Serial Input,
14-Bit/16-Bit DAC
AD7849
FEATURES
FUNCTIONAL BLOCK DIAGRAM
VDD
R
ROFS
R
R
APPLICATIONS
Industrial process controls
PC analog I/O boards
Instrumentation
VCC
VREF+
16-SEGMENT
SWITCH MATRIX
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
RST IN
G1
10-BIT/
12-BIT
DAC
10/
12
A2
R
VREF–
R
A1
VOUT
A3
LOGIC
CIRCUITRY
G2
DAC
LATCH
4
10/
12
AD7849
VOLTAGE
MONITOR
INPUT
LATCH
AGND
RST OUT
DGND
SDIN SCLK SYNC CLR BIN/ DCEN SDOUT LDAC VSS
COMP
01008-001
INPUT SHIFT REGISTER/
CONTROL LOGIC
Figure 1.
GENERAL DESCRIPTION
The AD7849 is a 14-bit/16-bit serial input multiplying digitalto-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.
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 multichannel 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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