AD5449 Analog Devices, AD5449 Datasheet - Page 15
AD5449
Manufacturer Part Number
AD5449
Description
Dual 12-Bit, High Bandwidth Multiplying DAC with Serial Interface
Manufacturer
Analog Devices
Datasheet
1.AD5429.pdf
(28 pages)
Specifications of AD5449
Resolution (bits)
12bit
Dac Update Rate
2.47MSPS
Dac Settling Time
80ns
Max Pos Supply (v)
+5.5V
Single-supply
Yes
Dac Type
Current Out
Dac Input Format
Ser,SPI
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THEORY OF OPERATION
DIGITAL-TO-ANALOG CONVERTER
The AD5429/AD5439/AD5449 are 8-, 10-, and 12-bit, dual-
channel, current output DACs consisting of a standard inverting
R-2R ladder configuration. Figure 37 shows a simplified diagram
for a single channel of the AD5449. The feedback resistor, R
has a value of R. The value of R is typically 10 kΩ (with a
minimum of 8 kΩ and a maximum of 12 kΩ). If I
I
into each ladder leg, regardless of digital input code. Therefore,
the input resistance presented at V
Access is provided to the V
nals of the DACs, making the devices extremely versatile and
allowing them to be configured in several operating modes, such
as unipolar mode, bipolar output mode, or single-supply mode.
CIRCUIT OPERATION
Unipolar Mode
Using a single op amp, these devices can easily be configured to
provide 2-quadrant multiplying operation or a unipolar output
voltage swing, as shown in Figure 38.
OUT
V
2A are kept at the same potential, a constant current flows
REF
A
2R
S1
R
DAC DATA LATCHES
AND DRIVERS
2R
Figure 37. Simplified Ladder
S2
R
2R
S3
REF
x, R
R
FB
REF
x, I
A is always constant.
V
2R
S12
OUT
REF
1x, and I
NOTES
1. R1 AND R2 USED ONLY IF GAIN ADJUSTMENT IS REQUIRED.
2. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED
3. DAC B OMITTED FOR CLARITY.
R1
2R
IF A1 IS A HIGH SPEED AMPLIFIER.
R
MICROCONTROLLER
V
SYNC
OUT
OUT
REF
1A and
x
2x termi-
R
I
I
OUT
OUT
SCLK
FB
AD5429/
AD5439/
AD5449
A
Figure 38. Unipolar Operation
1A
2A
V
V
DD
DD
SDIN
FB
Rev. D | Page 15 of 28
A,
GND
R
FB
I
I
OUT
OUT
A
1A
2A
R2
When an output amplifier is connected in unipolar mode, the
output voltage is given by
where:
D is the fractional representation of the digital word loaded to
the DAC.
n is the number of bits.
With a fixed 10 V reference, the circuit shown in Figure 38 gives
a unipolar 0 V to −10 V output voltage swing. When V
signal, the circuit performs 2-quadrant multiplication.
Table 5 shows the relationship between digital code and the
expected output voltage for unipolar operation using the 8-bit
AD5429 DAC.
Table 5. Unipolar Code Table
Digital Input
1111 1111
1000 0000
0000 0001
0000 0000
AGND
D = 0 to 255 (AD5429)
C1
V
= 0 to 1023 (AD5439)
= 0 to 4095 (AD5449)
OUT
A1
V
=
OUT
−
V
= 0V TO –V
REF
×
D
REF
2 /
AD5429/AD5439/AD5449
Analog Output (V)
−V
−V
−V
−V
n
REF
REF
REF
REF
(128/256) = −V
(255/256)
(1/256)
(0/256) = 0
REF
/2
IN
is an ac