Serial Input,
14-Bit/16-Bit DAC
AD7849
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©1995–2011 Analog Devices, Inc. All rights reserved.
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 controls
PC analog I/O boards
Instrumentation
FUNCTIONAL BLOCK DIAGRAM
DD
CC
R
R
R
R
R
AD7849
R
OFS
RST IN
V
OUT
AGND
RST OUT
G1
G2
SDIN SCLK
SYNC CLR
BIN/
COMP
DCEN SDOUT
LDAC
V
SS
DGND
DAC
LATCH
10/
12
10/
12
10-BIT/
12-BIT
DAC
A1
A2
16-SEGMENT
SWITCH MATRIX
4
REF+
V
REF–
A3
LOGIC
CIRCUITRY
VOLTAGE
MONITOR
INPUT
LATCH
INPUT SHIFT REGISTER/
CONTROL LOGIC
01008-001
Figure 1.
GENERAL DESCRIPTION
The AD7849 is a 14-bit/16-bit serial input multiplying digital-
to-analog converter (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 from 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 (
RSTIN
) control input. For instance, if
the
RSTIN
input is driven from a battery supervisor chip, then
at power-off or during a brown out, the
RSTIN
input is driven
low to open G1 and close G2. The DAC must be reloaded, with
RSTIN
high, to reenable the output. Conversely, the on-chip
voltage detector output (
RSTOUT
) is also available to the user
to control other parts of the system.
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 daisy-chain enable (DCEN) input controls
this function.
The
BIN
/COMP pin sets the DAC coding; with
BIN
/COMP set
to 0, the coding is straight binary; and with
BIN
/COMP set to 1,
the coding is twos 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 PDIP package and a 20-lead SOIC
package.
