AD7417ARZREEL - ANALOG DEVICES - Datasheet.Directory

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MOS

Dual 12-Bit Serial DACPORT

AD7249

GENERAL DESCRIPTION

The AD7249 DACPORT contains a pair of 12-bit, voltage-

output, digital-to-analog converters with output amplifiers and

Zener voltage reference on a monolithic CMOS chip. No exter-

nal trims are required to achieve full specified performance.

The output amplifiers are capable of developing +10 V across a

2 kΩ load. The output voltage ranges with single supply opera-

tion are 0 V to +5 V or 0 V to +10 V, while an additional bipolar

±5 V output range is available with dual supplies. The ranges

are selected using the internal gain resistor.

Interfacing to the AD7249 is serial, minimizing pin count and

allowing a small package size. Standard control signals allow

interfacing to most DSP processors and microcontrollers. The

data stream consists of 16 bits, DB15 to DB13 are don’t care

bits, the 13th bit (DB12) is used as the channel select bit and

the remaining 12 bits (DB11 to DB0) contain the data to update

the DAC. The 16-bit data word is clocked into the input register

on each falling SCLK edge.

The data format is natural binary in both unipolar ranges, while

either offset binary or twos complement format may be selected

in the bipolar range. A CLR function is provided which sets the

output to 0 V in both unipolar ranges and in the twos comple-

ment bipolar range, while with offset binary data format, the

output is set to –REFIN. This function is useful as a power-on

reset as it allows the outputs to be set to a known voltage level.

The AD7249 features a serial interface which allows easy con-

nection to both microcomputers and 16-bit digital signal proces-

sors with serial ports. The serial data may be applied at rates up

to 2 MHz allowing a DAC update rate of 125 kHz.

The AD7249 is fabricated on linear compatible CMOS

(LC

MOS), an advanced, mixed technology process. It is pack-

aged in 16-lead DIP and 16-lead SOIC packages.

PRODUCT HIGHLIGHTS

1. Two complete 12-bit DACPORTs

The AD7249 contains two complete voltage output, 12-bit

DACs in both 16-lead DIP and SOIC packages.

2. Single or dual supply operation

3. Minimum 3-wire interface to most DSP processors

4. DAC update rate—125 kHz

FUNCTIONAL BLOCK DIAGRAM

FEATURES

Two 12-Bit CMOS DAC Channels with

On-Chip Voltage Reference

Output Amplifiers

Three Selectable Output Ranges per Channel

–5 V to +5 V, 0 V to +5 V, 0 V to +10 V

Serial Interface

125 kHz DAC Update Rate

Small Size: 16-Lead DIP or SOIC

Low Power Dissipation

APPLICATIONS

Process Control

Industrial Automation

Digital Signal Processing Systems

Input/Output Ports

DACPORT is a registered trademark of Analog Devices, Inc.

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: © Analog Devices, Inc.,

12-BIT

DAC A

12-BIT

DAC B

INPUT SHIFT REGISTER

AD7249

REFOUT

REFIN

AGND

DGND

OFSA

OUTA

OFSB

OUTB

SCLK SDIN BIN/COMP CLR LDACSYNC

REV. D

2013

781/461-3113

AD7249* PRODUCT PAGE QUICK LINKS

Last Content Update: 02/23/2017

COMPARABLE PARTS

View a parametric search of comparable parts.

DOCUMENTATION

Application Notes

•AN-214: Ground Rules for High Speed Circuits

•AN-225: 12-Bit Voltage-Output DACs for Single-Supply 5V

and 12V Systems

•AN-348: Avoiding Passive-Component Pitfalls

Data Sheet

•AD7249: LC2MOS Dual 12-Bit Serial DACPORT® Data Sheet

REFERENCE MATERIALS

Solutions Bulletins & Brochures

•Digital to Analog Converters ICs Solutions Bulletin

DESIGN RESOURCES

•AD7249 Material Declaration

•PCN-PDN Information

•Quality And Reliability

•Symbols and Footprints

DISCUSSIONS

View all AD7249 EngineerZone Discussions.

SAMPLE AND BUY

Visit the product page to see pricing options.

TECHNICAL SUPPORT

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number.

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–2–

AD7249–SPECIFICATIONS

(VDD = +12 V to +15 V,1 VSS = O V or –12 V to –15 V,1 AGND = DGND = O V, REFIN =

+5 V, RL = 2 k⍀, CL = 100 pF to AGND. All specifications TMIN to TMAX unless otherwise noted.)

Parameter A Version

B Version

S Version

Unit Test Conditions/Comments

STATIC PERFORMANCE

Resolution 12 12 12 Bits

Relative Accuracy

±1±1/2 ±1 LSB max

Differential Nonlinearity

±0.9 ±0.9 ±0.9 LSB max Guaranteed Monotonic

Unipolar Offset Error

±5±5±6 LSB max V

= 0 V or –12 V to –15 V

; DAC

Latch Contents All 0s

Bipolar Zero Error

±6±5±7 LSB max V

= –12 V to –15 V

DAC Latch Contents All 0s

Full-Scale Error

3, 4

±6±6±7 LSB max

Full-Scale Temperature Coefficient ±5±5±5 ppm of FSR/°C typ

REFERENCE OUTPUT

REFOUT 4.95/5.05 4.95/5.05 4.95/5.05 V min/V max

Reference Temperature Coefficient ±25 ±25 ±30 ppm/°C typ

Reference Load Change

(∆V

REFOUT

vs. I

) –1 –1 –1 mV max Reference Load Current (I

)

Change (0 µA–100 µA)

