AD5405 Analog Devices, AD5405 Datasheet - Page 14

• Manufacturer Part Number: AD5405
• Description: Dual 12-Bit, High Bandwidth, Multiplying DAC with 4 Quadrant Resistors and Parallel Interface
• Manufacturer: Analog Devices

Specifications of AD5405

• Resolution (bits): 12bit
• Dac Update Rate: 21.3MSPS
• Dac Settling Time: 80ns
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Par

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
value of R is typically 10 kΩ (with a minimum of 8 kΩ and a
maximum of 13 kΩ). If I
potential, a constant current flows into each ladder leg,
regardless of digital input code. Therefore, the input resistance
presented at V
Access is provided to the V
the DAC, making the device extremely versatile and allowing it
to be configured for several operating modes, such as 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
R2_3A
R3A
R2A
NOTES
1. SIMILAR CONFIGURATION FOR DAC B.
2. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED
V
IF A1 IS A HIGH SPEED AMPLIFIER.
V
REF A
DD
V
R2
2R
R3
2R
REF
A
REF
Figure 31. Simplified Ladder Configuration
R1A
DAC DATA LATCHES
A is always constant.
2R
S1
R
AND DRIVERS
Figure 32. Unipolar Operation
R1
2R
12-Bit DAC A
AD5405
2R
S2
R
OUT
R
R
REF
2R
1A and I
FB
2R
S3
, R
R
FB
AGND
GND
FB
, I
A has a value of 2R. The
I
I
2R
S12
OUT
OUT
OUT
OUT
R
FB
1A
2A
1, and I
2A are kept at the same
A
2R
AGND
R
C1
OUT
A1
R
I
I
OUT 2A
OUT1A
2 terminals of
FB
V
A
OUT
= 0V TO –V
Rev. B | Page 14 of 24
IN
When an output amplifier is connected in unipolar mode, the
output voltage is given by
where:
D is the fractional representation, in the range of 0 to 4,095, of
the digital word loaded to the DAC.
n is the resolution of the DAC.
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 the
expected output voltage for unipolar operation.
Table 5. Unipolar Code
Digital Input
1111 1111 1111
1000 0000 0000
0000 0000 0001
0000 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, in the range of 0 to 4,095, of
the digital word loaded to the DAC.
n is the number of bits.
When V
multiplication.
AGND
V
A1
IN
V
V
OUT
OUT
R2_3A
Figure 33. Bipolar Operation (4-Quadrant Multiplication)
IN
R3A
R2A
NOTES
1. SIMILAR CONFIGURATION FOR DAC B.
2. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED
is an ac signal, the circuit performs 4-quadrant
=
IF A1 IS A HIGH SPEED AMPLIFIER.
=
(
−
V
V
DD
V
V
R2
2R
R3
2R
REF
REF
REF
A
R1A
×
×
D
D
Analog Output (V)
−V
−V
−V
−V
R1
2R
2
12-Bit DAC A
2
AD5405
n
REF
REF
REF
REF
n
−
1
R
(4,095/4,096)
(2,048/4,096) = −V
(1/4,096)
(0/4,096) = 0
)
R
2R
FB
−
V
REF
GND
AGND
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