
1. ESD sensitive device. The digital control inputs are diode
protected; however, permanent damage may occur on unconnected devices subjected to high energy electrostatic fields.
Unused devices must be stored in conductive foam or shunts.
3
2
1
20
19
PIN 1
IDENTIFIER
VREF A 4
DGND 5
AD7528
DAC A/DAC B 6
TERMINOLOGY
Relative Accuracy
TOP VIEW
(Not to Scale)
(MSB) DB7 7
Differential Nonlinearity
Differential nonlinearity is the difference between the measured
change and the ideal 1 LSB change between any two adjacent
codes. A specified differential nonlinearity of ± 1 LSB max over
the operating temperature range ensures monotonicity.
9
10
11
12
13
DB5
DB4
DB3
DB2
DB1
DB6 8
Relative accuracy or endpoint nonlinearity is a measure of the
maximum deviation from a straight line passing through the
endpoints of the DAC transfer function. It is measured after
adjusting for zero and full scale and is normally expressed in
LSBs or as a percentage of full scale reading.
18
VREF B
17
VDD
16
WR
15
CS
14
DB0 (LSB)
DIP, SOIC
OUT B
AGND 1
20
OUT A
2
19
RFB B
RFB A 3
18
VREF B
VREF A 4
17
VDD
WR
AD7528
TOP VIEW 15 CS
(Not to Scale)
14 DB0 (LSB)
(MSB) DB7 7
DGND
5
16
DAC A/DAC B 6
Gain Error
DB6 8
13
DB1
Gain error or full-scale error is a measure of the output error
between an ideal DAC and the actual device output. For the
DB5 9
12
DB2
DB4 10
11
DB3
REV. B
–3–
AD7528
INTERFACE LOGIC INFORMATION
DAC Selection:
Both DAC latches share a common 8-bit input port. The control input DAC A/DAC B selects which DAC can accept data
from the input port.
Figure 1. An inverted R-2R ladder structure is used, that is, binary weighted currents are switched between the DAC output
and AGND thus maintaining fixed currents in each ladder leg
independent of switch state.
EQUIVALENT CIRCUIT ANALYSIS
Mode Selection:
Inputs CS and WR control the operating mode of the selected
DAC. See Mode Selection Table below.
Write Mode:
When CS and WR are both low the selected DAC is in the write
mode. The input data latches of the selected DAC are transparent and its analog output responds to activity on DB0–DB7.
Hold Mode:
The selected DAC latch retains the data which was present on
DB0–DB7 just prior to CS or WR assuming a high state. Both
analog outputs remain at the values corresponding to the data in
their respective latches.
Mode Selection Table
DAC A/DAC B
CS
WR
DAC A
DAC B
L
H
X
X
L
L
H
X
L
L
X
H
WRITE
HOLD
HOLD
HOLD
HOLD
WRITE
HOLD
HOLD
Figure 2 shows an approximate equivalent circuit for one of the
AD7528’s D/A converters, in this case DAC A. A similar
equivalent circuit can be drawn for DAC B. Note that AGND
(Pin 1) is common for both DAC A and DAC B.
The current source ILEAKAGE is composed of surface and junction leakages and, as with most semiconductor devices, approximately doubles every 10°C. The resistor RO as shown in Figure
2 is the equivalent output resistance of the device which varies
with input code (excluding all 0s code) from 0.8 R to 2 R. R is
typically 11 kΩ. COUT is the capacitance due to the N-channel
switches and varies from about 50 pF to 120 pF depending
upon the digital input. g(VREF A, N) is the Thevenin equivalent
voltage generator due to the reference input voltage VREF A and
the transfer function of the R-2R ladder.
R
RFB A
OUT A
RO
g(VREF A, N)
COUT
I LKG
AGND
L = Low State; H = High State; X = Don’t Care.
Figure 2. Equivalent Analog Output Circuit of DAC A
WRITE CYCLE TIMING DIAGRAM
VDD
0
t AH
t AS
DAC A/DAC B
VDD
0
t WR
VDD
WRITE
0
t DS
VIH
VIL
DATA IN
(DB0 – DB7)
t DH
VDD
DATA IN STABLE
0
NOTES:
1. ALL INPUT SIGNAL RISE AND FALL TIMES MEASURED
FROM 10% TO 90% OF VDD.
VDD = +5V, t r = t f = 20ns;
VDD = +15V, t r = t f = 40ns;
VIH + VIL
2. TIMING MEASUREMENT REFERENCE LEVEL IS
2
The input buffers are simple CMOS inverters designed such
that when the AD7528 is operated with VDD = 5 V, the buffer
converts TTL input levels (2.4 V and 0.8 V) into CMOS logic
levels. When VIN is in the region of 2.0 volts to 3.5 volts the
input buffers operate in their linear region and pass a quiescent
current, see Figure 3. To minimize power supply currents it is
recommended that the digital input voltages be as close to the
supply rails (VDD and DGND) as is practically possible.
The AD7528 may be operated with any supply voltage in the
range 5 ≤ VDD ≤ 15 volts. With VDD = +15 V the input logic
levels are CMOS compatible only, i.e., 1.5 V and 13.5 V.
9
IDD mA (VDD = +5V)
CIRCUIT INFORMATION—D/A SECTION
The AD7528 contains two identical 8-bit multiplying D/A converters, DAC A and DAC B. Each DAC consists of a highly
stable thin film R-2R ladder and eight N-channel current steering switches. A simplified D/A circuit for DAC A is shown in
R
R
R
VREF A
2R
2R
2R
2R
S1
S2
S3
S8
VDD = +15V
800
TA = +258C
ALL DIGITAL INPUTS
TIED TOGETHER
700
8
7
600
6
500
5
4
400
300
VDD = +5V
3
200
2
100
1
IDD mA (VDD = +15V)
CHIP SELECT
CIRCUIT INFORMATION–DIGITAL SECTION
t CH
t CS
2R
0
R
RFB A
OUT A
AGND
1
2
3
4
5
6
7
8
VIN – Volts
9
10
11
12
13
14
Figure 3. Typical Plots of Supply Current, IDD vs. Logic
Input Voltage VIN, for VDD = +5 V and +15 V
DAC A DATA LATCHES
AND DRIVERS
Figure 1. Simplified Functional Circuit for DAC A
–4–
REV. B
AD7528
VIN A
(± 10V)
Table I. Unipolar Binary Code Table
R11
DAC Latch Contents
MSB
LSB
R21
VDD
DAC A/
DAC B
CS
C12
RFB A
DB0
DATA
INPUTS
DB7
INPUT
BUFFER
AGND
AD7528
10000000
C22
RFB B
LATCH
10000001
AGND
R41
CONTROL
LOGIC
WR
11111111
VOUT A
OUT A
DAC A
LATCH
OUT B
DAC B
VOUT B
01111111
DGND
AGND
00000001
R31
00000000
VIN B
(± 10V)
NOTES:
1R1, R2 AND R3, R4 USED ONLY IF GAIN ADJUSTMENT IS REQUIRED.
SEE TABLE III FOR RECOMMENDED VALUES.
2C1, C2 PHASE COMPENSATION (10pF–15pF) IS REQUIRED WHEN
USING HIGH SPEED AMPLIFIERS TO PREVENT RINGING OR OSCILLATION.
( )
Note: 1 LSB = 2−8 (V IN ) =
Analog Output
(DAC A or DAC B)
 255 
–V IN 

