AD5757 Analog Devices, AD5757 Datasheet - Page 40

• Manufacturer Part Number: AD5757
• Description: Quad Channel, 16-Bit, Serial Input, 4-20mA Output DAC, Dynamic Power Control, HART Connectivity
• Manufacturer: Analog Devices

Specifications of AD5757

• Resolution (bits): 16bit
• Dac Update Rate: 60kSPS
• Dac Settling Time: 15µs
• Max Pos Supply (v): +33V
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: SPI

AD5757
APPLICATIONS INFORMATION
CURRENT OUTPUT MODE WITH INTERNAL R
When using the internal R
the output is significantly affected by how many other channels
using the internal R
these channels. The internal R
for all channels enabled with the internal R
outputting the same code.
For every channel enabled with the internal R
decreases. For example, with one current output enabled using
the internal R
decreases proportionally as more current channels are enabled;
the offset error is 0.056% FSR on each of two channels, 0.029%
on each of three channels, and 0.01% on each of four channels.
Similarly, the dc crosstalk when using the internal R
tional to the number of current output channels enabled with
the internal R
0x8000 and one channel going from zero to full scale, the dc
crosstalk is −0.011% FSR. With two channels going from zero to
full scale, it is −0.019% FSR, and with all three other channels
going from zero to full scale, it is −0.025% FSR.
For the full-scale error measurement in Table 1, all channels are
at 0xFFFF. This means that, as any channel goes to zero scale,
the full-scale error increases due to the dc crosstalk. For example,
with the measured channel at 0xFFFF and three channels at
zero scale, the full-scale error is 0.025%. Similarly, if only one
channel is enabled in current output mode with the internal
R
PRECISION VOLTAGE REFERENCE SELECTION
To achieve the optimum performance from the AD5757 over its
full operating temperature range, a precision voltage reference
must be used. Thought should be given to the selection of a
precision voltage reference. The voltage applied to the reference
inputs is used to provide a buffered reference for the DAC cores.
Therefore, any error in the voltage reference is reflected in the
outputs of the device.
Table 34. Recommended Precision References
Part No.
ADR445
ADR02
ADR435
ADR395
AD586
SET
, the full-scale error is 0.025% FSR + 0.075% FSR = 0.1% FSR.
Initial Accuracy
(mV Maximum)
±2
±3
±2
±5
±2.5
SET
SET
, the offset error is 0.075% FSR. This value
. For example, with the measured channel at
SET
are enabled and by the dc crosstalk from
SET
resistor in current output mode,
SET
specifications in Table 1 are
Long-Term Drift
(ppm Typical)
50
50
40
50
15
SET
SET
selected and
, the offset error
SET
is propor-
SET
Temperature Drift (ppm/°C Maximum)
3
3
3
9
10
Rev. B | Page 40 of 44
There are four possible sources of error to consider when choosing
a voltage reference for high accuracy applications: initial
accuracy, temperature coefficient of the output voltage, long-
term drift, and output voltage noise.
Initial accuracy error on the output voltage of an external refer-
ence can lead to a full-scale error in the DAC. Therefore, to
minimize these errors, a reference with low initial accuracy
error specification is preferred. Choosing a reference with an
output trim adjustment, such as the ADR425, allows a system
designer to trim system errors out by setting the reference
voltage to a voltage other than the nominal. The trim adjust-
ment can be used at any temperature to trim out any error.
Long-term drift is a measure of how much the reference output
voltage drifts over time. A reference with a tight long-term drift
specification ensures that the overall solution remains relatively
stable over its entire lifetime.
The temperature coefficient of a reference’s output voltage affects
INL, DNL, and TUE. A reference with a tight temperature
coefficient specification should be chosen to reduce the depend-
ence of the DAC output voltage to ambient temperature.
In high accuracy applications, which have a relatively low noise
budget, reference output voltage noise must be considered.
Choosing a reference with as low an output noise voltage as practi-
cal for the system resolution required is important. Precision
voltage references such as the
low output noise in the 0.1 Hz to 10 Hz region. However, as the
circuit bandwidth increases, filtering the output of the reference
may be required to minimize the output noise.
DRIVING INDUCTIVE LOADS
When driving inductive or poorly defined loads, a capacitor
may be required between I
0.01 μF capacitor between I
a load of 50 mH. The capacitive component of the load may
cause slower settling, although this may be masked by the set-
tling time of the AD5757. There is no maximum capacitance
limit for the current output of the AD5757.
OUT_x
OUT_x
ADR435
and AGND to ensure stability. A
and AGND ensures stability of
0.1 Hz to 10 Hz Noise
(μV p-p Typical)
2.25
10
8
8
4
(XFET design) produce
Data Sheet