EVAL-AD5429EBZ Analog Devices Inc, EVAL-AD5429EBZ Datasheet - Page 15

• Manufacturer Part Number: EVAL-AD5429EBZ
• Description: BOARD EVALUATION FOR AD5429
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5429EBZ

• Number Of Dac's: 2
• Number Of Bits: 8
• Outputs And Type: 2, Single Ended
• Sampling Rate (per Second): 2.47M
• Data Interface: Serial
• Settling Time: 30ns
• Dac Type: Current
• Voltage Supply Source: Single
• Operating Temperature: -40°C ~ 125°C
• Utilized Ic / Part: AD5429
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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. C | Page 15 of 32
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