AD5405YCP-REEL7 Analog Devices, AD5405YCP-REEL7 Datasheet - Page 14

• Manufacturer Part Number: AD5405YCP-REEL7
• Description: Dual 12-Bit/ High Bandwidth/ Multiplying DAC with 4-Quadrant Resistors and Parallel Interface
• Manufacturer: Analog Devices

AD5405
GENERAL DESCRIPTION
DAC SECTION
The AD5405 is a 12-bit, dual-channel, current-output DAC
consisting of a standard inverting R-2R ladder configuration.
Figure 31 shows a simplified diagram for a single channel of the
AD5405. The feedback resistor R
of R is typically 10 kΩ (minimum 8 kΩ and maximum 12 kΩ).
If I
current flows in each ladder leg, regardless of digital input code.
Thus, the input resistance presented at V
Access is provided to the V
each DAC, making the device extremely versatile and allowing
it to be configured in several different operating modes, such as
for unipolar output, bipolar output, or single-supply mode.
CIRCUIT OPERATION
Unipolar Mode
Using a single op amp, this DAC can easily be configured to
provide 2-quadrant multiplying operation or a unipolar output
voltage swing, as shown in Figure 32.
AGND
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, and n is the resolution of the DAC.
V
R2_3A
D =
OUT
R3A
R2A
OUT
1A and I
NOTES
1. SIMILAR CONFIGURATION FOR DAC B
2. C1 PHASE COMPENSATION (1pF–2pF) MAY BE REQUIRED
0 to
V
=
IF A1 IS A HIGH SPEED AMPLIFIER.
V
REF A
DD
−
V
R2
2R
R3
2R
REF
4095
D
A
Figure 31. Simplified Ladder Configuration
R1A
OUT
2
DAC DATA LATCHES
n
2R
S1
2A are kept at the same potential, a constant
×
R
AND DRIVERS
V
Figure 32. Unipolar Operation
R1
2R
12-Bit DAC A
REF
AD5405
2R
S2
R
R
R
REF
2R
FB
2R
S3
, R
R
FB
AGND
GND
FB
, I
has a value of 2R. The value
I
I
OUT
OUT
2R
S12
OUT
R
FB
1A
2A
1, and I
A
REF
2R
AGND
is always constant.
2R
C1
OUT
A1
R
I
I
OUT 2A
2 terminals of
OUT1A
FB
V
OUT
A
= 0V TO –V
Rev. 0 | Page 14 of 24
IN
With a fixed 10 V reference, the circuit shown in Figure 32 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
expected output voltage for unipolar operation.
Table 5. Unipolar Code Table
Digital Input
1111 1111
1000 0000
0000 0001
0000 0000
Bipolar Operation
In some applications, it may be necessary to generate full
4-quadrant multiplying operation or a bipolar output swing.
This can be easily accomplished by using another external
amplifier, as shown in Figure 33.
When in bipolar mode, the output voltage is given by
where D is the fractional representation of the digital word
loaded to the DAC, in the range of 0 to 4095, and n is the
number of bits. When V
4-quadrant multiplication.
Table 6 shows the relationship between the digital code and the
expected output voltage for bipolar operation.
Table 6. Bipolar Code Table
Digital Input
1111 1111
1000 0000
0000 0001
0000 0000
AGND
V
V
OUT
A1
IN
R2_3A
Figure 33. Bipolar Operation (4-Quadrant Multiplication)
=
R3A
R2A
NOTES
1. SIMILAR CONFIGURATION FOR DAC B
2. C1 PHASE COMPENSATION (1pF–2pF) MAY BE REQUIRED
V
IF A1 IS A HIGH SPEED AMPLIFIER.
REF
V
DD
V
R2
2R
R3
2R
×
REF
D
A
R1A
2
n
−1
Analog Output (V)
−V
−V
−V
−V
R1
2R
12-Bit DAC A
×
IN
AD5405
REF
REF
REF
REF
V
is an ac signal, the circuit performs
R
REF
(4095/4096)
(2048/4096) = −V
(1/4096)
(0/4096) = 0
Analog Output (V)
+V
0
−V
−V
R
2R
FB
REF
REF
REF
GND
AGND
(2047/2048)
(2047/2048)
(2048/2048)
I
I
OUT
OUT
R
FB
1A
2A
A
AGND
C1
REF
A1
/2
V
OUT
IN
= –V
is an ac
IN
TO +V
IN