AD5735 Analog Devices, AD5735 Datasheet - Page 45

• Manufacturer Part Number: AD5735
• Description: Quad Channel, 12-Bit, Serial Input, 4-20 mA & Voltage Output DAC with Dynamic Power Control
• Manufacturer: Analog Devices

Specifications of AD5735

• Resolution (bits): 12bit
• Dac Settling Time: 11µs
• Max Pos Supply (v): +33V
• Single-supply: No
• Dac Type: I or V Out
• Dac Input Format: SPI

APPLICATIONS INFORMATION
VOLTAGE AND CURRENT OUTPUT PINS ON THE
SAME TERMINAL
When using a channel of the AD5735, the current and voltage
output pins can be connected to two separate terminals or tied
together and connected to a single terminal. The two output
pins can be tied together because only the voltage output or the
current output can be enabled at any one time. When the current
output is enabled, the voltage output is in tristate mode, and when
the voltage output is enabled, the current output is in tristate mode.
When the two output pins are tied together, the POC pin must
be tied low and the POC bit in the main control register set to 0,
or, if the POC pin is tied high, the POC bit in the main control
register must be set to 1 before the current output is enabled.
As shown in the Absolute Maximum Ratings section, the output
tolerances are the same for both the voltage and current output
pins. The +V
that current leakage into these pins is negligible when the part
is operated in current output mode.
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 four 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
proportionally as more current channels are enabled; the offset
error is 0.056% FSR on each of two channels, 0.029% FSR on
each of three channels, and 0.01% FSR 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
and another channel going from zero to full scale, the dc crosstalk
is −0.011% FSR. With two other channels going from zero to full
scale, the dc crosstalk 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,
Table 37. Recommended Precision Voltage References
Part No.
ADR445
ADR02
ADR435
ADR395
AD586
Data Sheet
SET
SET
, the offset error is 0.075% FSR. This value decreases
. For example, with the measured channel at 0x8000
SENSE_x
and −V
Initial Accuracy
(mV Maximum)
±2
±3
±2
±5
±2.5
SET
are enabled and by the dc crosstalk from
SET
SENSE_x
resistor in current output mode,
SET
connections are buffered so
specifications in Table 1 are
SET
SET
, the offset error
Long-Term Drift
(ppm Typical)
50
50
40
50
15
SET
selected and
is propor-
SET
Rev. A | Page 45 of 48
with the measured channel at 0xFFFF and three channels at zero
scale, the full-scale error is 0.025% FSR. Similarly, if only one
channel is enabled in current output mode with the internal R
the full-scale error is 0.025% FSR + 0.075% FSR = 0.1% FSR.
PRECISION VOLTAGE REFERENCE SELECTION
To achieve the optimum performance from the
full operating temperature range, a precision voltage reference
must be used. Care should be taken with the selection of the
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 AD5735.
Four possible sources of error must be considered when choosing
a voltage reference for high accuracy applications: initial accuracy,
long-term drift, temperature coefficient of the output voltage,
and output voltage noise.
Initial accuracy error on the output voltage of an external ref-
erence can lead to a full-scale error in the DAC. Therefore, to
minimize these errors, a reference with a low initial accuracy
error specification is preferred. Choosing a reference with an
output trim adjustment, such as the ADR435, allows a system
designer to trim out system errors 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 the reference output voltage affects
INL, DNL, and TUE. A reference with a tight temperature coef-
ficient specification should be chosen to reduce the dependence
of the DAC output voltage on ambient temperature.
In high accuracy applications, which have a relatively low noise
budget, reference output voltage noise must be considered. Choos-
ing a reference with as low an output noise voltage as practical
for the system resolution required is important. Precision voltage
references such as the
noise in the 0.1 Hz to 10 Hz bandwidth. However, as the circuit
bandwidth increases, filtering the output of the reference may
be required to minimize the output noise.
Temperature Coefficient
(ppm/°C Maximum)
3
3
3
9
10
ADR435
(XFET® design) produce low output
0.1 Hz to 10 Hz Noise
(μV p-p Typical)
2.25
10
8
8
4
AD5735
AD5735
over its
SET
,