REV. B

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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.

a

Serial Input,

14-Bit/16-Bit DAC

AD7849*

FEATURES

14-Bit/16-Bit Multiplying DAC

Guaranteed Monotonicity

Output Control on Power-Up and Power-Down

Internal or External Control

Versatile Serial Interface

DAC Clears to 0 V in Both Unipolar and Bipolar Output

Ranges

APPLICATIONS

Industrial Process Control

PC Analog I/O Boards

Instrumentation

GENERAL DESCRIPTION

The AD7849 is a 14-bit/16-bit serial input multiplying DAC.

The DAC architecture ensures excellent differential linearity

performance, and monotonicity is guaranteed to 14 bits for the

A grade and to 16 bits for all other grades over the specified

temperature ranges.

During power-up and power-down sequences (when the supply

impedance path. To prevent the output of A3 being shorted to

0 V during this time, transmission gate G1 is also opened.

These conditions are maintained until the power supplies

stabilize and a valid word is written to the DAC register. At this

time, G2 opens and G1 closes. Both transmission gates are also

externally controllable via the Reset In (

RST IN) control input.

For instance, if the

RST IN input is driven from a battery super-

visor chip, then on power-off or during a brown out, the

RST

IN input will be driven low to open G1 and close G2. The DAC

must be reloaded, with

RST IN high, to re-enable the output.

Conversely, the on-chip voltage detector output (

RST OUT) is

also available to the user to control other parts of the system.

FUNCTIONAL BLOCK DIAGRAM

R

R

R

R

R

AD7849

RST IN

AGND

RST OUT

G1

G2

SDIN SCLK

SYNC CLR BIN/

COMP

DCEN SDOUT

DGND

DAC

LATCH

10/

12

10/

12

10-BIT/

12-BIT

DAC

A1

A2

16-

SEG-

MENT

SWITCH

MATRIX

4

A3

LOGIC

CIRCUITRY

VOLTAGE

MONITOR

INPUT

LATCH

INPUT SHIFT REGISTER/

CONTROL LOGIC

The AD7849 has a versatile serial interface structure and can be

controlled over three lines to facilitate opto-isolator applications.

SDOUT is the output of the on-chip shift register and can be

used in a daisy-chain fashion to program devices in the multi-

channel system. The DCEN (Daisy Chain Enable) input con-

trols this function.

The

BIN/COMP pin sets the DAC coding; with BIN/COMP

set to 0, the coding is straight binary; and with it set to 1, the

coding is 2s complement. This allows the user to reset the DAC

to 0 V in both the unipolar and bipolar output ranges.

The part is available in a 20-lead DIP and 20-lead SOIC package.

*Protected by U.S. Patent No. 5,319,371.

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., 2000