LC2MOS
16-Bit Voltage Output DAC
AD7846
Rev. G
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FEATURES
16-bit monotonicity over temperature
±2 LSBs integral linearity error
Microprocessor compatible with readback capability
Unipolar or bipolar output
Multiplying capability
Low power (100 mW typical)
FUNCTIONAL BLOCK DIAGRAM
A2
A1
A3
16
SEGMENT
SWITCH
MATRIX
R
R
R
12-BIT DAC
DAC LATCH
I/O LATCH
CONTROL
LOGIC
AD7846
R
21 4
7
8
9
6
5
23
22
25
24
R
V
REF–
V
REF+
V
SS
DGND
CLR
LDAC
R/W
CS
V
OUT
R
IN
V
DD
V
CC
412
12
DB15 DB0
08490-001
10 3 20
Figure 1.
GENERAL DESCRIPTION
The AD7846 is a 16-bit DAC constructed with the Analog Devices,
Inc., LC2MOS process. It has VREF+ and VREF− reference inputs
and an on-chip output amplifier. These can be configured to
give a unipolar output range (0 V to +5 V, 0 V to +10 V) or
bipolar output ranges (±5 V, ±10 V).
The DAC uses a segmented architecture. The four MSBs in the
DAC latch select one of the segments in a 16-resistor string.
Both taps of the segment are buffered by amplifiers and fed to a
12-bit DAC, which provides a further 12 bits of resolution. This
architecture ensures 16-bit monotonicity. Excellent integral
linearity results from tight matching between the input offset
voltages of the two buffer amplifiers.
In addition to the excellent accuracy specifications, the AD7846
also offers a comprehensive microprocessor interface. There are
16 data I/O pins, plus control lines (CS, R/W, LDAC and CLR).
R/W and CS allow writing to and reading from the I/O latch.
This is the readback function, which is useful in ATE applications.
LDAC allows simultaneous updating of DACs in a multi-DAC
system and the CLR line will reset the contents of the DAC latch
to 00…000 or 10…000 depending on the state of R/W. This
means that the DAC output can be reset to 0 V in both the
unipolar and bipolar configurations.
The AD7846 is available in 28-lead plastic, ceramic, and PLCC
packages.
PRODUCT HIGHLIGHTS
1. 16-Bit Monotonicity
The guaranteed 16-bit monotonicity over temperature
makes the AD7846 ideal for closed-loop applications.
2. Readback
The ability to read back the DAC register contents
minimizes software routines when the AD7846 is used in
ATE systems.
3. Power Dissipation
Power dissipation of 100 mW makes the AD7846 the
lowest power, high accuracy DAC on the market.
AD7846
Rev. G | Page 2 of 24
TABLE OF CONTENTS
Features .............................................................................................. 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Product Highlights ........................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
AC Performance Characteristics ................................................ 4
Timing Characteristics ................................................................ 5
Absolute Maximum Ratings ............................................................ 6
ESD Caution .................................................................................. 6
Pin Configurations and Function Descriptions ........................... 7
Typical Performance Characteristics ............................................. 8
Terminology .................................................................................... 10
Circuit Description ......................................................................... 11
Digital Section ............................................................................. 11
Digital-to-Analog Conversion .................................................. 11
Output Stage ................................................................................ 12
Unipolar Binary Operation ........................................................... 13
Bipolar Operation ........................................................................... 14
Multiplying Operation ............................................................... 14
Position Measurement Application .............................................. 15
Microprocessor Interfacing ........................................................... 16
AD7846-to-8086 Interface ........................................................ 16
AD7846-to-MC68000 Interface ............................................... 16
Digital Feedthrough ....................................................................... 17
Application Hints ........................................................................... 18
Noise ............................................................................................ 18
Grounding ................................................................................... 18
Printed Circuit Board Layout ................................................... 18
Outline Dimensions ....................................................................... 20
Ordering Guide .......................................................................... 22
REVISION HISTORY
4/10—Rev. F to Rev. G
Change to Figure 1 ........................................................................... 1
12/09—Rev. E to Rev. F
Updated Format .................................................................. Universal
Changes to Table 4 ............................................................................ 6
Deleted Other Output Voltage Ranges Section ............................ 9
Deleted Figure 20 and Table 5; Renumbered Sequentially ......... 9
Deleted Test Application Section and Figure 21 ........................ 10
Deleted Figure 29 to Figure 31 ...................................................... 14
Changes to Printed Circuit Board Layout Section ..................... 18
Updated Outline Dimensions ....................................................... 20
Changes to Ordering Guide .......................................................... 22
AD7846
Rev. G | Page 3 of 24
SPECIFICATIONS
VDD = +14.25 V to +15.75 V; VSS = −14.25 V to –15.75 V; VCC = +4.75 V to +5.25 V. VOUT loaded with 2 kΩ, 1000 pF to 0 V; VREF+ = +5 V;
RIN connected to 0 V. All specifications TMIN to TMAX, unless otherwise noted.
Table 1.
