DAC8565ICPWG4 Datasheet, PDF (25/49 Pages) Texas Instruments – 16-Bit, Quad Channel, Ultra-Low Glitch, Voltage Output

DAC8565
www.ti.com
SBAS411C – JUNE 2007 – REVISED MARCH 2011
THEORY OF OPERATION
DIGITAL-TO-ANALOG CONVERTER (DAC)
The DAC8565 architecture consists of a string DAC
followed by an output buffer amplifier. Figure 92
shows a block diagram of the DAC architecture.
code loaded into the DAC register determines at
which node on the string the voltage is tapped off to
be fed into the output amplifier by closing one of the
switches connecting the string to the amplifier. It is
monotonic because it is a string of resistors.
DAC
Register
V_REFH
50kW
62kW
REF(+)
Resistor String
REF(-)
V_REFL
50kW
V_OUTX
V_REF
R_DIVIDER
V_REF
2
R
Figure 92. DAC8565 Architecture
The input coding to the DAC8565 can be straight
binary or two's complement, so the ideal output
voltage is given by Equation 1.
R
To Output Amplifier
(2x Gain)
V_OUTX + 2
V_REFL ) (V_REFH * V_REFL)
D_IN
65536 (1)
where D_IN = decimal equivalent of the binary code
that is loaded to the DAC register; it can range from 0
to 65535. X represents channel A, B, C, or D.
DATA FORMAT
R
The data format can be straight binary or two’s
complement. Table 1 illustrates the differences
between USB (unsigned straight binary) and BTC
(binary two’s complement) data formats.
R
Table 1. USB and BTC Codes
USB CODE
FFFFh
8001h
8000h
7FFFh
0000h
BTC CODE
7FFFh
...
0001h
0000h
FFFFh
...
8000h
DESCRIPTION
+Full-Scale – 1LSB
Midscale + 1LSB
Midscale
Midscale – 1LSB
Zero Scale
RESISTOR STRING
The resistor string section is shown in Figure 93. It is
simply a string of resistors, each of value R. The
Figure 93. Resistor String
OUTPUT AMPLIFIER
The output buffer amplifier is capable of generating
rail-to-rail voltages on its output, giving an output
range of 0V to AV_DD. It is capable of driving a load of
2kΩ in parallel with 1000pF to GND. The source and
sink capabilities of the output amplifier can be seen in
the Typical Characteristics. The slew rate is 2.2V/μs,
with a full-scale settling time of 8μs with the output
unloaded.
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Product Folder Link(s): DAC8565
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