AD7249 Datasheet PDF ( Pinout ) - LC2MOS Dual 12-Bit Serial DACPORT

AD7249 Datasheet PDF - Analog Devices

Part Number	*AD7249*
Description	LC2MOS Dual 12-Bit Serial DACPORT
Manufacturers	Analog Devices
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LC2MOS

Dual 12-Bit Serial DACPORT®

AD7249

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

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.

REFOUT

FUNCTIONAL BLOCK DIAGRAM

VDD

VSS

AD7249

ROFSA

REFIN

AGND

DGND

12-BIT

DAC A

12-BIT

DAC B

INPUT SHIFT REGISTER

VOUTA

ROFSB

VOUTB

SCLK SDIN SYNC BIN/COMP CLR LDAC

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

(LC2MOS), 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

DACPORT is a registered trademark of Analog Devices, Inc.

REV. C

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

AD7249

TERMINOLOGY

Bipolar Zero Error

Bipolar Zero Error is the voltage measured at VOUT 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 VOUT 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 VOUT 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 (VSS) 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.

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 VOUT

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.

ROFS

R RRRR

VOUT

2R 2R 2R

OUTPUT

VOLTAGE

REFIN*

AGND

SHOWN FOR ALL 1s

ON DAC

*BUFFERED REFIN VOLTAGE

Figure 2. D/A Simplified Circuit Diagram

NEGATIVE

OFFSET

DAC CODE

Figure 1. Effect of Negative Offset (Single Supply)

REV. C

–5–

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