Parameter1 J, A Versions K, B Versions Unit Test Conditions/Comments
RESOLUTION 16 16 Bits
UNIPOLAR OUTPUT VREF− = 0 V, VOUT = 0 V to +10 V
Relative Accuracy at +25°C ±12 ±4 LSB typ 1 LSB = 153 V
TMIN to TMAX ±16 ±8 LSB max
Differential Nonlinearity Error ±1 ±0.5 LSB max All grades guaranteed monotonic
Gain Error at +25°C ±12 ±6 LSB typ VOUT load = 10 MΩ
TMIN to TMAX ±16 ±16 LSB max
Offset Error at +25°C ±12 ±6 LSB typ
TMIN to TMAX ±16 ±16 LSB max
Gain TC2 ±1 ±1 ppm FSR/°C typ
Offset TC2 ±1 ±1 ppm FSR/°C typ
BIPOLAR OUTPUT VREF− = –5 V, VOUT = −10 V to +10 V
Relative Accuracy at +25°C ±6 ±2 LSB typ 1 LSB = 305 V
TMIN to TMAX ±8 ±4 LSB max
Differential Nonlinearity Error ±1 ±0.5 LSB max All grades guaranteed monotonic
Gain Error at +25°C ±6 ±4 LSB typ VOUT load = 10 MΩ
TMIN to TMAX ±16 ±16 LSB max
Offset Error at +25°C ±6 ±4 LSB typ VOUT load = 10 MΩ
TMIN to TMAX ±16 ±12 LSB max
Bipolar Zero Error at +25°C ±6 ±4 LSB typ
TMIN to TMAX ±12 ±8 LSB max
Gain TC2 ±1 ±1 ppm FSR/°Ctyp
Offset TC2 ±1 ±1 ppm FSR/°Ctyp
Bipolar Zero TC2 ±1 ±1 ppm FSR/°Ctyp
REFERENCE INPUT
Input Resistance 20 20 kΩ min Resistance from VREF+ to VREF−
40 40 kΩ max Typically 30 kΩ
VREF+ Range VSS + 6 to VSS + 6 to V min to
V
DD − 6 VDD − 6 V max
VREF− Range VSS + 6 to VSS + 6 to V min to
V
DD − 6 VDD − 6 V max
OUTPUT CHARACTERISTICS
Output Voltage Swing VSS + 4 to VSS + 4 to V max
VDD − 3 VDD − 3
Resistive Load 2 2 kΩ min To 0 V
Capacitive Load 1000 1000 pF max To 0 V
Output Resistance 0.3 0.3 Ω typ
Short Circuit Current ±25 ±25 mA typ To 0 V or any power supply
DIGITAL INPUTS
VIH (Input High Voltage) 2.4 2.4 V min
VIL (Input Low Voltage) 0.8 0.8 V max
IIN (Input Current) ±10 ±10 A max
CIN (Input Capacitance)2 10 10 pF max
AD7846
Rev. G | Page 4 of 24
Parameter1 J, A Versions K, B Versions Unit Test Conditions/Comments
DIGITAL OUTPUTS
VOL (Output Low Voltage) 0.4 0.4 V max ISINK = 1.6 mA
VOH (Output High Voltage) 4.0 4.0 V min ISOURCE = 400 A
Floating State Leakage Current ±10 ±10 A max DB0 to DB15 = 0 to VCC
Floating State Output Capacitance2 10 10 pF max
POWER REQUIREMENTS3
VDD +11.4/+15.75 +11.4/+15.75 V min/V max
VSS −11.4/−15.75 −11.4/−15.75 V min/V max
VCC +4.75/+5.25 +4.75/+5.25 V min/V max
IDD 5 5 mA max VOUT unloaded
ISS 5 5 mA max VOUT unloaded
ICC 1 1 mA max
Power Supply Sensitivity4 1.5 1.5 LSB/V max
Power Dissipation 100 100 mW typ VOUT unloaded
1 Temperature ranges as follows: J, K versions: 0°C to +70°C; A, B versions: −40°C to +85°C.
2 Guaranteed by design and characterization, not production tested.
3 The AD7846 is functional with power supplies of ±12 V. See the Typical Performance Characteristics section.
4 Sensitivity of gain error, offset error, and bipolar zero error to VDD, VSS variations.
AC PERFORMANCE CHARACTERISTICS
These characteristics are included for design guidance and are not subject to test. VREF+ = +5 V; VDD = +14.25 V to +15.75 V; VSS = −14.25 V
to −15.75 V; VCC = +4.75 V to +5.25 V; RIN connected to 0 V, unless otherwise noted.
Table 2.
Parameter Limit at TMIN to TMAX (All Versions) Unit Test Conditions/Comments
Output Settling Time1 6 s max To 0.006% FSR, VOUT loaded, VREF− = 0 V, typically 3.5 s
9 s max To 0.003% FSR, VOUT loaded, VREF− = –5 V, typically 6.5 s
Slew Rate 7 V/s typ
Digital-to-Analog Glitch
Impulse 70 nV-sec typ DAC alternately loaded with 10…0000 and 01…1111,
VOUT unloaded
AC Feedthrough 0.5 mV p-p typ VREF− = 0 V, VREF+ = 1 V rms, 10 kHz sine wave, DAC loaded
with all 0s
Digital Feedthrough 10 nV-sec typ DAC alternately loaded with all 1s and all 0s. CS high
Output Noise Voltage
Density, 1 kHz to 100 kHz
50 nV/√Hz typ Measured at VOUT, DAC loaded with 0111011…11,
VREF+ = VREF− = 0 V
1 LDAC = 0. Settling time does not include deglitching time of 2.5 µs (typ).
AD7846
Rev. G | Page 5 of 24
TIMING CHARACTERISTICS
VDD = +14.25 V to +15.75 V, VSS = −14.25 V to −15.75 V, VCC = +4.75 V to +5.25 V, unless otherwise noted.
Table 3.
Parameter1 Limit at TMIN to TMAX (All Versions) Unit Test Conditions/Comments
t1 0 ns min R/W to CS setup time
t2 60 ns min CS pulse width (write cycle)
t3 0 ns min R/W to CS hold time
t4 60 ns min Data setup time
t5 0 ns min Data hold time
t62 120 ns max Data access time
t73 10 ns min Bus relinquish time
60 ns max
t8 0 ns min CLR setup time
t9 70 ns min CLR pulse width
t10 0 ns min CLR hold time
t11 70 ns min LDAC pulse width
t12 130 ns min CS pulse width (read cycle)
1 Timing specifications are sample tested at +25°C to ensure compliance. All input control 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 t6 is measured with the load circuits of Figure 3 and Figure 4 and defined as the time required for an output to cross 0.8 V or 2.4 V.