 256 
 129 
–V IN 

 256 
V
 128 
–V IN 
 = − IN
 256 
2
 127 
–V IN 

 256 
 1 
–V IN 

 256 
 0 
–V IN 
 =0
 256 
1
(V )
256 IN
Figure 4. Dual DAC Unipolar Binary Operation
(2 Quadrant Multiplication); See Table I
VIN A
(± 10V)
Table II. Bipolar (Offset Binary) Code Table
R5
20kV
R21
VDD
DB0
DATA
INPUTS
DB7
RFB A
INPUT
BUFFER
DAC A
LATCH
DAC Latch Contents Analog Output
MSB
LSB
(DAC A or DAC B)
R62
20kV
R11
OUT A
R72
10kV
C13
A1
A2
VOUT A
AGND
10000001
AGND
10000000
AGND
DAC A/
DAC B
CS
WR
AD7528
CONTROL
LOGIC
RFB B
LATCH
0
R41
DAC B
DGND
OUT B
AGND
R31
A3
R8
20kV
00000001
R92
10kV
R102
20kV
 1 
–V IN 

 128 
 127 
–V IN 

 128 
 128 
–V IN 

 128 
01111111
C23
VIN B
(± 10V)
A4
R12
5kV
AGND
NOTES:
1R1, R2 AND R3, R4 USED ONLY IF GAIN ADJUSTMENT IS REQUIRED.
SEE TABLE III FOR RECOMMENDED VALUES.
ADJUST R1 FOR VOUT A = 0V WITH CODE 10000000 IN DAC A LATCH.
ADJUST R3 FOR VOUT B = 0V WITH CODE 10000000 IN DAC B LATCH.
2MATCHING AND TRACKING IS ESSENTIAL FOR RESISTOR PAIRS
R6, R7 AND R9, R10.
3C1, C2 PHASE COMPENSATION (10pF–15pF) MAY BE REQUIRED
IF A1/A3 IS A HIGH SPEED AMPLIFIER.
VOUT B
00000000
( )
Note: 1 LSB = 2−7 (V IN ) =
1
(V )
128 IN
Table III. Recommended Trim Resistor
Values vs. Grade
Figure 5. Dual DAC Bipolar Operation
(4 Quadrant Multiplication); See Table II
REV. B
 127 
+V IN 