REFERENCE INPUT

Reference Input Range, REFIN 4.95/5.05 4.95/5.05 4.95/5.05 V min/V max 5 V ± 1%

Input Current 5 5 5 µA max

DIGITAL INPUTS

Input High Voltage, V

INH

2.4 2.4 2.4 V min

Input Low Voltage, V

INL

0.8 0.8 0.8 V max

Input Current

±1±1±1µA max V

= 0 V to V

Input Capacitance

8 8 8 pF max

ANALOG OUTPUTS

Output Range Resistor,

OFSA

& R

OFSB

15/30 15/30 15/30 kΩ min/ max

Output Voltage Ranges

+5, +10 +5, +10 +5, +10 V Single Supply; V

= 0 V

Output Voltage Ranges

+5, +10, ±5 +5, +10, ±5 +5, +10, ±5 V Dual Supply; V

= –12 V or –15 V

DC Output Impedance 0.5 0.5 0.5 Ω typ

AC CHARACTERISTICS

Voltage Output Settling-Time Settling Time to Within

±1/2 LSB of Final Value

Positive Full-Scale Change 10 10 10 µs max Typically 3 µs

Negative Full-Scale Change 10 10 10 µs max Typically 5 µs

Digital-to-Analog Glitch Impulse

30 30 30 nV secs typ 1 LSB Change Around

Major Carry

Digital Feedthrough

10 10 10 nV secs typ

Digital Crosstalk

10 10 10 nV secs typ

POWER REQUIREMENTS

Range +10.8/+16.5 +11.4/+15.75 +11.4/+15.75 V min/V max For Specified Performance Unless

Otherwise Stated

Range (Dual Supplies) –10.8/–16.5 –11.4/–15.75 –11.4/–15.75 V min/V max For Specified Performance Unless

Otherwise Stated

15 15 15 mA max Output Unloaded; Typically 11 mA

(Dual Supplies) 5 5 5 mA max Output Unloaded; Typically 3 mA

NOTES

Power supply tolerance, A Version: ±10%; B, S Versions: ±5%.

Temperature ranges are as follows: A, B Versions: –40°C to +85°C; S Version: –55°C to +125°C.

See Terminology.

Measured with respect to REFIN and includes unipolar/bipolar offset error.

Guaranteed by design not production tested.

0 V to 10 V output range available only with V

≥ 14.25 V.

Specifications subject to change without notice.

REV. D

AD7249

–3–

TIMING CHARACTERISTICS

1, 2

Limit at T

MIN

to T

MAX

Parameter (All Versions) Unit Conditions/Comments

200 ns min SCLK Cycle Time

15 ns min SYNC to SCLK Falling Edge Setup Time

50 ns min SYNC to SCLK Hold Time

0 ns min Data Setup Time

150 ns min Data Hold Time

0 ns min SYNC High to LDAC Low

20 ns min LDAC Pulsewidth

0 ns min LDAC High to SYNC Low

50 ns min CLR Pulsewidth

20 ns min SYNC High Time

NOTES

Timing specifications guaranteed by design not production tested. All input signals are specified with tr = tf = 5 ns (10% to 90% of 5 V) and timed from a voltage

level of 1.6 V.

See Figure 8.

Power supply tolerance, A Version: ±10%; B, S Versions: ±5%.

SCLK Mark/Space Ratio range is 45/55 to 55/45.

(VDD = +12 V to +15 V,3 VSS = 0 V or –12 V to –15 V,3 AGND = DGND = 0 V, RL = 2 k⍀,

CL = 100 pF. All specifications TMIN to TMAX unless otherwise noted.)

ABSOLUTE MAXIMUM RATINGS

= +25°C unless otherwise noted)

to AGND, DGND . . . . . . . . . . . . . . . . . . –0.3 V to +17 V

to AGND, DGND . . . . . . . . . . . . . . . . . . +0.3 V to –17 V

AGND to DGND . . . . . . . . . . . . . . . . . –0.3 V to V

+ 0.3 V

OUTA, B2

to AGND . . . . . . . . . . . . V

– 0.3 V to V

+ 0.3 V

REFOUT to AGND . . . . . . . . . . . . . . . . . . . . . . . . 0 V to V

REFIN to AGND . . . . . . . . . . . . . . . . . –0.3 V to V

+ 0.3 V

Digital Inputs to DGND . . . . . . . . . . . . –0.3 V to V

+ 0.3 V

Operating Temperature Range

Industrial (A, B Versions) . . . . . . . . . . . . . . –40°C to +85°C

Extended (S Version) . . . . . . . . . . . . . . . . . –55°C to +125°C

Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . +150°C

Storage Temperature Range . . . . . . . . . . . . . –65°C to +150°C

Power Dissipation Plastic DIP . . . . . . . . . . . . . . . . . . . 600 mW

Thermal Impedance . . . . . . . . . . . . . . . . . . . . +117°C/W

Lead Temperature (Soldering, 10 secs) . . . . . . . . . . +300°C

Power Dissipation, Cerdip . . . . . . . . . . . . . . . . . . . . . . 600 mW

Thermal Impedance . . . . . . . . . . . . . . . . . . . . . . 76°C/W

Lead Temperature (Soldering, 10 secs) . . . . . . . . . . +300°C

Power Dissipation, SOIC . . . . . . . . . . . . . . . . . . . . . . . 600 mW

Thermal Impedance . . . . . . . . . . . . . . . . . . . . . . 75°C/W

Lead Temperature (Soldering)

Vapor Phase (60 secs) . . . . . . . . . . . . . . . . . . . . . . +215°C

Infrared (15 secs) . . . . . . . . . . . . . . . . . . . . . . . . . +220°C

NOTES

Stresses above those listed under Absolute Maximum Ratings may cause perma-

nent damage to the device. This is a stress rating only; functional operation of the

device at these or any other conditions above those listed in the operational

sections of this specification is not implied. Exposure to absolute maximum rating

conditions for extended periods may affect device reliability. Only one Absolute

Maximum Rating may be applied at any time.