3 t7 is defined as the time required for an output to change 0.5 V when loaded with the circuits of Figure 5 and Figure 6.
DB0
TO
DB15
5V
t
3
t
1
t
3
DATA VALIDDATA VALID
t
11
t
10
LDAC
CLR
CS
R/W 0V
5V
0V
5V
0V
5V
0V
5V
0V
t
10
t
8
t
9
t
6
t
1
t
8
t
9
t
4
t
5
t
7
t
12
t
2
0
8490-006
Figure 2. Timing Diagram
DBn
3kΩ100pF
DGND
0
8490-002
Figure 3. Load Circuit for Access Time (t6)—High Z to VOH
DBn
100pF
3kΩ
DGND
5
V
08490-003
Figure 4. Load Circuits for Bus Relinquish Time (t6)—High Z to VOL
DBn
3kΩ10pF
DGND
08490-004
Figure 5. Load Circuit for Access Time (t7)—High Z to VOH
DBn
10pF
3kΩ
DGND
5
V
08490-005
Figure 6. Load Circuits for Bus Relinquish Time (t7)—High Z to VOL
AD7846
Rev. G | Page 6 of 24
ABSOLUTE MAXIMUM RATINGS
Table 4.
Parameter Rating
VDD to DGND −0.4 V to +17 V
VCC to DGND −0.4 V, VDD + 0.4 V, or +7 V
(whichever is lower)
VSS to DGND +0.4 V to −17 V
VREF+ to DGND VDD + 0.4 V, VSS − 0.4 V
VREF− to DGND VDD + 0.4 V, VSS − 0.4 V
VOUT to DGND1 V
DD + 0.4 V, VSS − 0.4 V, or ±10 V
(whichever is lower)
RIN to DGND VDD + 0.4 V, VSS − 0.4 V
Digital Input Voltage to DGND −0.4 V to VCC + 0.4 V
Digital Output Voltage to DGND −0.4 V to VCC + 0.4 V
Power Dissipation (Any Package)
To +75°C 1000 mW
Derates above +75°C 10 mW/°C
Operating Temperature Range
J, K Versions 0°C to +70°C
A, B Versions −40°C to +85°C
Storage Temperature Range −65°C to +150°C
Lead Temperature (Soldering) +300°C
1 VOUT can be shorted to DGND, VDD, VSS, or VCC provided that the power
dissipation of the package is not exceeded.
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
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
AD7846
Rev. G | Page 7 of 24
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
TOP VIEW
(Not to Scale)
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
AD7846
DB11
DB12
DB13
DB14
DB15
DB2
DB1
DB0
VDD
VCC
VSS
VOUT
V
REF+
V
REF–
RIN
DB10
DB9
DB8
DB7
DB6
DGND
DB3
DB4
DB5
LDAC
R/W
CS
CLR
08490-007
Figure 7. PDIP Pin Configuration
25
24
23
22
21
20
19
5
6
7
8
9
10
11
4 3 2 1 28 27 26
PIN 1
IDENTIFIER
TOP VIEW
(Not to Scale)
12 13 14 15 16 17 18
LDAC
CLR
CS
R/W
DGND
DB6
V
OUT
V
REF+
V
REF–
R
IN
V
SS
DB15
DB14
V
DD
DB0
DB1
DB2
DB3
DB4
DB5
DB13
DB12
DB11
DB10
DB9
DB8
DB7
AD7846
V
CC
08490-008
Figure 8. CERDIP Pin Configuration
Table 5. Pin Function Descriptions
Pin Mnemonic Description
1 to 3 DB2 to DB0 Data I/Os. DB0 is LSB.
4 VDD Positive Supply for Analog Circuitry. This is +15 V nominal.
5 VOUT DAC Output Voltage.
6 RIN Input to Summing Resistor of DAC Output Amplifier. This is used to select output voltage ranges. See Table 6.
7 VREF+ V
REF+ Input. The DAC is specified for VREF+ = +5 V.
8 VREF− VREF− Input. For unipolar operation connect VREF− to 0 V, and for bipolar operation connect it to −5 V. The device is
specified for both conditions.
9 VSS Negative Supply for the Analog Circuitry. This is −15 V nominal.
10 to 19 DB15 to DB6 Data I/Os. DB15 is MSB.
20 DGND Ground for Digital Circuitry.
21 VCC Positive Supply for Digital Circuitry. This is +5 V nominal.
22 R/W R/W Input. This pin can be used to load data to the DAC or to read back the DAC latch contents.
23 CS Chip Select Input. This pin selects the device.
24 CLR Clear Input. The DAC can be cleared to 000…000 or 100…000. See Table 7.
25 LDAC Asynchronous Load Input to DAC.
26 to 28 DB5 to DB3 Data I/Os.