 128 
11111111
R11
5kV
–5–
Trim
Resistor
J/A/S
K/B/T
L/C/U
R1; R3
R2; R4
1k
330
500
150
200
82
AD7528
APPLICATIONS INFORMATION
Application Hints
To ensure system performance consistent with AD7528 specifications, careful attention must be given to the following points:
1. GENERAL GROUND MANAGEMENT: AC or transient
voltages between the AD7528 AGND and DGND can cause
noise injection into the analog output. The simplest method
of ensuring that voltages at AGND and DGND are equal is
to tie AGND and DGND together at the AD7528. In more
complex systems where the AGND–DGND intertie is on the
backplane, it is recommended that diodes be connected in
inverse parallel between the AD7528 AGND and DGND
pins (1N914 or equivalent).
2. OUTPUT AMPLIFIER OFFSET: CMOS DACs exhibit a
code-dependent output resistance which in turn causes a
code-dependent amplifier noise gain. The effect is a codedependent differential nonlinearity term at the amplifier
output which depends on VOS (VOS is amplifier input offset
voltage). This differential nonlinearity term adds to the R/2R
differential nonlinearity. To maintain monotonic operation, it
is recommended that amplifier VOS be no greater than 10% of
1 LSB over the temperature range of interest.
3. HIGH FREQUENCY CONSIDERATIONS: The output
capacitance of a CMOS DAC 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.
ship between input frequency and channel to channel isolation.
Figure 7 shows a printed circuit layout for the AD7528 and the
AD644 dual op amp which minimizes feedthrough and crosstalk.
SINGLE SUPPLY APPLICATIONS
The AD7528 DAC R-2R ladder termination resistors are connected to AGND within the device. This arrangement is particularly convenient for single supply operation because AGND
may be biased at any voltage between DGND and VDD. Figure
8 shows a circuit which provides two +5 V to +8 V analog outputs by biasing AGND +5 V up from DGND. The two DAC
reference inputs are tied together and a reference input voltage
is obtained without a buffer amplifier by making use of the
constant and matched impedances of the DAC A and DAC B
reference inputs. Current flows through the two DAC R-2R
ladders into R1 and R1 is adjusted until the VREF A and VREF B
inputs are at +2 V. The two analog output voltages range from
+5 V to +8 V for DAC codes 00000000 to 11111111.
VDD = +15V
DAC A
VOUT A = +5V TO +8V
DB0
DATA
INPUTS
DB7
CS
WR
SUGGESTED
OP AMP:
AD644
AD7528
DAC A/DAC B
VOUT B = +5V TO +8V
DAC B
2 VOLTS
R1
10kV
AD584J
R2
1kV
DYNAMIC PERFORMANCE
GND
The dynamic performance of the two DACs in the AD7528 will
depend upon the gain and phase characteristics of the output
amplifiers together with the optimum choice of the PC board
layout and decoupling components. Figure 6 shows the relation
–100
TA = +258C
VDD = +15V
VIN = 20V PEAK TO PEAK
ISOLATION – dB
–90
VDD
–80
Figure 8. AD7528 Single Supply Operation
Figure 9 shows DAC A of the AD7528 connected in a positive
reference, voltage switching mode. This configuration is useful
in that VOUT is the same polarity as VIN allowing single supply
operation. However, to retain specified linearity, VIN must be in
the range 0 V to +2.5 V and the output buffered or loaded with
a high impedance, see Figure 10. Note that the input voltage is
connected to the DAC OUT A and the output voltage is taken
from the DAC VREF A pin.
–70
VOUT
VIN (0V TO +2.5V)
VREF A
–60
–50
VDD
+15V
20k
50k
100k
200k
INPUT FREQUENCY – Hz
500k
DAC A
OUT A
AD7528
1M