The outputs may be shorted to voltages in this range provided the power dissipation

of the package is not exceeded.

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 AD7249 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

REV. D

–4–

AD7249

PIN FUNCTION DESCRIPTION (DIP & SOIC PIN NUMBERS)

Pin Mnemonic Description

11 REFOUT Voltage Reference Output. The internal 5 V analog reference is provided at this pin. To operate the

part using its internal reference, REFOUT should be connected to REFIN.

12 REFIN Voltage Reference Input. It is internally buffered before being applied to both DACs. The nominal

reference voltage for specified operation of the AD7249 is 5 V.

13R

OFSB

Output Offset Resistor for the amplifier of DAC B. It is connected to V

OUTB

for the +5 V range, to

AGND for the +10 V range and to REFIN for the –5 V to +5 V range.

14V

OUTB

Analog Output Voltage of DAC B. This is the buffer amplifier output voltage. Three different output

voltage ranges can be chosen: 0 V to +5 V, 0 V to +10 V and –5 V to +5 V.

15 AGND Analog Ground. Ground reference for all analog circuitry.

16CLR Clear, Logic Input. Taking this input low clears both DACs. It sets V

OUTA

and V

OUTB

to 0 V in both

unipolar ranges and the twos complement bipolar range and to –REFIN in the offset binary bipolar

range.

17BIN/COMP Logic Input. This input selects the data format to be either binary or twos complement. In both uni-

polar ranges natural binary format is selected by connecting this input to a Logic “0”. In the bipolar

configuration offset binary format is selected with a Logic “0” while a Logic “1” selects twos complement.

18 DGND Digital Ground. Ground reference for all digital circuitry.

19 SDIN Serial Data In, Logic Input. The 16-bit serial data word is applied to this input.

10 LDAC Load DAC, Logic Input. Updates both DAC outputs. The DAC outputs are updated on the falling

edge of this signal or alternatively if this line is permanently low, an automatic update mode is se-

lected whereby both DACs are updated on the 16th falling SCLK pulse.

11 SCLK Serial Clock, Logic Input. Data is clocked into the input register on each falling SCLK edge.

12 SYNC Data Synchronization Pulse, Logic Input. Taking this input low initializes the internal logic in readi-

ness for a new data word.

13 V

Positive Power Supply.

14 V

OUTA

Analog Output Voltage of DAC A. This is the buffer amplifier output voltage. Three different output

voltage ranges can be chosen: 0 V to +5 V, 0 V to +10 V and –5 V to +5 V.

15 V

Negative Power Supply (used for the output amplifier only) may be connected to 0 V for single sup-

ply operation or –12 V to –15 V for dual supplies.

16 R

OFSA

Output Offset Resistor for the amplifier of DAC A. It is connected to V

OUTA

for the +5 V range, to

AGND for the +10 V range and to REFIN for the –5 V to +5 V range.

PIN CONFIGURATIONS

(DIP and SOIC)

TOP VIEW

(Not to Scale)

REFOUT ROFSA

AD7249

REFIN VSS

ROFSB VOUTA

VOUTB VDD

AGND SYNC

CLR SCLK

BIN/COMP LDAC

DGND SDIN

REV. D

AD7249

–5–

TERMINOLOGY

Bipolar Zero Error

Bipolar Zero Error is the voltage measured at V

OUT

when the

DAC is configured for bipolar output and loaded with all 0s

(Twos Complement Coding) or with 1000 0000 0000 (Offset

Binary Coding). It is due to a combination of offset errors in the

DAC, amplifier and mismatch between the internal gain resis-

tors around the amplifier.

Full-Scale Error

Full-Scale Error is a measure of the output error when the am-

plifier output is at full scale (for the bipolar output range full

scale is either positive or negative full scale). It is measured with

respect to the reference input voltage and includes the offset

errors.

Digital-to-Analog Glitch Impulse

This is the voltage spike that appears at V

OUT

when the digital

code in the DAC Latch changes, before the output settles to its

final value. It is normally specified as the area of the glitch in

nV-secs and is measured when the digital code is changed by

1 LSB at the major carry transition (0111 1111 1111 to 1000

0000 0000 or 1000 0000 0000 to 0111 1111 1111).

Digital Feedthrough

This is a measure of the voltage spike that appears on V

OUT

as a

result of feedthrough from the digital inputs on the AD7249. It

is measured with LDAC held high.

Relative Accuracy (Linearity)

Relative Accuracy, or endpoint linearity, is a measure of the

maximum deviation of the DAC transfer function from a

straight line passing through the endpoints of the transfer func-

tion. It is measured after allowing for zero and full-scale errors

and is expressed in LSBs or as a percentage of full-scale reading.

Single Supply Linearity and Gain Error

The output amplifier on the AD7249 can have true negative

offsets even when the part is operated from a single +15 V sup-

ply. However, because the negative supply rail (V

) is 0 V, the

output cannot actually go negative. Instead, when the output

offset voltage is negative, the output voltage sits at 0 V, resulting

in the transfer function shown in Figure 1.

DAC CODE

OUTPUT

VOLTAGE

NEGATIVE

OFFSET

Figure 1. Effect of Negative Offset (Single Supply)

This “knee” is an offset effect, not a linearity error, and the

transfer function would have followed the dotted line if the

output voltage could have gone negative.