Table 6. Output Voltage Ranges
Output Range VREF+ VREF− R
IN
0 V to +5 V +5 V 0 V VOUT
0 V to +10 V +5 V 0 V 0 V
+5 V to −5 V +5 V −5 V VOUT
+5 V to −5 V +5 V 0 V +5 V
+10 V to −10 V +5 V −5 V 0 V
AD7846
Rev. G | Page 8 of 24
TYPICAL PERFORMANCE CHARACTERISTICS
1V 2mV 20µs
–0.40VA1
08490-009
Figure 9. AC Feedthrough, VREF+ = 1 V rms, 10 kHz Sine Wave
FREQUENCY (Hz)
V
OUT
(mV p-p)
0
100
2
1k 10k 100k 1M
4
6
1
3
5
7
8
V
DD
= +15V
V
SS
= –15V
V
REF+
= +1V rms
V
REF–
= 0V
08490-010
Figure 10. AC Feedthrough to VOUT vs. Frequency
FREQUENCY (Hz)
30
010 100 1k 10k 100k 1M 10M
20
10
5
25
15
V
OUT
(V p-p)
V
DD
= +15V
V
SS
= –15V
V
REF+
= ±5V SINE WAVE
V
REF–
= 0V
GAIN = +2
08490-011
Figure 11. Large Signal Frequency Response
FREQUENCY (Hz)
NOISE SPECTRAL DENSITY (nV/√Hz)
0
100
100 1k 10k 100k 1M
200
300
400
50
150
250
350
450
500
V
REF+
= V
REF–
= 0V
GAIN = +1
DAC LOADED WITH ALL 1s
08490-012
Figure 12. Noise Spectral Density
50mV/DIV
5V/DIV
0.5µs/DIV
DATA
V
OUT
0
8490-013
Figure 13. Digital-to-Analog Glitch Impulse Without Internal Deglitcher
(10…000 to 011…111 Transition)
50mV/DIV
5V/DIV
DATA
5V/DIV
LDAC
1µs/DIV
V
OUT
0
8490-014
Figure 14. Digital-to-Analog Glitch Impulse with Internal Deglitcher
(10…000 to 011…111 Transition)
AD7846
Rev. G | Page 9 of 24
10V 5V 2µs
0VA1
VREF+, ±5V
VOUT+, ±10V
08490-015
Figure 15. Pulse Response (Large Signal)
1µs
0.025VA1
100mV 50mV
VREF+, ±50mV
VOUT+, ±100mV
08490-016
Figure 16. Pulse Response (Small Signal)
START 100.0Hz
RBW 3Hz
REF 2.24V
10dB/DIV
MARKER 442.0Hz
1.70V
STOP 2000.0Hz
ST 422 SEC
RANGE 3.98V
VBW 10Hz
08490-017
Figure 17. Spectral Response of Digitally Constructed Sine Wave
VDD, VSS (V)
INL (LSB)
0.5
11 12 13 14 15
1.0
1.5
2.0
2.5
3.0
3.5
4.0
16
TA = +25°C
VREF+ = +5V
VREF– = 0V
GAIN = +1
0
8490-018
Figure 18. Typical Integral Nonlinearity vs. VDD/VSS
VDD, VSS (V)
DNL (LSB)
0
11 12 13 14 15
0.1
0.3
0.2
0.4
0.5
0.7
0.6
0.9
0.8
1.0
16
TA = +25°C
VREF+ = +5V
VREF– = 0V
GAIN = +1
0
8490-019
Figure 19. Typical Differential Nonlinearity vs. VDD/VSS
AD7846
Rev. G | Page 10 of 24
TERMINOLOGY
Least Significant Bit
This is the analog weighting of 1 bit of the digital word in a
DAC. For the AD7846, 1 LSB = (VREF+ − VREF−)/216.
Relative Accuracy
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 both endpoints (that is, offset and gain errors are
adjusted out) and is normally expressed in least significant bits
or as a percentage of full-scale range.
Differential Nonlinearity
Differential nonlinearity is the difference between the measured
change and the ideal change between any two adjacent codes. A
specified differential nonlinearity of ±1 LSB over the operating
temperature range ensures monotonicity.
Gain Error
Gain error is a measure of the output error between an ideal
DAC and the actual device output with all 1s loaded after offset
error has been adjusted out. Gain error is adjustable to zero
with an external potentiometer.
Offset Error
This is the error present at the device output with all 0s loaded
in the DAC. It is due to op amp input offset voltage and bias
current and the DAC leakage current.
Bipolar Zero Error
When the AD7846 is connected for bipolar output and 10…000
is loaded to the DAC, the deviation of the analog output from
the ideal midscale of 0 V is called the bipolar zero error.
Digital-to-Analog Glitch Impulse
This is 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-sec or nV-sec
depending upon whether the glitch is measured as a current or
a voltage.
Multiplying Feedthrough Error
This is an ac error due to capacitive feedthrough from either of
the VREF terminals to VOUT when the DAC is loaded with all 0s.
Digital Feedthrough
When the DAC is not selected (that is, CS is held high), high
frequency logic activity on the digital inputs is capacitively
coupled through the device to show up as noise on the VOUT pin.
This noise is digital feedthrough.
AD7846
Rev. G | Page 11 of 24
CIRCUIT DESCRIPTION
DIGITAL SECTION
Figure 20 shows the digital control logic and on-chip data latches
in the AD7846. Table 7 is the associated truth table. The digital-
to-analog converter (DAC) has two latches that are controlled
by four signals: CS, R/W, LDAC, and CLR. The input latch is
connected to the data bus (DB15 to DB0). A word is written to
the input latch by bringing CS low and R/W low. The contents
of the input latch can be read back by bringing CS low and R/W
high. This feature is called readback and is used in system
diagnostic and calibration routines.
Data is transferred from the input latch to the DAC latch with
the LDAC strobe. The equivalent analog value of the DAC latch
contents appears at the DAC output. The CLR pin resets the
DAC latch contents to 000…000 or 100…000, depending on the
state of R/W. Writing a CLR loads 000…000 and reading a CLR
loads 100…000. To reset a DAC to 0 V in a unipolar system, the
user should assert CLR while R/W is low; to reset to 0 V in a
bipolar system, assert the CLR while R/W is high.
