EVAL-AD5405EB View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
EVAL-AD5405EB
Analog Devices
'EVAL-AD5405EB' PDF : 24 Pages View PDF
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 RFBA has a value of 2R. The
value of R is typically 10 kΩ (with a minimum of 8 kΩ and a
maximum of 13 kΩ). If IOUT1A and IOUT2A are kept at the same
potential, a constant current flows into each ladder leg,
regardless of digital input code. Therefore, the input resistance
presented at VREFA is always constant.
VREF A
R
R
R
2R 2R 2R
S1 S2 S3
2R 2R
S12
R
DAC DATA LATCHES
AND DRIVERS
RFB A
IOUT1A
IOUT 2A
Figure 31. Simplified Ladder Configuration
Access is provided to the VREF, RFB, IOUT1, and IOUT2 terminals of
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.
VDD
R1A
R1
RFB
2R
2R
R2A
R2
2R
R2_3A
R3
2R
R3A
AD5405
12-Bit DAC A
R
AGND
VREFA
RFBA
IOUT1A
IOUT2A
C1
A1
VOUT = 0V TO –VIN
GND
AGND
AGND
NOTES
1. SIMILAR CONFIGURATION FOR DAC B.
2. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED
IF A1 IS A HIGH SPEED AMPLIFIER.
Figure 32. Unipolar Operation
When an output amplifier is connected in unipolar mode, the
output voltage is given by
VOUT = − VREF × D 2n
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 VIN is an ac
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
Analog Output (V)
1111 1111 1111
−VREF (4,095/4,096)
1000 0000 0000
−VREF (2,048/4,096) = −VREF/2
0000 0000 0001
−VREF (1/4,096)
0000 0000 0000
−VREF (0/4,096) = 0
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.
VDD
R1A
R1
RFB
2R
2R
R2A
VIN
R2
2R
R2_3A
R3
2R
R3A
A1
AD5405
12-Bit DAC A
R
RFBA
IOUT1A
IOUT2A
C1
A1
AGND
VREFA
GND
AGND
AGND
NOTES
1. SIMILAR CONFIGURATION FOR DAC B.
2. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED
IF A1 IS A HIGH SPEED AMPLIFIER.
VOUT = –VIN TO +VIN
Figure 33. Bipolar Operation (4-Quadrant Multiplication)
When in bipolar mode, the output voltage is given by
VOUT = (VREF × D 2n −1 ) − VREF
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 VIN is an ac signal, the circuit performs 4-quadrant
multiplication.
Rev. B | Page 14 of 24
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