Normally, linearity is measured between zero (all 0s input code)

and full scale (all 1s input code) after offset and full scale have

been adjusted out or allowed for, but this is not possible in

single supply operation if the offset is negative, due to the knee

in the transfer function. Instead, linearity of the AD7249 in the

unipolar mode is measured between full scale and the lowest

code which is guaranteed to produce a positive output voltage.

This code is calculated from the maximum specification for

negative offset. For the A and B versions, the linearity is mea-

sured between Codes 3 and 4095. For the S grade, linearity is

measured between Code 5 and Code 4095.

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 or less

over the operating temperature range ensures monotonicity.

Unipolar Offset Error

Unipolar Offset Error is the measured output voltage from V

OUT

with all zeros loaded into the DAC latch, when the DAC is

configured for unipolar output. It is due to a combination of the

offset errors in the DAC and output amplifier.

CIRCUIT INFORMATION

D/A Section

The AD7249 contains two 12-bit voltage-mode D/A converters

consisting of highly stable thin film resistors and high-speed

NMOS single-pole, double-throw switches. The simplified

circuit diagram for the DAC section is shown in Figure 2. The

output voltage from the converter has the same polarity as the

reference voltage, REFIN, allowing single supply operation.

2R 2R

2R 2R 2R 2R 2R 2R

R RRRR

REFIN*

AGND

*BUFFERED REFIN VOLTAGE

ROFS

VOUT

SHOWN FOR ALL 1s

ON DAC

Figure 2. D/A Simplified Circuit Diagram

REV. D

–6–

AD7249

Internal Reference

The AD7249 has an on-chip temperature compensated buried

Zener reference which is factory trimmed to 5 V ± 50 mV. The

reference voltage is provided at the REFOUT pin. This refer-

ence can be used to provide the reference voltage for the D/A

converter by connecting the REFOUT pin to the REFIN pin.

The reference voltage can also be used as a reference for other

components and is capable of providing up to 500 µA to an

external load. The maximum recommended capacitance on

REFOUT for normal operation is 50 pF. If the reference output

is required to drive a capacitive load greater than 50 pF, then a

200 Ω resistor should be placed in series with the capacitive

load. Figure 3 shows the suggested REF OUT decoupling

scheme, a 200 Ω resistor and the parallel combination of a

10 µF tantalum and a 0.1 µF ceramic capacitor. This decoupling

scheme reduces the noise spectral density of the reference.

REFOUT 200⍀

10␮F0.1␮F

EXT LOAD

Figure 3. Reference Decoupling Scheme

External Reference

In some applications, the user may require a system reference or

some other external reference to drive the AD7249. References

such as the AD586 provide an ideal external reference source

(See Figure 10). The REFIN voltage is internally buffered by a

unity gain amplifier before being applied to the D/A converter.

The D/A converter is scaled for a 5 V reference and the device is

tested with 5 V applied to REFIN. Other reference voltages may

be used with degraded performance. Figure 4 shows the degra-

dation in linearity vs. REFIN.

REFIN – Volts

1.0

LINEARITY ERROR – LSBs

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0 34567 89

= +15V

= –15V

= +25ⴗC

INL

DNL

Figure 4. Linearity vs. REFIN Voltage

Op Amp Section

The output of the voltage-mode D/A converter is buffered by a

noninverting CMOS amplifier. The R

OFS

input allows three

output voltage ranges to be selected. The buffer amplifier is

capable of developing +10 V across a 2 kΩ load to AGND.

The output amplifier can be operated from a single +15 V sup-

ply by tying V

= 0 V.

The amplifier can also be operated from dual supplies to allow

an additional bipolar output range of –5 V to +5 V. Dual sup-

plies are necessary for the bipolar output range but can also be

used for the unipolar ranges to give faster settling time to volt-

ages near 0 V, to allow full sink capability of 2.5 mA over the

entire output range and to eliminate the effects of negative offsets

on the transfer characteristic (outlined previously). A plot of the

output sink capability of the amplifier is shown in Figure 5.

OUTPUT VOLTAGE – Volts

SINK

– mA

0246810

= 0V

= –15V

Figure 5. Amplifier Sink Current

FREQUENCY – Hz

500

nV/ Hz

100 200 500 1k 2k 5k 10k

VDD = +15V

VSS = 0V

TA = +25ⴗC

200

100

REFERENCE DECOUPLING COMPONENTS ARE

A 200⍀ RESISTOR IN SERIES WITH A PARALLEL

COMBINATION OF 10␮F AND 0.1␮F TO GND.

20k 50k 100k

REFERENCE

(NO DECOUPLING)

REFERENCE

(DECOUPLED*)

OUTPUT WITH ALL

0s ON DAC

Figure 6. Noise Spectral Density vs. Frequency

REV. D

AD7249

–7–

DIGITAL INTERFACE

The AD7249 contains an input serial to parallel shift register

and a DAC latch for both DAC A and DAC B. A simplified

diagram of the input loading circuitry is shown in Figure 7.

Serial data on the SDIN input is loaded to the input register

under control of SYNC and SCLK. The SYNC input provides

the frame synchronization signal which tells the AD7249 that

valid serial data on the SDIN input will be available for the next

16 falling edges of SCLK. An internal counter/decoder circuit

provides a low gating signal so that only 16 data bits are clocked

into the input shift register. After 16 SCLK pulses the internal

gating signal goes inactive (high) thus locking out any further

clock pulses. Therefore either a continuous clock or a burst

clock source may be used to clock in the data. The SYNC input

is taken high after the complete 16-bit word is loaded in.