R/W
CLR
CS
DB15 DB0
16
16
16
DAC
DB15 RST
DB15 SET
DB14 TO DB0
RST
3-STATE I/O
LATCH
DB15 TO DB0
LATCHES
LDAC
08490-020
Figure 20. Input Control Logic
Table 7. Control Logic Truth Table
CS R/W LDAC CLR Function
1 X X X 3-state DAC I/O latch in high-Z state
0 0 X X DAC I/O latch loaded with DB15
to DB0
0 1 X X Contents of DAC I/O latch available
on DB15 to DB0
X X 0 1 Contents of DAC I/O latch transferred
to DAC latch
X 0 X 0 DAC latch loaded with 000…000
X 1 X 0 DAC latch loaded with 100…000
DIGITAL-TO-ANALOG CONVERSION
Figure 21 shows the digital-to-analog section of the AD7846.
There are three DACs, each of which has its own buffer
amplifiers. DAC1 and DAC2 are 4-bit DACs. They share a
16-resistor string but have their own analog multiplexers. The
voltage reference is applied to the resistor string. DAC3 is a
12-bit voltage mode DAC with its own output stage.
The four MSBs of the 16-bit digital code drive DAC1 and DAC2,
and the 12 LSBs control DAC3. Using DAC1 and DAC2, the
MSBs select a pair of adjacent nodes on the resistor string and
present that voltage to the positive and negative inputs of
DAC3. This DAC interpolates between these two voltages to
produce the analog output voltage.
To prevent nonmonotonicity in the DAC due to amplifier offset
voltages, DAC1 and DAC2 leap along the resistor string. For
example, when switching from Segment 1 to Segment 2, DAC1
switches from the bottom of Segment 1 to the top of Segment 2
while DAC2 stays connected to the top of Segment 1. The code
driving DAC3 is automatically complemented to compensate
for the inversion of its inputs. This means that any linearity
effects due to amplifier offset voltages remain unchanged when
switching from one segment to the next and 16-bit monotonicity is
ensured if DAC3 is monotonic. Thus, 12-bit resistor matching
in DAC3 guarantees overall 16-bit monotonicity. This is much
more achievable than 16-bit matching, which a conventional
R-2R structure needs.
AD7846
Rev. G | Page 12 of 24
S1
V
REF+
V
REF–
DAC1
SEGMENT 1
SEGMENT 16
S3
S15
S17 S16
S14
S4
S2
DAC2
DAC3
12-BIT DAC
DB11 TO DB0
DB15 TO DB12 DB15 TO DB12
R
R
V
OUT
R
IN
A3
A2
A1
08490-021
Figure 21. Digital-to-Analog Conversion
OUTPUT STAGE
The output stage of the AD7846 is shown in Figure 22. It is capable
of driving a 2 kΩ/1000 pF load. It also has a resistor feedback
network that allows the user to configure it for gains of 1 or 2.
Table 6 shows the different output ranges that are possible.
An additional feature is that the output buffer is configured as a
track-and-hold amplifier. Although normally tracking its input,
this amplifier is placed in a hold mode for approximately 2.5 µs
after the leading edge of LDAC. This short state keeps the DAC
output at its previous voltage while the AD7846 is internally
changing to its new value. Thus, any glitches that occur in the
transition are not seen at the output. In systems where the
LDAC is tied permanently low, the deglitching is not in
operation. and show the outputs of the
AD7846 without and with the deglitcher.
Figure 13 Figure 14
C1
LDAC
V
OUT
R
IN
DAC3
ONE
SHOT
10kΩ
10kΩ
08490-022
Figure 22. Output Stage
AD7846
Rev. G | Page 13 of 24
UNIPOLAR BINARY OPERATION
Figure 23 shows the AD7846 in the unipolar binary circuit
configuration. The DAC is driven by the AD586 +5 V reference.
Because RIN is tied to 0 V, the output amplifier has a gain of 2
and the output range is 0 V to +10 V. If a 0 V to +5 V range is
required, RIN should be tied to VOUT, configuring the output
stage for a gain of 1. Table 8 gives the code table for the circuit
of Figure 23.
R
IN
V
OUT
DGND
+15
V
+5
V
V
CC
V
DD
V
REF+
V
REF–
R1
10kΩ
C1
1µF
SIGNAL
GROUND
–15V
*ADDITIONAL PINS
OMITTED FOR CLARITY
AD7846*
AD586
V
OUT
(0V TO +10V)
V
SS
2
5
4
67
21
5
20
6
4
8
8
08490-023
Figure 23. Unipolar Binary Operation
Table 8. Code Table for Figure 23
Binary Number in DAC Latch
MSB LSB1 Analog Output (VOUT)
1111 1111 1111 1111 +10 (65,535/65,536) V
1000 0000 0000 0000 +10 (32,768/65,536) V
0000 0000 0000 0001 +10 (1/65,536) V
0000 0000 0000 0000 0 V
1 LSB = 10 V/216 = 10 V/65,536 = 152 µV.
Offset and gain can be adjusted in Figure 23 as follows:
• To adjust offset, disconnect the VREF− input from 0 V, load
the DAC with all 0s, and adjust the VREF− voltage until VOUT
= 0 V.
• For gain adjustment, the AD7846 should be loaded with all
1s and R1 adjusted until VOUT = 10 (65,535)/(65,536) =
9.999847 V. If a simple resistor divider is used to vary the
VREF− voltage, it is important that the temperature
coefficients of these resistors match that of the DAC input
resistance (−300 ppm/°C). Otherwise, extra offset errors are
introduced over temperature. Many circuits do not require
these offset and gain adjustments. In these circuits, R1 can
be omitted. Pin 5 of the AD586 can be left open circuit and
Pin 8 (VREF−) of the AD7846 tied to 0 V.
AD7846
Rev. G | Page 14 of 24
BIPOLAR OPERATION
Figure 24 shows the AD7846 set up for ±10 V bipolar operation.
The AD588 provides precision ±5 V tracking outputs that are
fed to the VREF+ and VREF− inputs of the AD7846. The code table
for Figure 24 is shown in Table 9.
