AD5555CRU Analog Devices Inc, AD5555CRU Datasheet - Page 12

• Manufacturer Part Number: AD5555CRU
• Description: IC DAC 14BIT DUAL SRL IN 16TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD5555CRU

• Rohs Status: RoHS non-compliant
• Settling Time: 500ns
• Number Of Bits: 14
• Data Interface: Serial
• Number Of Converters: 2
• Voltage Supply Source: Single Supply
• Power Dissipation (max): 55µW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP

AD5545/AD5555
APPLICATIONS INFORMATION
STABILITY
In the I-to-V configuration, the I
inverting node of the op amp must be connected as close as
possible, and proper PCB layout techniques must be employed.
Because every code change corresponds to a step function, gain
peaking may occur if the op amp has limited GBP, and if there
is excessive parasitic capacitance at the inverting node.
An optional compensation capacitor, C1, can be added for
stability as shown in Figure 20. C1 should be found empirically,
but 6 pF is generally more than adequate for the compensation.
POSITIVE VOLTAGE OUTPUT
To achieve the positive voltage output, an applied negative
reference to the input of the DAC is preferred over the output
inversion through an inverting amplifier because of the
resistors’ tolerance errors. To generate a negative reference, the
reference can be level shifted by an op amp such that the V
and GND pins of the reference become the virtual ground and
−2.5 V, respectively (see Figure 21).
Figure 20. Operational Compensation Capacitor for Gain Peaking
V
REF
U4
1/2
AD8620
V+
V–
Figure 21. Positive Voltage Output Configuration
+5V
–5V
U1
V
REF
GND
V
V
V
ADR03
DD
DD
AD5545/AD5555
OUT
–2.5V
GND
V
U3
AD5545/AD5555
IN
R
FB
U1
Prevention
V
+5V
GND
V
REF
DD
I
OUT
OUT
R
C1
FB
of the DAC and the
I
OUT
U2
C1
AD8628
U2
AD8628
1/2
0 < V
02918- 0- 020
O
02918- 0- 021
< +2.5
V
O
V
OUT
O
Rev. C | Page 12 of 20
BIPOLAR OUTPUT
The AD5545/AD5555 is inherently a 2-quadrant multiplying
DAC. It can easily be set up for unipolar output operation. The
full-scale output polarity is the inverse of the reference input
voltage.
In some applications, it may be necessary to generate the full
4-quadrant multiplying capability or a bipolar output swing. This
is easily accomplished by using an additional external amplifier,
U4, configured as a summing amplifier (see Figure 22). In this
circuit, the second amplifier, U4, provides a gain of 2, which
increases the output span magnitude to 5 V. Biasing the external
amplifier with a 2.5 V offset from the reference voltage results in a
full 4-quadrant multiplying circuit. The transfer equation of this
circuit shows that both negative and positive output voltages are
created because the input data (D) is incremented from code zero
(V
+2.5 V).
For the AD5545, the external resistance tolerance becomes the
dominant error that users should be aware of.
5V
OUT
ADR03
V
V
V
OUT
GND
= −2.5 V) to midscale (V
OUT
OUT
V
Figure 22. Four-Quadrant Multiplying Application Circuit
IN
U3
= (D/32,768 − 1) × V
= (D/8192 − 1) × V
AD5545/AD5555
U1
+5V
V
V
GND
DD
REF
R
FB
I
OUT
C1
REF
U2
OUT
REF
AD8620
(AD5555)
1/2
= 0 V) to full scale (V
(AD5545)
10kΩ±0.01% 10kΩ±0.01%
5kΩ±0.01%
R3
R1
–2.5 < V
U4
R2
1/2
AD8620
C2
V+
V–
O
< +2.5
OUT
+5V
–5V
02918- 0- 022
=
V
(3)
(4)
O