DAC selection is accomplished using the thirteenth bit (DB12)

of the serial data input stream. A zero in DB12 will select DAC

A while a one in this position selects DAC B. Although 16 bits

of data are clocked into the input register, only 12 bits get trans-

ferred into the DAC latch. The relevant DAC latch is deter-

mined by the value of the thirteenth bit and the first three bits

in the 16-bit stream are don’t cares. Therefore, the data format

is three don’t cares followed by the DAC selection bit and the

12-bit data word with the LSB as the last bit in the serial

stream.

There are two ways in which a DAC latches and hence the

analog outputs may be updated. The status of the LDAC input

is examined after SYNC is taken low. Depending on its status,

one of two update modes are selected.

If LDAC = 0, then the automatic update mode is selected. In

this mode the DAC latch and analog output are updated auto-

matically when the last bit in the serial data stream is clocked in.

The update thus takes place on the sixteenth falling SCLK edge.

If LDAC = 1, then the automatic update is disabled and both

DAC latches are updated by taking LDAC low any time after

the 16-bit data transfer is complete. The update now occurs on

the falling edge of LDAC. Note that the LDAC input must be

taken back high again before the next data transfer is initiated.

When a complete word is held in the shift register it may then

be loaded into the DAC latch under control of LDAC.

Clear Function (CLR)

The clear function clears the contents of the input shift register

and loads both DAC latches with all 0s. It is activated by taking

CLR low. In all ranges except the Offset Binary bipolar range

(–5 V to +5 V) the output voltage is reset to 0 V. In the offset

binary bipolar range the output is set to –REFIN. The clear

function is especially useful at power-up as it enables the output

to be reset to a known state.

SYNC

SCLK

SDIN

LDAC

CLR

GATING

SIGNAL

RESET

/16

COUNTER/

DECOUNTER

DECODER

AUTO-UPDATE

CIRCUITRY

CLK A

SDATA

CLK B

DAC LATCH A (12-BITS)

DAC LATCH B (12-BITS)

SHIFT REGISTER A

SHIFT REGISTER B

Figure 7. Simplified Loading Structure

REV. D

–8–

AD7249

DB15 DB14 DB13 DB12 DB11 DB0 DB15 DB14 DB13 DB12 DB10 DB0

DON'T

CARE

DON'T

CARE

DON'T

CARE

DAC

SELECT

MSB DON'T

CARE

DON'T

CARE

DON'T

CARE

DAC

SELECT

MSBLSB LSB

DAC A DAC B

SCLK

SYNC

SDIN

LDAC

CLR

Figure 8. Timing Diagram

TRANSFER FUNCTION

The internal scaling resistors provided on the AD7249 allow

several output voltage ranges. The part can produce unipolar

output ranges of 0 V to +5 V or 0 V to +10 V and a bipolar

output range of ±5 V. Connections for the various ranges are

outlined below. Since each DAC has its own R

OFS

input the two

DACs can be set up for different output ranges.

Unipolar (0 V to +10 V) Configuration

The first of the configurations provides an output voltage range

of 0 V to +10 V. This is achieved by connecting the output

offset resistor R

OFSA

, R

OFSB

(Pin 3, 16) to AGND. Natural Bi-

nary data format is selected by connecting BIN/COMP (Pin 7)

to DGND. In this configuration, the AD7249 can be operated

using either single or dual supplies. Note that the V

supply is

AD7249*

12-BIT

DAC A

12-BIT

DAC B

REFOUT

REFIN

OFSA

OUTA

0V TO 10V

OFSB

OUTB

0V TO 10V

BIN/COMP

DGNDAGND

0V OR V

*ADDITIONAL PINS OMITTED FOR CLARITY.

Figure 9. Unipolar (0 V to +10 V) Configuration

restricted to +15 V ± 10% for this range in order to maintain

sufficient amplifier headroom. Dual supplies may be used to

improve settling time and give increased current sink capability

for the amplifier. Figure 9 shows the connection diagram for

unipolar operation of the AD7249. Table I shows the digital

code vs. analog output for this configuration.

Unipolar (0 V to +5 V) Configuration

The 0 V to +5 V output voltage range is achieved by tying

OFSA

to V

OUTA

or R

OFSB

to V

OUTB

. Once again, the AD7249

can be operated using either single or dual supplies. The table

for output voltage versus digital code is as in Table I, with

2REFIN replaced by REFIN. Note, for this range, 1 LSB =

REFIN × (2

–12

) = (REFIN/4096).

Table I. Unipolar Code Table (0 V to +10 V Range)

Input Data Word

MSB LSB Analog Output, V

OUT

XXXY 1111 1111 1111 +2REFIN × (4095/4096)

XXXY 1000 0000 0001 +2REFIN × (2049/4096)

XXXY 1000 0000 0000 +2REFIN × (2048/4096) = +REFIN

XXXY 0111 1111 1111 +2REFIN × (2047/4096)

XXXY 0000 0000 0001 +2REFIN × (1/4096)

XXXY 0000 0000 0000 0 V

X = Don’t Care.

Y = DAC Select Bit, 0 = DAC A, 1= DAC B.

Note: 1 LSB = 2REFIN/4096.

REV. D

AD7249

–9–

Bipolar (ⴞ5 V) Configuration

The bipolar configuration for the AD7249, which gives an out-

put range of –5 V to +5 V, is achieved by connecting R

OFSA

OFSB

to V

REFIN

. The AD7249 must be operated from dual

supplies to achieve this output voltage range. Either offset binary

or twos complement coding may be selected. Figure 10 shows

the connection diagram for bipolar operation. An AD586 pro-

vides the reference voltage for the DAC but this could be pro-

vided by the on-chip reference by connecting REFOUT to

REFIN.

