a
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
V
REF+
R
A1
16-
SEG-
MENT
SWITCH
MATRIX
Serial Input,
14-Bit/16-Bit DAC
AD7849*
FUNCTIONAL BLOCK DIAGRAM
V
DD
V
CC
R
R
OFS
R
G1
10-BIT/
12-BIT
DAC
10/
12
R
V
REF–
4
A2
DAC
LATCH
10/
12
VOLTAGE
MONITOR
AGND
RST OUT
A3
V
OUT
RST IN
R
LOGIC
CIRCUITRY
G2
AD7849
INPUT
LATCH
INPUT SHIFT REGISTER/
CONTROL LOGIC
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
voltages are changing), the V
OUT
pin is clamped to 0 V via a low
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.
DGND
SDIN SCLK
SYNC CLR BIN/
DCEN SDOUT
LDAC
V
SS
COMP
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.
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., 2000
AD [ ANALOG DEVICES ]