DGND
+15
V
+5
V
V
DD
V
SS
V
CC
V
OUT
R
IN
V
REF+
V
REF–
R2
10k
Ω
C1
1µF
SIGNAL
GROUND
–15V
*
ADDITIONAL PINS OMITTED FOR CLARITY
AD7846*
AD588
V
OUT
(–10V TO +10V)
+15V
–15V
R3
100kΩ
R1
39kΩ
+15
V
421
9
5
6
20
7
2
3
1
14
15
16
13812
11
10
5
9
7
46
8
0
8490-024
Figure 24. Bipolar ±10 V Operation
Table 9. Offset Binary Code Table for Figure 24
Binary Number in DAC Latch
MSB LSB1 Analog Output (VOUT)
1111 1111 1111 1111 +10 (32,767/32,768) V
1000 0000 0000 0001 +10 (1/32,768) V
1000 0000 0000 0000 0 V
0111 1111 1111 1111 −10 (1/32,768) V
0000 0000 0000 0000 −10 (32,768/32,768) V
1 LSB = 10 V/215 = 10 V/32,768 = 305 V.
Full-scale and bipolar zero adjustment are provided by varying
the gain and balance on the AD588. R2 varies the gain on the
AD588 while R3 adjusts the +5 V and −5 V outputs together
with respect to ground.
For bipolar zero adjustment on the AD7846, load the DAC with
100…000 and adjust R3 until VOUT = 0 V. Full scale is adjusted
by loading the DAC with all 1s and adjusting R2 until VOUT =
9.999694 V.
When bipolar zero and full-scale adjustment are not needed, R2
and R3 can be omitted, Pin 12 on the AD588 should be connected
to Pin 11, and Pin 5 should be left floating. If a user wants a 5 V
output range, there are two choices. By tying Pin 6 (RIN) of the
AD7846 to VOUT (Pin 5), the output stage gain is reduced to
unity and the output range is ±5 V. If only a positive 5 V reference
is available, bipolar ±5 V operation is still possible. Tie VREF− to
0 V and connect RIN to VREF+. This also gives a ±5 V output
range. However, the linearity, gain, and offset error specifications
are the same as the unipolar 0 V to 5 V range.
MULTIPLYING OPERATION
The AD7846 is a full multiplying DAC. To obtain four-quadrant
multiplication, tie VREF− to 0 V, apply the ac input to VREF+, and
tie RIN to VREF+. Figure 11 shows the large signal frequency
response when the DAC is used in this fashion.
AD7846
Rev. G | Page 15 of 24
POSITION MEASUREMENT APPLICATION
Figure 25 shows the AD7846 in a position measurement applica-
tion using an linear variable displacement transducer (LVDT),
an AD630 synchronous demodulator and a comparator to make
a 16-bit LVDT-to-digital converter. The LVDT is excited with a
fixed frequency and fixed amplitude sine wave (usually 2.5 kHz,
2 V p-p). The outputs of the secondary coil are in antiphase and
their relative amplitudes depend on the position of the core in the
LVDT. The AD7846 output interpolates between these two inputs
in response to the DAC input code. The AD630 is set up so that
it rectifies the DAC output signal. Thus, if the output of the DAC is
in phase with the VREF+ input, the inverting input to the compara-
tor is positive, and if it is in phase with VREF−, the output is nega-
tive. By turning on each bit of the DAC in succession starting
with the MSB and deciding to leave it on or turn it off based on
the comparator output, a 16-bit measurement of the core position
is obtained.
AD7846*
LVDT
DB0DB15
R1
100kΩ
C1
1µF
PROCESSOR DATA BUS
SIGNAL
GROUND
TO
PROCESSOR PORT
*ADDITIONAL PINS OMITTED FOR CLARITY
x ASIN ω t
–(1–x) ASIN ω t
A
SIN ω t
AD630*
DGND
V
OUT
R
IN
V
REF+
V
REF–
6
20
75
8
10
13
10
916
3
08490-027
Figure 25. AD7846 in Position Measurement Application
AD7846
Rev. G | Page 16 of 24
MICROPROCESSOR INTERFACING
AD7846-TO-8086 INTERFACE
Figure 26 shows the 8086 16-bit processor interfacing to the
AD7846. The double buffering feature of the DAC is not used in
this circuit because LDAC is permanently tied to 0 V. AD0 to
AD15 (the 16-bit data bus) are connected to the DAC data bus
(DB0 to DB15). The 16-bit word is written to the DAC in one
MOV instruction and the analog output responds immediately.
In this example, the DAC address is 0xD000.
AD7846*
+5V
DATA BUS
CS
LDAC
CLR
R/W
DB0 TO DB15
16-BIT
LATCH
8086
ALE
DEN
RD
WR
AD0 TO AD15
ADDRESS
DECODE
ADDRESS BUS
08490-028
*LINEAR CIRCUITRY OMITTED FOR CLARITY
Figure 26. AD7846-to-8086 Interface Circuit
In a multiple DAC system, the double buffering of the AD7846
allows the user to simultaneously update all DACs. In Figure 27,
a 16-bit word is loaded to the input latches of each of the DACs
in sequence. Then, with one instruction to the appropriate
address, CS4 (that is, LDAC) is brought low, updating all the
DACs simultaneously.
+5V
DATA BUS
*LINEAR CIRCUITRY OMITTED FOR CLARITY
16-BIT
LATCH
ADDRESS
DECODE
ADDRESS BUS
AD7846*
CS
LDAC
R/W
DB0 TO DB15
8086
ALE
DEN
RD
WR
AD0 TO AD15
CLR
CLR +5V
CLR +5V
AD7846*
CS
LDAC
R/W
DB0 TO DB15
AD7846*
CS
LDAC
R/W
DB0 TO DB15
08490-029
Figure 27. AD7846-to-8086 Interface: Multiple DAC System
AD7846-TO-MC68000 INTERFACE
Interfacing between the AD7846 and MC68000 is accomplished
using the circuit of Figure 28. The following routine writes data
to the DAC latches and then outputs the data via the DAC latch.
