AD7849_15 Datasheet, PDF (1/20 Pages) Analog Devices – Serial Input, 14-Bit/16-Bit DAC

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
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 VOUT 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.
Serial Input,
14-Bit/16-Bit DAC
AD7849
V_REF+
R
R
R
V_REF–
FUNCTIONAL BLOCK DIAGRAM
V_DD
V_CC
R
A1
R
G1
10-BIT/
12-BIT
DAC
10/
12
A3
G2
LOGIC
CIRCUITRY
A2
DAC
LATCH
4
10/
12
VOLTAGE
MONITOR
AD7849
INPUT
LATCH
INPUT SHIFT REGISTER/
CONTROL LOGIC
R_OFS
RST IN
V_OUT
AGND
RST OUT
DGND SDIN SCLK SYNC CLR BIN/ DCEN SDOUT LDAC V_SS
COMP
Figure 1.
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.
Rev. C
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