AD5547/AD5557 Data Sheet
Rev. D | Page 18 of 20
REFERENCE SELECTION
When selecting a reference for use with the AD55xx series of
current output DACs, pay attention to the output voltage,
temperature coefficient specification of the reference. Choosing
a precision reference with a low output temperature coefficient
minimizes error sources. Table 10 lists some of the references
available from Analog Devices, Inc., that are suitable for use
with this range of current output DACs.
AMPLIFIER SELECTION
The primary requirement for the current-steering mode is an
amplifier with low input bias currents and low input offset voltage.
Because of the code-dependent output resistance of the DAC,
the input offset voltage of an op amp is multiplied by the variable
gain of the circuit. A change in this noise gain between two
adjacent digital fractions produces a step change in the output
voltage due to the amplifier’s input offset voltage. This output
voltage change is superimposed upon the desired change in output
between the two codes and gives rise to a differential linearity error,
which, if large enough, can cause the DAC to be nonmonotonic.
The input bias current of an op amp also generates an offset at
the voltage output because of the bias current flowing in the
feedback resistor, R
FB
.
Common-mode rejection of the op amp is important in voltage-
switching circuits because it produces a code-dependent error
at the voltage output of the circuit.
Provided that the DAC switches are driven from true wideband
low impedance sources (V
IN
and AGND), they settle quickly.
Consequently, the slew rate and settling time of a voltage-switching
DAC circuit is determined largely by the output op amp. To obtain
minimum settling time in this configuration, minimize capacitance
at the V
REF
node (the voltage output node in this application) of
the DAC. This is done by using low input capacitance buffer
amplifiers and careful board design.
Analog Devices offers a wide range of amplifiers for both precision
dc and ac applications, as listed in Table 11 and Table 12.
Table 10. Suitable Analog Devices Precision References
Part No. Output Voltage (V) Initial Tolerance (%)
Drift (ppm/°C) I
(mA) Output Noise (µV p-p) Package(s)
ADR01 10 0.05 3 1 20 SOIC-8
ADR01 10 0.05 9 1 20 TSOT-5, SC70-5
ADR02 5.0 0.06 3 1 10 SOIC-8
ADR02 5.0 0.06 9 1 10 TSOT-5, SC70-5
ADR03 2.5 0.1 3 1 6 SOIC-8
ADR06 3.0 0.1 3 1 10 SOIC-8
ADR06 3.0 0.1 9 1 10 TSOT-5, SC70-5
ADR420 2.048 0.05 3 0.5 1.75 SOIC-8, MSOP-8
ADR421 2.50 0.04 3 0.5 1.75 SOIC-8, MSOP-8
ADR425 5.00 0.04 3 0.5 3.4 SOIC-8, MSOP-8
ADR431 2.500 0.04 3 0.8 3.5 SOIC-8, MSOP-8
ADR435 5.000 0.04 3 0.8 8 SOIC-8, MSOP-8
ADR391 2.5 0.16 9 0.12 5 TSOT-5
ADR395 5.0 0.10 9 0.12 8 TSOT-5
Table 11. Suitable Analog Devices Precision Op Amps
Part No. Supply Voltage (V)
V
OS
Maximum
(µV)
I
B
Maximum
(nA)
0.1 Hz to 10 Hz
Noise (µV p-p) Supply Current (µA) Package(s)
OP97 ±2 to ±20 25 0.1 0.5 600 SOIC-8 , PDIP-8
OP1177 ±2.5 to ±15 60 2 0.4 500 MSOP-8, SOIC-8
AD8675 ±5 to ±18 75 2 0.1 2300 MSOP-8, SOIC-8
AD8671 ±5 to ±15 75 12 0.077 3000 MSOP-8, SOIC-8
ADA4004-1 ±5 to ±15 125 90 0.1 2000 SOIC-8, SOT-23-5
AD8603 1.8 to 5 50 0.001 2.3 40 TSOT-5
AD8607 1.8 to 5 50 0.001 2.3 40 MSOP-8, SOIC-8
AD8605 2.7 to 5 65 0.001 2.3 1000 WLCSP-5, SOT-23-5
AD8615 2.7 to 5 65 0.001 2.4 2000 TSOT-5
AD8616 2.7 to 5 65 0.001 2.4 2000 MSOP-8, SOIC-8