12-BIT

DAC A

12-BIT

DAC B

AD7249*

REFIN

OFSA

OUTA

–5V TO +5V

OFSB

OUTB

–5V TO +5V

BIN/COMPDGNDAGND

*ADDITIONAL PINS OMITTED FOR CLARITY.

OUT

AD586

Figure 10. Bipolar Configuration with External Reference

Bipolar Operation (Twos Complement Data Format)

The AD7249 is configured for twos complement data format

by connecting BIN/COMP (Pin 7) high. The analog output vs.

digital code is shown in Table II.

Table II. Twos Complement Bipolar Code Table

Input Data Word

MSB LSB Analog Output, V

OUT

XXXY 0111 1111 1111 +REFIN × (2047/2048)

XXXY 0000 0000 0001 +REFIN × (1/2048)

XXXY 0000 0000 0000 0 V

XXXY 1111 1111 1111 –REFIN × (1/2048)

XXXY 1000 0000 0001 –REFIN × (2047/2048)

XXXY 1000 0000 0000 –REFIN × (2048/2048) = –REFIN

X = Don’t Care.

Y = DAC Select Bit, 0 = DAC A, 1 = DAC B.

Note: 1 LSB = REFIN/2048.

Bipolar Operation (Offset Binary Data Format)

The AD7249 is configured for Offset Binary data format by

connecting BIN/COMP (Pin 7) low. The analog output vs.

digital code may be obtained by inverting the MSB in Table II.

APPLYING THE AD7249

Good printed circuit board layout is as important as the overall

circuit design itself in achieving high speed converter perfor-

mance. The AD7249 works on an LSB size of 2.44 mV for the

unipolar 0 V to 10 V range and the bipolar ±5 V range, when

using the unipolar 0 V to 5 V range the LSB size is 1.22 mV.

Therefore the designer must be conscious of minimizing noise in

both the converter itself and in the surrounding circuitry.

Switching mode power supplies are not recommended as switch-

ing spikes can feedthrough to the on-chip amplifier. Other causes of

concern are ground loops and feedthrough from microproces-

sors. These are factors which influence any high performance

converter, and proper printed circuit board layout which mini-

mizes these effects is essential to obtain high performance.

LAYOUT HINTS

Ensure that the layout has the digital and analog tracks sepa-

rated as much as possible. Take care not to run any digital track

alongside an analog signal track. Establish a single point analog

ground separate from the logic system ground. Place this star

ground as close as possible to the AD7249. Connect all analog

grounds to this star point and also connect the AD7249 DGND

pin to this point. Do not connect any other digital grounds to

this analog ground point. Low impedance analog and digital

power supply common returns are essential for low noise opera-

tion of high performance converters. To accomplish this track

widths should be kept a wide as possible and also the use of

ground planes minimizes impedance paths and also guards the

analog circuitry from digital noise.

NOISE

Keep the signal leads on the V

OUTA

and V

OUTB

signals and the

signal return leads to AGND as short as possible to minimize

noise coupling. In applications where this is not possible use a

shielded cable between the DAC outputs and their destination.

Reduce the ground circuit impedance as much as possible since

any potential difference in grounds between the DAC and its

destination device appears as an error voltage in series with the

DAC output.

Power Supply Decoupling

To achieve optimum performance when using the AD7249, the

and V

lines should be decoupled to AGND using 0.1 µF

capacitors. In noisy environments it is recommended that 10 µF

capacitors be connected in parallel with the 0.1 µF capacitors.

REV. D

–10–

AD7249

MICROPROCESSOR INTERFACING

Microprocessor interfacing to the AD7249 is via a serial bus

which uses standard protocol compatible with DSP processors

and microcontrollers. The communications channel requires a

three-wire interface consisting of a clock signal, a data signal

and a synchronization signal. The AD7249 requires a 16-bit

data word with data valid on the falling edge of SCLK. For all

the interfaces, the DAC update may be done automatically

when all the data is clocked in or it may be done under control

of LDAC.

Figures 11 to 15 show the AD7249 configured for interfacing to

a number of popular DSP processors and microcontrollers.

AD7249–ADSP-2101/ADSP-2102 Interface

Figure 11 shows a serial interface between the AD7249 and the

ADSP-2101/ADSP-2102 DSP processor. The ADSP-2101/

ADSP-2102 contains two serial ports and either port may be

used in the interface. The data transfer is initiated by TFS

going low. Data from the ADSP-2101/ADSP-2102 is clocked

into the AD7249 on the falling edge of SCLK. DB12 of the

16-bit serial data stream selects the DAC to be updated. Both

DACs can be updated by holding LDAC high while performing

two write cycles to the DAC. TFS must be taken high after

each 16 bit write cycle. LDAC is brought low at the end of the

second cycle and both DAC outputs are updated together. In

the interface shown the DAC is updated using an external timer

which generates an LDAC pulse. This could also be done using

a control or decoded address line from the processor. Alterna-

tively, if the LDAC input is hardwired low the output update

takes place automatically on the 16th falling edge of SCLK.

AD7249*

ADSP-2101/

ADSP-2102* LDAC

SCLK

SDIN

SYNC

SCLK

TFS

TIMER

*ADDITIONAL PINS OMITTED FOR CLARITY.

