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AD5313R View Datasheet(PDF) - Analog Devices

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AD5313R Datasheet PDF : 28 Pages
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AD5313R
THEORY OF OPERATION
DIGITAL-TO-ANALOG CONVERTER (DAC)
The AD5313R is a dual 10-bit, serial input, voltage output DAC
with an internal reference. The part operates from supply voltages
of 2.7 V to 5.5 V. Data is written to the AD5313R in a 24-bit word
format via a 3-wire serial interface. The AD5313R incorporates a
power-on reset circuit to ensure that the DAC output powers up to
a known output state. The device also has a software power-down
mode that reduces the typical current consumption to 4 µA.
TRANSFER FUNCTION
The internal reference is on by default. To use an external
reference, only a nonreference option is available. Because the
input coding to the DAC is straight binary, the ideal output
voltage when using an external reference is given by
VOUT
= VREF
× Gain
D
 2N

where:
Gain is the output amplifier gain and is set to 1 by default. It can
be set to ×1 or ×2 using the gain select pin. When the GAIN pin
is tied to GND, both DAC outputs have a span from 0 V to VREF.
If the GAIN pin is tied to VLOGIC, both DACs output a span of
0 V to 2 × VREF.
D is the decimal equivalent of the binary code that is loaded to
the DAC register as follows: 0 to 1,024 for the 10-bit device.
N is the DAC resolution.
DAC ARCHITECTURE
The DAC architecture consists of a string DAC followed by an
output amplifier. Figure 39 shows a block diagram of the DAC
architecture.
VREF
2.5V
REF
INPUT
REGISTER
DAC
REGISTER
REF (+)
RESISTOR
STRING
REF (–)
VOUTX
GND
GAIN
(GAIN = 1 OR 2)
Figure 39. Single DAC Channel Architecture Block Diagram
The resistor string structure is shown in Figure 40. It is a string
of resistors, each of Value R. The code loaded to the DAC register
determines the node on the string where the voltage is to be tapped
off and fed into the output amplifier. The voltage is tapped off
Data Sheet
by closing one of the switches connecting the string to the
amplifier. Because it is a string of resistors, it is guaranteed
monotonic.
VREF
R
R
R
TO OUTPUT
AMPLIFIER
R
R
Figure 40. Resistor String Structure
Internal Reference
The AD5313R on-chip reference is on at power-up but can be
disabled via a write to a control register. See the Internal
Reference Setup section for details.
The AD5313R has a 2.5 V, 2 ppm/°C reference, giving a full-
scale output of 2.5 V or 5 V, depending on the state of the
GAIN pin. The internal reference associated with the device is
available at the VREF pin. This buffered reference is capable of
driving external loads of up to 10 mA.
Output Amplifiers
The output buffer amplifier can generate rail-to-rail voltages on
its output, which gives an output range of 0 V to VDD. The actual
range depends on the value of VREF, the GAIN pin, the offset
error, and the gain error. The GAIN pin selects the gain of the
output, as follows:
If the GAIN pin is tied to GND, both DAC outputs have
a gain of 1, and the output range is 0 V to VREF.
If the GAIN pin is tied to VLOGIC, both DAC outputs have
a gain of 2, and the output range is 0 V to 2 × VREF.
These amplifiers are capable of driving a load of 1 kΩ in parallel
with 2 nF to GND. The slew rate is 0.8 V/µs with a ¼ to ¾ scale
settling time of 5 µs.
Rev. 0 | Page 18 of 28
 

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