1
000 MOVE.W #W,
D0 The desired DAC dat
a
,
W, is loaded into
Data Register 0. W
may be any value
between 0 and 65535
(decimal) or 0 and
FFFF (hexadecimal).
MOVE.W
D0,
$
E000 The data, W, is
transferred between
D0 and the DAC
register.
MOVE.W
TRAP
#
228,
D7
#14
Control is returned
to the System Monitor
using these two
instructions.
AD7846*
+5V
DATA BUS
CS
LDAC
CLR
R/W
MC68000
DS
DTACK
R/W
A1 TO A23
ADDRESS
DECODE
ADDRESS BUS
D0 TO D15 DB0 TO DB15
0
8490-030
*
LINEAR CIRCUITRY OMITTED FOR CLARITY
Figure 28. AD7846-to-MC68000 Interface
AD7846
Rev. G | Page 17 of 24
DIGITAL FEEDTHROUGH
In the preceding interface configurations, most digital inputs to
the AD7846 are directly connected to the microprocessor bus.
Even when the device is not selected, these inputs are constantly
changing. The high frequency logic activity on the bus can feed
through the DAC package capacitance to show up as noise on
the analog output. To minimize this digital feedthrough, isolate
the DAC from the noise source. Figure 29 shows an interface
circuit that isolates the DAC from the bus.
Note that to make use of the AD7846 readback feature using
the isolation technique of Figure 29, the latch needs to be
bidirectional.
AD7846*
+5V
DATA BUS
CS
LDAC
CLR
MICRO-
PROCESSOR
A1 TO A15
ADDRESS
DECODE
ADDRESS BUS
D0 TO D15 DB0 TO DB15
R/W R/W
2×
74LS245
B BUS A BUS
DIR G
08490-031
*LINEAR CIRCUITRY OMITTED FOR CLARITY
Figure 29. AD7846 Interface Circuit Using Latches to Minimize Digital Feedthrough
AD7846
Rev. G | Page 18 of 24
APPLICATION HINTS
NOISE
In high resolution systems, noise is often the limiting factor.
With a 10 V span, a 16-bit LSB is 152 V (–96 dB). Thus, the
noise floor must stay below −96 dB in the frequency range of
interest. Figure 12 shows the noise spectral density for the
AD7846.
GROUNDING
As well as noise, the other prime consideration in high resolution
DAC systems is grounding. With an LSB size of 152 V and a
load current of 5 mA, 1 LSB of error can be introduced by series
resistance of only 0.03 .
Figure 30 shows recommended grounding for the AD7846 in a
typical application.
ANALOG SUPPLY DIGITAL SUPPLY
–15V+15V 0V DGND+5V
SIGNAL
GROUND
AD7846*
AD588*
R1
R4
R
L
V
OUT
(+5V TO –5V)
R2
R3
R5
*
ADDITIONAL PINS OMITTED FOR CLARIT
Y
2 9 16 4 9 21 20
6
5
1
3
7
8
15
14
08490-032
Figure 30. AD7846 Grounding
R1 to R5 represent lead and track resistances on the printed
circuit board. R1 is the resistance between the analog power
supply ground and the signal ground. Because current flowing
in R1 is very low (bias current of AD588 sense amplifier), the
effect of R1 is negligible. R2 and R3 represent track resistance
between the AD588 outputs and the AD7846 reference inputs.
Because of the force and sense outputs on the AD588, these
resistances will also have a negligible effect on accuracy.
R4 is the resistance between the DAC output and the load. If RL
is constant, then R4 introduces a gain error only that can be
trimmed out in the calibration cycle. R5 is the resistance
between the load and the analog common. If the output voltage
is sensed across the load, R5 introduces a further gain error,
which can be trimmed out. If, on the other hand, the output
voltage is sensed at the analog supply common, R5 appears as
part of the load and therefore introduces no errors.
PRINTED CIRCUIT BOARD LAYOUT
Figure 31 shows the AD7846 in a typical application with the
AD588 reference, producing an output analog voltage in the
±10 V range. Full-scale and bipolar zero adjustment are
provided by Potentiometer R2 and Potentiometer R3. Latches
(2 × 74LS245) isolate the DAC digital inputs from the active
microprocessor bus and minimize digital feedthrough.
AD7846
Rev. G | Page 19 of 24
2
3
5
6
7
8
9
4
18
17
15
14
13
12
11
16
10 119
20
V
OUT
(+10V TO –10V)
2
3
5
6
7
8
9
4
18
17
15
14
13
12
11
16
10 119
20
C4/A4
C5/A5
C6/A6
C7/A7
C8/A8
C9/A9
C10/A10
C11/A11
C12/A12
C13/A13
C14/A14
C15/A15
C16/A16
C17/A17
C18/A18
C19/A19
C20/A20
C21/A21
C22/A22
C23/A23
C32/A32
C31/A31
DB15
DB14
DB13
DB12
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
LDAC
CLR
CS
R/W
V
OUT
R
IN
V
SS
V
REF–
V
REF+
AD7846
J1
74LS245
74LS245
AD588
DGND
R2
100kΩ
C1
10µF
R3
100kΩ
R1
39kΩ
C12
1µF
C2
0.1µF
C4
0.1µF
C3
10µF
–15V
+15
V
C5
10µF
C6
0.1µF
C7
0.1µF
+5V
+5V
18
17
16
15
14
13
12
11
10
214
7
3
264
7
5
10
11
12
813 9
1
14
15
16
8
9
20
6
5
19
26
27
28
22
23
24
25
1
2
3
08490-033
Figure 31. Schematic for AD7846 Board
AD7846
Rev. G | Page 20 of 24
OUTLINE DIMENSIONS
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
28
114
15
0.610 (15.49)
0.500 (12.70)
0.005 (0.13)
MIN
0.100 (2.54)
MAX
0.620 (15.75)
0.590 (14.99)
0.018 (0.46)
0.008 (0.20)
SEATING
PLANE
0.225(5.72)
MAX
1.490 (37.85) MAX
0.150 (3.81)
MIN
0.200 (5.08)
0.125 (3.18)
0.015 (0.38)
MIN
0.026 (0.66)
0.014 (0.36)
0.100
(2.54)
BSC
0.070 (1.78)
0.030 (0.76)
15°
0°
PIN 1
030106-A
Figure 32. 28-Lead Ceramic Dual In-Line Package [CERDIP]
(Q-28-2)
Dimensions shown in inches and (millimeters)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
CORNER LEADS MAY BE CONFIGURED AS WHOLE LEADS.
