Analog Devices AD5629 Evaluation Board EVAL-AD5629RSDZ EVAL-AD5629RSDZ 数据表
产品代码
EVAL-AD5629RSDZ
Data Sheet
AD5629R/AD5669R
THEORY OF OPERATION
DIGITAL-TO-ANALOG CONVERTER (DAC) SECTION
The architecture consists of a string of DACs followed by an
output buffer amplifier. Each part includes an internal
1.25 V/2.5 V, 5 ppm/°C reference with an internal gain of 2.
Figure 48 and Figure 49 show block diagrams of the DAC
output buffer amplifier. Each part includes an internal
1.25 V/2.5 V, 5 ppm/°C reference with an internal gain of 2.
Figure 48 and Figure 49 show block diagrams of the DAC
architecture.
OUTPUT
AMPLIFIER
GAIN = ×2
AMPLIFIER
GAIN = ×2
DAC
REGISTER
REF (+)
V
REFIN
/V
REFOUT
V
OUT
REF (–)
RESISTOR
STRING
GND
INTERNAL
REFERENCE
1
1
CAN BE OVERDRIVEN
BY V
BY V
REFIN
/V
REFOUT
.
08819-
045
Figure 48. DAC Architecture for Internal Reference Configuration
REF
BUFFER
BUFFER
OUTPUT
AMPLIFIER
GAIN = ×2
AMPLIFIER
GAIN = ×2
V
REFIN
/V
REFOUT
GND
REF (+)
REF (–)
RESISTOR
STRING
V
OUT
08819-
046
R
R
Figure 49. DAC Architecture for External Reference Configuration
Because the input coding to the DAC is straight binary, the ideal
output voltage when using an external reference is given by
×
=
N
REFIN
OUT
D
V
V
2
The ideal output voltage when using the internal reference is
given by
×
×
=
N
REFOUT
OUT
D
V
V
2
2
where:
D = decimal equivalent of the binary code that is loaded to the
DAC register as follows:
0 to 4095 for
DAC register as follows:
0 to 4095 for
(12 bits).
(16 bits).
N = the DAC resolution.
RESISTOR STRING
The resistor string section is shown in Figure 50. It is simply a
string of resistors, each of value R. The 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. The
voltage is tapped off by closing one of the switches connecting
the string to the amplifier. Because it is a string of resistors, it
string of resistors, each of value R. The 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. The
voltage is tapped off by closing one of the switches connecting
the string to the amplifier. Because it is a string of resistors, it
is guaranteed monotonic.
TO OUTPUT
AMPLIFIER
AMPLIFIER
R
R
R
R
R
08819-
047
Figure 50. Resistor String
INTERNAL REFERENCE
have a 1.25 V,
5 ppm/°C reference, giving a full-scale output of 2.5 V or the
have a 2.5 V,
5 ppm/°C reference, working between a supply from 4.5 V to
5.5 V giving a full-scale output of 5 V. The on-board reference
is off at power-up, allowing the use of an external reference. The
internal reference is enabled via a write to the control register
5.5 V giving a full-scale output of 5 V. The on-board reference
is off at power-up, allowing the use of an external reference. The
internal reference is enabled via a write to the control register
REFOUT
pin. A buffer is required if the reference output is
used to drive external loads. When using the internal reference,
it is recommended that a 100 nF capacitor be placed between
it is recommended that a 100 nF capacitor be placed between
the reference output and GND for reference stability.
Individual channel power-down is not supported while using
Individual channel power-down is not supported while using
the internal reference.
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