AD5546 Analog Devices, AD5546 Datasheet - Page 10

• Manufacturer Part Number: AD5546
• Description: Current-Output Parallel-Input, 16-Bit Digital-to-Analog Converter
• Manufacturer: Analog Devices

Specifications of AD5546

• Resolution (bits): 16bit
• Dac Update Rate: 2MSPS
• Dac Settling Time: 500ns
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Par

AD5546/AD5556
CIRCUIT OPERATION
DIGITAL-TO-ANALOG (DAC) CONVERTER SECTION
The AD5546/AD5556 are 16-/14-bit multiplying, current out-
put, and parallel input DACs. The devices operate from a single
2.7 V to 5.5 V supply and provide both unipolar 0 V to –V
0 V to +V
+18 V reference. In addition to the precision conversion R
commonly found in current output DACs, there are three addi-
tional precision resistors for four-quadrant bipolar applications.
The AD5546/AD5556 consist of two groups of precision R-2R
ladders, which make up the 12/10 LSBs, respectively. Further-
more, the four MSBs are decoded into 15 segments of resistor
value 2R. Figure 17 shows the architecture of the 16-bit AD5546.
Each of the 16 segments in the R-2R ladder carries an equally
weighted current of one-sixteenth of full scale. The feedback
resistor, R
kΩ. Each four-quadrant resistor, R1 and R2, equals 5 kΩ. In
four-quadrant operation, R1, R2, and an external op amp work
together to invert the reference voltage and apply it to the REF
input. With R
output can swing from –V
The reference voltage inputs exhibit a constant input resistance
of 5 kΩ ±20%. The DAC output, I
dent. External amplifier choice should take into account the
REF
FB
, and four-quadrant resistor, R
, and bipolar ±V
OFS
and R
FB
R
connected as shown in Figure 2, the
REF
COM
R1
REF
REF
5kΩ
5kΩ
to +V
R2
R1
LDAC
output ranges from a –18 V to
WR
OUT
REF
, impedance is code depen-
.
80kΩ
Figure 17. 16-Bit AD5546 Equivalent R-2R DAC Circuit with Digital Section
16
2R
LDAC
WR
D15 D14
OFS
RA
40kΩ
80kΩ
RB
, have values of 10
80kΩ
R
2R
8
2R
80kΩ
40kΩ
80kΩ
R
80kΩ
R
2R
2R
4
2R
40kΩ
80kΩ
80kΩ
R
R
ADDRESS DECODER
2R
2R
INPUT REGISTER
FB
REF
DAC REGISTER
Rev. D | Page 10 of 20
40kΩ
80kΩ
, or
80kΩ
R
2R
R
2R
40kΩ
80kΩ
80kΩ
R
2R
R
2R
80kΩ
40kΩ
80kΩ
R
2R
variation of the AD5546/AD5556 output impedance. The
feedback resistance in parallel with the DAC ladder resistance
dominates output voltage noise. To maintain good analog
performance, it is recommended to bypass the power supply
with a 0.01 μF to 0.1 μF ceramic or chip capacitor in parallel
with a 1 μF tantalum capacitor. Also, to minimize gain error,
PCB metal traces between V
Every code change of the DAC corresponds to a step function;
gain peaking at each output step may occur if the op amp has
limited GBP and excessive parasitic capacitance present at the
op amp inverting node. A compensation capacitor, therefore,
may be needed between the I-V op amp inverting and output
nodes to smooth the step transition. Such a compensation
capacitor should be found empirically, but a 20 pF capacitor is
generally adequate for the compensation.
The V
drive the DAC switches. Note that the output precision
degrades if the operating voltage falls below the specified
voltage. The user should also avoid using switching regulators
because device power supply rejection degrades at higher
frequencies.
2R
40kΩ
80kΩ
R
2R
DD
4-BIT R–2R
power is used primarily by the internal logic and to
80kΩ
40kΩ
D0
R
2R
RS
RS
80kΩ
2R
80kΩ
2R
RS
4 MSB
15 SEGMENTS
8-BIT R–2R
10kΩ
REF
and R
10kΩ
R
R
I
GND
OFS
FB
OUT
FB
should match.
Data Sheet