AD5544 Analog Devices, AD5544 Datasheet - Page 13

• Manufacturer Part Number: AD5544
• Description: Quad, Current-Output, Serial-Input 16-/14-Bit DACs
• Manufacturer: Analog Devices

Specifications of AD5544

• Resolution (bits): 16bit
• Dac Update Rate: 500kSPS
• Dac Settling Time: 0.9µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Ser,SPI

Data Sheet
THEORY OF OPERATION
The
current output DACs, respectively. Each DAC has its own inde-
pendent multiplying reference input. Both the
AD5554
a configurable asynchronous RS pin for half-scale (MSB = 1) or
zero-scale (MSB = 0) preset. In addition, an LDAC strobe enables
4-channel, simultaneous updates for hardware synchronized
output voltage changes.
DIGITAL-TO-ANALOG CONVERTER (DAC)
Each part contains four current-steering R-R ladder DACs.
Figure 20. shows a typical equivalent DAC. Each DAC contains
a matching feedback resistor for use with an external I-to-V
converter amplifier. The R
external amplifier. The I
input of the external amplifier. The A
connected to the load point, requiring full 16-bit accuracy. These
DACs are designed to operate with both negative and positive
reference voltage.
The V
switches on and off. Note that a matching switch is used in series
with the internal 5 kΩ feedback resistor. If users attempt to
measure the value of R
continuity. An additional V
during high temperature applications, minimizing zero-scale
leakage currents that double every 10°C. The DAC output
voltage is determined by V
following equations:
Note that the output polarity is opposite the V
reference voltages.
V
DIGITAL INTERFACE CONNECTIONS OMITTED FOR CLARITY.
SWITCHES S1 AND S2 ARE CLOSED, AND V
REF
X
AD5544
V
V
DD
OUT
OUT
V
SS
2R
use a 3-wire, SPI-compatible serial data interface, with
power pin is used only by the logic to drive the DAC
=
=
−
−
and the
DGND
Figure 20. Typical Equivalent DAC Channel
V
V
R
REF
REF
2R
×
×
FROM OTHER DACS A
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FB
16
65
, power must be applied to V
OUT
,
D
,
D
384
FB
536
SS
REF
x terminal connects to the inverting
x pin connects to the output of the
R
bias pin is used to guard the substrate
and the digital data (D) in the
2R
contain four 16-bit and 14-bit,
(
(
for
for
DD
GND
the
R
the
MUST BE POWERED.
GND
x pin should be Kelvin-
AD
AD
R
S2
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5544
5kΩ
REF
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polarity for dc
S1
)
DD
)
to achieve
and the
V
R
A
A
I
OUT
DD
FB
GND
GND
X
X
F
X
Rev. F | Page 13 of 28
(1)
(2)
These DACs are also designed to accommodate ac reference input
signals. Both the
reference voltages in the range of −15 V to +15 V. The reference
voltage inputs exhibit a constant nominal input resistance of 5 kΩ ±
30%. On the other hand, the I
DAC outputs are code dependent and produce various output
resistances and capacitances. The choice of external amplifier
should take into account the variation in impedance generated by
the
The feedback resistance, in parallel with the DAC ladder resistance,
dominates output voltage noise. For multiplying mode applications,
an external feedback compensation capacitor, C
to provide a critically damped output response for step changes in
reference input voltages. Figure 21 shows the gain vs. frequency
performance at various attenuation settings using a 23 pF external
feedback capacitor connected across the I
for the
analog performance, power supply bypassing of 0.01 µF, in parallel
with 1 µF, is recommended. Under these conditions, a clean power
supply with low ripple voltage capability should be used. Switching
power supplies is usually not suitable for this application due to
the higher ripple voltage and PSS frequency-dependent charac-
teristics. It is best to derive the supply of the
from system analog supply voltages. Do not use the digital
supply (see Figure 22).
AD5544/AD5554
Figure 21.
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–2
–4
–6
–8
100k
2
0
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and the AD5554, respectively. To maintain good
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on the inverting input node of the amplifier.
Reference Multiplying Bandwidth vs. Code
1M
and the
FREQUENCY (Hz)
OUT
A, I
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OUT
AD5544/AD5554
B, I
10M
OUT
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OUT
accommodate input
x and R
C, and I
FB
, may be needed
FB
x terminals
OUT
100M
D