Figure 11. AD7249–ADSP-2101/ADSP-2102 Interface

AD7249–DSP56000 Interface

A serial interface between the AD7249 and the DSP56000 is

shown in Figure 12. The DSP56000 is configured for Normal

Mode Asynchronous operation with Gated Clock. It is also set

up for a 16-bit word with SCK and SC2 as outputs and the

FSL control bit set to a “0.” SCK is internally generated on the

DSP56000 and applied to the AD7249 SCLK input. Data from

the DSP56000 is valid on the falling edge of SCK. The SC2

output provides the framing pulse for valid data. This line must

be inverted before being applied to the SYNC input of the

AD7249.

AD7249*

DSP56000

LDAC

SCLK

SDIN

SYNC

SCK

STD

SC2

TIMER

*ADDITIONAL PINS OMITTED FOR CLARITY.

Figure 12. AD7249–DSP56000 Interface

In this interface an external LDAC pulse generated from an

external timer is used to update the outputs of the DACs. This

update can also be produced using a bit programmable control

line from the DSP56000.

AD7249–TMS32020 Interface

Figure 13 shows a serial interface between the AD7249 and the

TMS32020 DSP processor. In this interface, the CLKX and

FSX signals for the TMS32020 should be generated using

external clock/timer circuitry. The FSX pin of the TMS32020

must be configured as an input. Data from the TMS32020 is

valid on the falling edge of CLKX.

The clock/timer circuitry generates the LDAC signal for the

AD7249 to synchronize the update of the output with the serial

transmission. Alternatively, the automatic update mode may be

selected by connecting LDAC to DGND.

AD7249*

TMS32020

LDAC

SCLK

SDIN

SYNC

FSX

CLKX

CLOCK/

TIMER

*ADDITIONAL PINS OMITTED FOR CLARITY.

Figure 13. AD7249–TMS32020 Interface

REV. D

AD7249

–11–

AD7249–68HC11 Interface

Figure 14 shows a serial interface between the AD7249 and the

68HC11 microcontroller. SCK of the 68HC11 drives SCLK of

the AD7249 while the MOSI output drives the serial data line

of the AD7249. The SYNC signal is derived from a port line

(PC0 shown).

For correct operation of this interface, the 68HC11 should be

configured such that its CPOL bit is a 0 and its CPHA bit is a

1. When data is to be transmitted to the part, PC0 is taken low.

When the 68HC11 is configured like this, data on MOSI is

valid on the falling edge of SCK. The 68HC11 transmits its

serial data in 8-bit bytes with only eight falling clock edges

occurring in the transmit cycle. To load data to the AD7249,

PC0 is left low after the first eight bits are transferred and a sec-

ond byte of data is then transferred serially to the AD7249.

When the second serial transfer is complete, the PC0 line is

taken high.

Figure 14 shows the LDAC input of the AD7249 being driven

from another bit programmable port line (PC1). As a result,

both DACs can be updated simultaneously by taking LDAC

low after both DACs latches have updated.

AD7249*

68HC11*

LDAC

SCLK

SDIN

SYNCPC0

SCK

MOSI

*ADDITIONAL PINS OMITTED FOR CLARITY.

PC1

Figure 14. AD7249–68HC11 Interface

AD7249–87C51 Interface

A serial interface between the AD7249 and the 87C51 micro-

controller is shown in Figure 15. TXD of the 87C51 drives

SCLK of the AD7249 while RXD drives the serial data line of

the part. The SYNC signal is derived from the port line P3.3

and the LDAC line is driven port line P3.2.

The 87C51 provides the LSB of its SBUF register as the first

bit in the serial data stream. Therefore, the user will have to

ensure that the data in the SBUF register is arranged correctly

so that the don’t care bits are the first to be transmitted to the

AD7249 and the last bit to be sent is the LSB of the word to be

loaded to the AD7249. When data is to be transmitted to the

part, P3.3 is taken low. Data on RXD is valid on the falling

edge of TXD. The 87C51 transmits its serial data in 8-bit bytes

with only eight falling clock edges occurring in the transmit

cycle. To load data to the AD7249, P3.3 is left low after the

first eight bits are transferred, and a second byte of data is then

transferred serially to the AD7249 with DB12 used to select

the appropriate DAC register. When the second serial transfer

is complete, the P3.3 line is taken high and then taken low

again to start the loading sequence to the second DAC (see

timing diagram Figure 8).

Figure 15 shows the LDAC input of the AD7249 driven from

the bit programmable port line P3.2. As a result, both DAC

outputs can be updated simultaneously by taking the LDAC

line low following the completion of the write cycle to the sec-

ond DAC. Alternatively LDAC could be hardwired low and the

analog output will be updated on the sixteenth falling edge of

TXD after the SYNC signal for the DAC has gone low.

AD7249*

87C51*

LDAC

SCLK

SDIN

SYNCP3.3

TXD

RXD

*ADDITIONAL PINS OMITTED FOR CLARITY.

P3.2

Figure 15. AD7249–87C51 Interface

APPLICATIONS

OPTO-ISOLATED INTERFACE

In many process control type applications it is necessary to

provide an isolation barrier between the controller and the

unit being controlled. Opto-isolators can provide voltage

isolation in excess of 3 kΩ. The serial loading structure of the

AD7249 makes it ideal for opto-isolated interfaces as the num-

ber of interface lines is kept to a minimum.

Figure 16 shows a 2-channel isolated interface using the

AD7249.

The sequence of events to program the output channels is as

follows.

1. Take the SYNC line low.

2. Transmit the 16-bit word for DAC A (DB 12 of the 16-bit

data word selects the DAC, DB12 = 0 to select DAC A) and

bring the SYNC line high after the 16 bits have been trans-

mitted.

3. Bring SYNC line low again and transmit 16 bits for DAC B,

bring SYNC back high at end of transmission.