COMPLIANT TO JEDEC STANDARDS MS-0 11
071006-A
0.100 (2.54)
BSC
1.565 (39.75)
1.380 (35.05)
0.580 (14.73)
0.485 (12.31)
0.022 (0.56)
0.014 (0.36)
0.200 (5.08)
0.115 (2.92)
0.070 (1.78)
0.050 (1.27)
0.250 (6.35)
MAX
SEATING
PLANE
0.015
(0.38)
MIN
0.005 (0.13)
MIN
0.700 (17.78)
MAX
0.015 (0.38)
0.008 (0.20)
0.625 (15.88)
0.600 (15.24)
0.015 (0.38)
GAUGE
PLANE
0.195 (4.95)
0.125 (3.17)
28
114
15
Figure 33. 28-Lead Plastic Dual In-Line Package [PDIP]
Wide Body
(N-28-2)
Dimensions shown in inches and (millimeters)
AD7846
Rev. G | Page 21 of 24
1
28
5
11
18
BOTTON
VIEW
19 25
26
412
0.15 (3.81)
REF
0.075
(1.91)
REF
0.028 (0.71)
0.022 (0.56)
0.300 (7.62)
REF
0.055 (1.40)
0.045 (1.14)
0.075 (1.91)
REF
0.020 (0.51)
MIN
0.05 (1.27)
0.095 (2.41)
0.075 (1.90)
0.458 (11.63)
0.442 (11.23) SQ
0.458
(11.63)
MAX
SQ
0.100 (2.54)
0.064 (1.63)
0.088 (2.24)
0.054 (1.37)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
022106-A
Figure 34. 28-Terminal Ceramic Leadless Chip Carrier [LCC]
(E-28-1)
Dimensions shown in inches and (millimeters)
COMPLIANT TO JEDEC STANDARDS MO-047-AB
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
4
5
26
25
11
12
19
18
TOP VIEW
(PINS DOWN)
SQ
0.456 (11.582)
0.450 (11.430)
0.050
(1.27)
BSC
0.048 (1.22)
0.042 (1.07)
0.048 (1.22)
0.042 (1.07)
0.495 (12.57)
0.485 (12.32) SQ
0.021 (0.53)
0.013 (0.33)
0.430 (10.92)
0.390 (9.91)
0.032 (0.81)
0.026 (0.66)
0.120 (3.04)
0.090 (2.29)
0.056 (1.42)
0.042 (1.07) 0.020 (0.51)
MIN
0.180 (4.57)
0.165 (4.19)
BOTTOM
VIEW
(PINS UP)
0.045 (1.14)
0.025 (0.64) R
PIN 1
IDENTIFIER
042508-A
Figure 35. 28-Lead Plastic Leaded Chip Carrier [PLCC]
(P-28)
Dimensions shown in inches and (millimeters)
AD7846
Rev. G | Page 22 of 24
ORDERING GUIDE
Model1 Temperature Range Relative Accuracy Package Description Package Option
5962-89697013A −55°C to +125°C ±16 LSB 28-Terminal Ceramic Leadless Chip Carrier [LCC] E-28-1
5962-8969701XA −55°C to +125°C ±16 LSB 28-Lead Ceramic Dual In-Line Package [CERDIP] Q-28-2
AD7846JN 0°C to +70°C ±16 LSB 28-Lead Plastic Dual In-Line Package [PDIP] N-28-2
AD7846JNZ 0°C to +70°C ±16 LSB 28-Lead Plastic Dual In-Line Package [PDIP] N-28-2
AD7846KN 0°C to +70°C ±8 LSB 28-Lead Plastic Dual In-Line Package [PDIP] N-28-2
AD7846KNZ 0°C to +70°C ±8 LSB 28-Lead Plastic Dual In-Line Package [PDIP] N-28-2
AD7846JP 0°C to +70°C ±16 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846JP-REEL 0°C to +70°C ±16 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846JPZ 0°C to +70°C ±16 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846JPZ-REEL 0°C to +70°C ±16 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846KP 0°C to +70°C ±8 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846KP-REEL 0°C to +70°C ±8 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846KPZ 0°C to +70°C ±8 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846KPZ-REEL 0°C to +70°C ±8 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846AP −40°C to +85°C ±16 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846APZ −40°C to +85°C ±16 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846AQ −40°C to +85°C ±16 LSB 28-Lead Ceramic Dual In-Line Package [CERDIP] Q-28-2
AD7846BP −40°C to +85°C ±8 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846BPZ −40°C to +85°C ±8 LSB 28-Lead Plastic Leaded Chip Carrier [PLCC] P-28
AD7846ACHIPS −40°C to +85°C ±16 LSB DIE
1 Z = RoHS Compliant Part.
AD7846
Rev. G | Page 23 of 24
NOTES
AD7846
Rev. G | Page 24 of 24
NOTES
©2000–2010 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08490-0-4/10(G)
