AD5557 Analog Devices, AD5557 Datasheet - Page 12

• Manufacturer Part Number: AD5557
• Description: Dual Current Output, Parallel Input, 14-Bit Multiplying DACs with 4-Quadrant Resistors
• Manufacturer: Analog Devices

Specifications of AD5557

• Resolution (bits): 14bit
• 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

AD5547/AD5557
CIRCUIT OPERATION
DAC SECTION
The
output, 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
or 0 V to +V
to +18 V references. In addition to the precision conversion R
commonly found in current output DACs, there are three addi-
tional precision resistors for 4-quadrant bipolar applications.
The
ladders, which make up the 12/10 LSBs, respectively. Furthermore,
the 4 MSBs are decoded into 15 segments of resistor value 2R.
Figure 18 shows the architecture of the 16-bit AD5547. Each of
the 16 segments and the R-2R ladder carries an equally weighted
current of one-sixteenth of full scale. The feedback resistor R
and 4-quadrant resistor R
resistor, R1 and R2, equals 5 kΩ. In 4-quadrant operation, R1,
R2, and an external op amp work together to invert the reference
voltage and apply it to the V
connected as shown in Figure 2, the output can swing from
−V
REF
AD5547/AD5557
AD5547/AD5557
to +V
REF
REF
.
) and bipolar (±V
are 16-/14-bit, multiplying, current-
consist of two groups of precision R-2R
RCOM
V
OFS
REF
R1
have values of 10 kΩ. Each 4-quadrant
REF
5kΩ
5kΩ
R2
R1
Figure 18. 16-Bit
LDAC
input. With R
WR
REF
) output ranges from –18 V
80kΩ
15
2R
LDAC
WR
D15 D14
RA
40kΩ
80kΩ
RB
80kΩ
AD5547
R
2R
8
OFS
2R
40kΩ
80kΩ
80kΩ
and R
R
R
80kΩ
2R
2R
4
Equivalent R-2R DAC Circuit with Digital Section, One Channel Shown
2R
40kΩ
80kΩ
80kΩ
FB
R
R
ADDRESS DECODER
2R
2R
INPUT REGISTER
DAC REGISTER
REF
40kΩ
80kΩ
80kΩ
Rev. C | Page 12 of 20
R
FB
2R
R
2R
FB
80kΩ
40kΩ
80kΩ
R
2R
R
2R
40kΩ
80kΩ
80kΩ
R
2R
2R
The reference voltage inputs exhibit a constant input resistance
of 5 kΩ ± 20%. The impedance of I
dependent. External amplifier choice should take into account
the variation of the
feedback resistance in parallel with the DAC ladder resistance
dominates output voltage noise. To maintain good analog
performance, it is recommended that the power supply is
bypassed 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
inverting node of the op amp. A compensation capacitor, therefore,
may be needed between the I-to-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
the DAC switches. Note that the output precision degrades if
the operating voltage falls below the specified voltage. Users
should also avoid using switching regulators because device
power supply rejection degrades at higher frequencies.
80kΩ
40kΩ
R
2R
DD
4-BIT R2R
40kΩ
80kΩ
D0
power is used primarily by the internal logic to drive
R
2R
RS
RS
80kΩ
2R
80kΩ
2R
AD5547/AD5557
RS
10kΩ
4 MSB
15 SEGMENTS
8-BIT R2R
10kΩ
ROFS
RFB
IOUT
AGND
REF
OUT
output impedance. The
and R
, the DAC output, is code
FB
should match.
Data Sheet