Figure 9. AD7528 in Single Supply, Voltage Switching Mode
Figure 6. Channel-to-Channel Isolation
3
V+
PIN 8 OF TO-5 CAN (AD644)
TA = +258C
VDD = +15V
ERROR – LSB
AD644
V–
AGND
AD7528 PIN 1
C1 LOCATION
VREF B*
VDD
WR
CS
LSB
AD7528
C2 LOCATION *NOTE
INPUT SCREENS
TO REDUCE
VREF A*
FEEDTHROUGH.
DGND
LAYOUT SHOWS
DAC A/DAC B
COPPER SIDE
(i.e., BOTTOM VIEW).
MSB
2
NONLINEARITY
1
DIFFERENTIAL
NONLINEARITY
2.5
Figure 7. Suggested PC Board Layout for AD7528 with
AD644 Dual Op Amp
3
3.5
4
5
4.5
5.5
VIN A – Volts
6
6.5
7
7.5
Figure 10. Typical AD7528 Performance in Single Supply
Voltage Switching Mode (K/B/T, L/C/U Grades)
–6–
REV. B
AD7528
MICROPROCESSOR INTERFACE
ADDRESS BUS
A8–A15
A**
ADDRESS BUS
A0–A15
A**
VMA
CPU
6800
DAC A/DAC B
ADDRESS
DECODE
LOGIC
D0–D7
CS
DAC A
WR
AD7528*
DB0
DB7
DAC B
A + 1**
WR
CS
DAC A
WR
AD7528*
DB0
DB7
DAC B
A + 1**
f2
DAC A/DAC B
ADDRESS
DECODE
LOGIC
CPU
8085
LATCH
8212
ALE
ADDR/DATA BUS
AD0–AD7
*ANALOG CIRCUITRY HAS BEEN OMITTED FOR CLARITY
**A = DECODED 7528 ADDR DAC A
A + 1 = DECODED 7528 ADDR DAC B
NOTE:
8085 INSTRUCTION SHLD (STORE H & L DIRECT) CAN UPDATE
BOTH DACs WITH DATA FROM H AND L REGISTERS
DATA BUS
*ANALOG CIRCUITRY HAS BEEN OMITTED FOR CLARITY
**A = DECODED 7528 ADDR DAC A
A + 1 = DECODED 7528 ADDR DAC B
Figure 11. AD7528 Dual DAC to 6800 CPU Interface
Figure 12. AD7528 Dual DAC to 8085 CPU Interface
PROGRAMMABLE WINDOW COMPARATOR
VCC
RFB A
OUT A 3
VREF A
DAC A
2
DB0
DATA
INPUTS
DB7
CS
1kV
7
AD311
COMPARATOR
AD7528
WR
OUT B 2
DAC A/DAC B
+VREF
In the circuit of Figure 13 the AD7528 is used to implement a
programmable window comparator. DACs A and B are loaded
with the required upper and lower voltage limits for the test,
respectively. If the test input is not within the programmed
limits, the pass/fail output will indicate a fail (logic zero).
VDD
TEST INPUT
0 TO –VREF
3
DAC B
VREF B
RFB B
PASS/ FAIL
OUTPUT
7
AD311
COMPARATOR
Figure 13. Digitally Programmable Window Comparator
(Upper and Lower Limit Detector)
PROGRAMMABLE STATE VARIABLE FILTER
In this state variable or universal filter configuration (Figure 14)
DACs A1 and B1 control the gain and Q of the filter characteristic while DACs A2 and B2 control the cutoff frequency, fC .
DACs A2 and B2 must track accurately for the simple expression for fC to hold. This is readily accomplished by the AD7528.
Op amps are 2 × AD644. C3 compensates for the effects of op
amp gain bandwidth limitations.
The filter provides low pass, high pass and band pass outputs
and is ideally suited for applications where microprocessor
control of filter parameters is required, e.g., equalizer, tone
controls, etc.
Programmable range for component values shown is fC = 0 kHz
to 15 kHz and Q = 0.3 to 4.5.
CIRCUIT EQUATIONS
R5
30kV
R3
10kV
A1
VDD
R4
30kV
A2
C3
47pF
HIGH
PASS
OUTPUT
C1
1000pF
C2
1000pF
A3
A4
BAND
PASS
OUTPUT
VDD
AD7528
VIN
DAC A1
RS
DAC B1
RF
DB0–DB7
DATA 1
DAC A2
R1
AD7528
DAC B2
R2
DB0–DB7
CS WR DAC A/DAC B
DATA 2
CS WR DAC A/DAC B
Figure 14. Digitally Controlled State Variable Filter
REV. B
–7–
C1 = C 2, R1 = R2, R4 = R5
LOW
PASS
OUTPUT
1
2 π R1C1
R3 RF
Q=
×
R4 RFBB1
RF
AO = –
RS
fC =
NOTE
DAC Equivalent Resistance
Equals
256 × ( DAC Ladder Resistance )
DAC Digital Code
AD7528
In this configuration the AD7528 functions as a 2-channel digitally controlled attenuator. Ideal for stereo audio and telephone
signal level control applications. Table IV gives input codes vs.
attenuation for a 0 dB to 15.5 dB range.
 Attenuation, dB