4. Pulse the LDAC line low. This updates both output chan-

nels simultaneously on the falling edge of LDAC.

REV. D

–12–

AD7249

DATA OUT

CLOCK OUT

SYNC OUT

CONTROL OUT

CONTROLLER

AD7249*

SDIN

SCLK

SYNC

LDAC

VOUTA

VOUTB

VDD

QUAD OPTO-COUPLER

*ADDITIONAL PINS OMITTED FOR CLARITY.

VOUTA

VOUTB

Figure 16. Opto-Isolated Interface

REV. D

AD7249

Rev. D | Page 13

OUTLINE DIMENSIONS

Figure 17. 16-Lead Plastic Dual In-Line Package [PDIP]

Narrow Body

(N-16)

Dimensions shown in inches and (millimeters)

Figure 18. 16-Lead Standard Small Outline Package [SOIC_W]

Wide Body

(RW-16)

Dimensions shown in millimeters and (inches)

CONTRO L LI NG DIME NS I ONS ARE I N I NCHE S ; MIL LI ME TER DI M E NS I ONS

(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR

REF ERENCE ON LY AND ARE NOT APPROPRIATE FOR USE IN DESIG N .

CORNER LEADS MAY BE CONF IG U RE D AS WHO LE OR HALF LEADS .

COMPL IANT TO JE DE C STANDARDS M S-001- AB

073106-B

0.02 2 ( 0.56)

0.01 8 ( 0.46)

0.01 4 ( 0.36)

0.15 0 ( 3.81)

0.13 0 ( 3.30)

0.115 (2.92)

0.07 0 ( 1.78)

0.06 0 ( 1.52)

0.04 5 ( 1.14)

0.10 0 ( 2.54)

BSC

0.800 (20.32)

0.790 (20.07)

0.780 (19.81)

0.210 (5.33)

MAX

SEATING

PLANE

0.015

(0.38)

MIN

0.005 (0.13)

MIN

0.280 (7.11)

0.250 (6.35)

0.240 (6.10)

0.060 (1.52)

MAX

0.430 (10.92)

MAX

0.01 4 ( 0.36)

0.01 0 ( 0.25)

0.00 8 ( 0.20)

0.32 5 ( 8.26)

0.31 0 ( 7.87)

0.30 0 ( 7.62)

0.015 (0. 38)

GAUGE

PLANE

0.19 5 ( 4.95)

0.13 0 ( 3.30)

0.115 (2.92)

CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS

(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR

REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.

COMPLIANT TO JEDEC STANDARDS MS-013-AA

10.50 (0.4134)

10.10 (0.3976)

0.30 (0.0118)

0.10 (0.0039)

2.65 (0.1043)

2.35 (0.0925)

10.65 (0.4193)

10.00 (0.3937)

7.60 (0.2992)

7.40 (0.2913)

0.75(0.0295)

0.25(0.0098)

45°

1.27 (0.0500)

0.40 (0.0157)

OPLANARITY

0.10 0.33 (0.0130)

0.20 (0.0079)

0.51 (0.0201)

0.31 (0.0122)

SEATING

PLANE

8°

0°

16 9

1.27 (0.0500)

BSC

03-27-2007-B

AD7249

Rev. D | Page 14

Figure 19. 16-Lead Ceramic Dual In-Line Package [CERDIP]

(Q-16)

Dimensions shown in inches and (millimeters)

ORDERING GUIDE

Model1 Temperature Range Relative Accuracy Package Description Package Option

AD7249AN –40°C to +85°C ±1 LSB 16-Lead PDIP N-16

AD7249ANZ –40°C to +85°C ±1 LSB 16-Lead PDIP N-16

AD7249BNZ –40°C to +85°C ±1/2 LSB 16-Lead PDIP N-16

AD7249AR –40°C to +85°C ±1 LSB 16-Lead SOIC_W RW-16

AD7249AR-REEL –40°C to +85°C ±1 LSB 16-Lead SOIC_W RW-16

AD7249ARZ –40°C to +85°C ±1 LSB 16-Lead SOIC_W RW-16

AD7249ARZ-REEL –40°C to +85°C ±1 LSB 16-Lead SOIC_W RW-16

AD7249BR –40°C to +85°C ±1/2 LSB 16-Lead SOIC_W RW-16

AD7249BR-REEL –40°C to +85°C ±1/2 LSB 16-Lead SOIC_W RW-16

AD7249BRZ –40°C to +85°C ±1/2 LSB 16-Lead SOIC_W RW-16

AD7249BRZ-REEL –40°C to +85°C ±1/2 LSB 16-Lead SOIC_W RW-16

AD7249SQ –55°C to +125°C ±1 LSB 16-Lead CERDIP Q-16

1 Z = RoHS Compliant Part.

REVISION HISTORY

10/13—Rev. C to Rev. D

Updated Outline Dimensions ....................................................... 13

Changes to Ordering Guide .......................................................... 14

6/00—Rev. B to Rev. C

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.

0.840 (21.34) MAX

15°

0°

0.320 (8.13)

0.290 (7.37)

0.015 (0.38)

0.008 (0.20)

.200 (5.08)

MAX

0.200 (5.08)

0.125 (3.18)

0.023 (0.58)

0.014 (0.36)

0.310 (7.87)

0.220 (5.59)

0.005 (0.13) MIN 0.098 (2.49) MAX

0.100 (2.54) BSC

PIN 1

916

SEATING

PLANE

0.150

(3.81)

MIN

0.070 (1.78)

0.030 (0.76)

0.060 (1.52)

0.015 (0.38)

registered trademarks are the property of their respective owners.

D00997-0-10/13(D)