AD5452 Analog Devices, AD5452 Datasheet - Page 19

• Manufacturer Part Number: AD5452
• Description: 12-Bit High Bandwidth Multiplying DACs with Serial Interface
• Manufacturer: Analog Devices

Specifications of AD5452

• Resolution (bits): 12bit
• Dac Update Rate: 2.7MSPS
• Dac Settling Time: 160ns
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Ser,SPI

D
C
ma
the feedback element of an op amp and R
resistor as shown in Figure 49, the output voltage is inversely
proportional to the digital input fraction, D.
For D = 1 − 2
As D is reduced, the output voltage increases. For small values
of the digital fraction, D, it is important to ensure that the
amplifier does not saturate and that the required accuracy is
met. For example, an 8-bit DAC driven with the binary code
0x10 (00010000), that is, 16 decimal, in the circuit of Figur
should cause the output voltage to be 16 times V
However, if the DAC has a linearity specification o ±0.5 LSB, D
can have w
Therefore, the poss
to 16.5 V
maximum error of 0.2%.
DAC leakage current is also a potential error source in divider
circuits. The leakage current must be counterbalanced by an
opposite current supplied f
Because only a fraction, D, of the current in the V
routed to the I
where R is the DAC resistance at the V
For
(that is, 1/D) of 16, the error voltage is 1.6 mV.
urrent-steering DACs are very flexible and lend themselves to
IVIDER OR PROGRAMMABLE GAIN ELEMENT
ny different applications. If this type of DAC is connected as
a DAC leakage current of 10 nA, R = 10 kΩ, and a gain
Output Error Voltage Dueto Leakage = (Leakage × R)/D
V
OUT
IN
Figure 49. Current-Steering DAC Used as a Divider or
—an error of 3%, even though the DAC itself has a
eight anywhere in the range of 15.5/256 to 16
=
−
−n
NOTE
ADDITIONAL PINS OMITTED FOR CLARITY
OUT
V
D
, the output voltage is
IN
1 terminal, the output voltage changes as follows
V
ible output voltage is in the r
=
IN
Programmable Gain Element
I
OUT
(
1
−
− 2
1
V
R
FB
IN
−
rom the op amp through the DAC.
n
GND
)
V
V
DD
DD
V
REF
REF
FB
terminal.
is used as the inp
V
OUT
ange of 15.5 V
IN
REF
.
f
terminal is
.5/256.
e 49
Rev. E | Page 19 of 32
ut
IN
:
R
When selecting a reference for
output DACs, pay attention to the reference’s output voltage
temperature coefficient specification. This parameter not only
affects the full-scale error, but also may affect the linearity (INL
and DNL) performance. The reference temperature coefficient
should be consistent with the system accuracy specifications.
For example, an 8-bit system is required to hold its overall
specification to within 1 LSB over the temperature range 0°C t
50°C, and the system’s maximum temperature drift should be
less than 78 ppm/°C.
A 12-bit system within
drift of 10 ppm/°C. Choosing a precision reference with a low
output temperature coefficient minimizes this error source.
Table 7 lists some dc references available from Analog Devices
that are suitable for use with this range of current-output DACs
AMPLIFIER SELECTION
The primary requirement for t
amplifier with low input bias currents and low input offset voltag
The input offset voltage of an op amp is multiplied by the variable
gain of the circuit due to the code-dependent output resistance of
the DAC. A change in this noise gain between two adjacent digital
fractions produces a step change in the output voltage due to the
offset voltage of the amplifier’s input. This output voltage change
is superimposed on the desired change in output between the two
codes and gives rise to a differential linearity error, which if
large enough, could cause the DAC to be nonmonotonic.
The input bias current of an op amp generates an offset at t
voltage output as a result of the bias current flowing in the
feedback resistor, R
low enough to prevent significant errors in 12-bit applications
However, for 14-bit applications, some consideration should be
given to selecting an appropriate amplifier.
Common-mode rejection of the op amp is im
switching circuits because it produces a code-dependent error
at the voltage output of the circuit. Most op amps have adequate
common-mode rejection for use at 8-, 10-, and 12-bit resolutions.
Provided that the DAC switches are driven from true wideband
low impedance sources (V
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, i
is important to minimize capacitance at the V
output node in this application) of the DAC. This is done by using
low input-capacitance buffer amplifiers and careful board design.
Most single-supply circuits include ground as part of the analog
signal range, which in turn requires an amplifier that can handle
rail-to-rail signals. There is a large range of single-supply amplifiers
available from Analog Devices.
EFERENCE SELECTION
AD5450/AD5451/AD5452/AD5453
FB
. Most op amps have input bias currents
2 LSB accuracy requires a maximum
IN
and AGND), they settle quickly.
he current-steering mode is an
use with this series of current-
REF
portant in voltage-
node (the voltage
he
.
t
o
e.
.