20


Input Code = 256 ⫻ 10 exp  −
VDD
VIN A
DAC A
A1
DB0
DATA BUS
DB7
CS
AD7528
WR
DAC A/DAC B
VIN B
DAC B
A2
VOUT B
VOUT A
SUGGESTED
OP AMP: AD644
Figure 15. Digitally Controlled Dual Telephone Attenuator
Table IV. Attenuation vs. DAC A, DAC B Code for the Circuit
of Figure 15
Attn. DAC Input
dB
Code
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
Code In
Decimal
11111111
11110010
11100100
11010111
11001011
11000000
10110101
10101011
10100010
10011000
10010000
10001000
10000000
01111001
01110010
01101100
Attn. DAC Input
dB
Code
255
242
228
215
203
192
181
171
162
152
144
136
128
121
114
108
88.0
88.5
89.0
89.5
10.0
10.5
11.0
11.5
12.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
Code In
Decimal
01100110
01100000
01011011
01010110
01010001
01001100
01001000
01000100
01000000
00111101
00111001
00110110
00110011
00110000
00101110
00101011
102
96
91
86
81
76
72
68
64
61
57
54
51
48
46
43
C681e–0–9/98
DIGITALLY CONTROLLED DUAL TELEPHONE
ATTENUATOR
For further applications information the reader is referred to
Analog Devices Application Note on the AD7528.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
20-Lead Cerdip (Q-20)
20-Lead Plastic DIP (N-20)
1.07 (27.18) MAX
11
0.28 (7.11)
0.24 (6.1)
PIN 1
1
20
10
11
1
0.32 (8.128)
0.29 (7.366)
0.97 (24.64)
0.935 (23.75)
0.20 (5.0)
0.14 (3.56)
0.14 (3.56)
0.125 (3.17)
0.15 (3.8)
0.125 (3.18)
SEATING
PLANE
10
PIN 1
SEATING
0.011 (0.28)
0.11 (2.79) 0.065 (1.66) PLANE
0.021 (0.533)
158
0.009 (0.23)
0.09
(2.28)
0.045
(1.15)
08
0.015 (0.381)
LEAD NO. 1 IDENTIFIED BY DOT OR NOTCH
LEADS ARE SOLDER OR TIN-PLATED KOVAR OR ALLOY 42
0.011 (0.28)
0.009 (0.23)
20-Lead SOIC (R-20)
20-Lead Plastic Leaded Chip Carrier (P-20A)
0.5118 (13.00)
0.4961 (12.60)
20
11
10
0.048 (1.21)
0.042 (1.07)
0.4193 (10.65)
0.3937 (10.00)
3
4
18
TOP VIEW
0.0118 (0.30)
0.0040 (0.10)
0.1043 (2.65)
0.0926 (2.35)
8
0.02
9
(0.51)
MAX
0.02 (0.51)
MAX
0.0291 (0.74)
3 458
0.0098 (0.25)
88
0.0500 0.0192 (0.49) SEATING
08
(1.27) 0.0138 (0.35) PLANE 0.0125 (0.32)
BSC
0.0091 (0.23)
0.12 (3.05)
0.09 (2.29)
0.020 (0.51) MIN
19
PIN 1
IDENTIFIER
(PINS DOWN)
PIN 1
0.180 (4.47)
0.165 (4.19)
0.395 (10.02)
SQ
0.385 (9.78)
0.356 (9.04)
0.350 (8.89) SQ
0.2992 (7.60)
0.2914 (7.40)
1
0.32 (8.128)
0.30 (7.62)
0.135 (3.429)
0.125 (3.17)
0.145 (3.683)
MIN
0.125 (3.175)
MIN
0.07 (1.78) 0.02 (0.5) 0.11 (2.79)
158
0.05 (1.27) 0.016 (0.41) 0.09 (2.28)
08
LEAD NO. 1 IDENTIFIED BY DOT OR NOTCH
LEADS ARE SOLDER OR TIN-PLATED KOVAR OR ALLOY 42
0.255 (6.477)
0.245 (6.223)
0.021 (0.53)
0.013 (0.33)
0.050
(1.27)
BSC
0.032 (0.81)
0.026 (0.66)
14
13
0.025 (0.64)
MIN
0.060 (1.53)
MIN
0.0500 (1.27)
0.0157 (0.40)
–8–
REV. B
PRINTED IN U.S.A.
20
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