ad5669rbruz Analog Devices, Inc., ad5669rbruz Datasheet - Page 23

• Manufacturer Part Number: ad5669rbruz
• Description: Octal, 12-/16-bit Dac, I C , 5ppm/
• Manufacturer: Analog Devices, Inc.

AD5629R/AD5669R
THEORY OF OPERATION
D/A SECTION
The AD5629R/AD5669R are fabricated on a CMOS process.
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
71 shows a block diagram of the DAC architecture.
Because the input coding to the DAC is straight binary, the ideal
output voltage when using an external reference is given by
The ideal output voltage when using the internal reference is
given by
where:
D = decimal equivalent of the binary code that is loaded to the
DAC register.
N = the DAC resolution.
RESISTOR STRING
The resistor string section is shown in Figure 72. 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
0 to 4095 for AD5629R (12 bits).
0 to 65,535 for AD5669R (16 bits).
V
V
Figure 71. DAC Architecture for external reference configuration
Figure 70 DAC Architecture for internal reference configuration
OUT
OUT
=
=
V
2
REFIN
×
V
REFOUT
⎛ ×
⎜
⎝
2
D
N
⎛ ×
⎜
⎝
⎞
⎟
⎠
2
D
N
⎞
⎟
⎠
Rev. PrA | Page 23 of 33
the string to the amplifier. Because it is a string of resistors, it is
guaranteed monotonic.
INTERNAL REFERENCE
The AD5629R/AD5669R have an on-chip reference with an
internal gain of 2. The AD5629R/AD5669R have a 1.25 V, 5
ppm/°C reference, giving a full-scale output of 2.5 V; or a 2.5 V, 5
ppm/°C reference, which will only work from 4.5 to 5.5Vgiving
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
(see Table 8).
The internal reference associated with each part is available at
the V
used to drive external loads. When using the internal reference,
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
the internal reference.
REFOUT
pin. A buffer is required if the reference output is
R
R
R
R
R
Preliminary Technical Data
Figure 72. Resistor String
TO OUTPUT
AMPLIFIER