AD5555CRU Analog Devices Inc, AD5555CRU Datasheet - Page 13

• 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

PROGRAMMABLE CURRENT SOURCE
Figure 23 shows a versatile V-to-I conversion circuit using
improved Howland Current Pump. In addition to the precision
current conversion it provides, this circuit enables a bidirec-
tional current flow and high voltage compliance. This circuit
can be used in a 4 mA to 20 mA current transmitter with up to
a 500 Ω of load. In Figure 23, it shows that if the resistor
network is matched, the load current is
R3, in theory, can be made small to achieve the current needed
within the U3 output current driving capability. This circuit is
versatile such that the AD8510 can deliver ±20 mA in both
directions, and the voltage compliance approaches 15 V, which
is mainly limited by the supply voltages of U3. However, users
must pay attention to the compensation. Without C1, it can be
shown that the output impedance becomes
I
Z
L
O
=
=
(
R1
R2
(
R1
R3
R
+
2
R3
R
+ ′
1
)
′
R
R3
×
3
V
′
(
)
REF
R1
–
R
+
×
1
′
D
R2
(
R2
)
+
R3
)
Rev. C | Page 13 of 20
(5)
(6)
If the resistors are perfectly matched, Z
desirable, and the resistors behave as an ideal current source.
On the other hand, if they are not matched, Z
positive or negative. The latter can cause oscillation. As a result,
C1 is needed to prevent the oscillation. For critical applications,
C1 could be found empirically but typically falls in the range of
a few picofarads.
V
REF
AD5545/AD5555
Figure 23. Programmable Current Source with Bidirectional
Current Control and High Voltage Compliance Capabilities
U1
V
V
GND
V
REF
DD
DD
R
FB
I
OUT
U2
AD8628
150kΩ
AD5545/AD5555
O
150kΩ
R1
R1'
is infinite, which is
15kΩ
O
R2'
can be either
AD8510
10pF
V
V
15kΩ
V+
V–
C1
R2
DD
SS
U3
02918- 0- 023
LOAD
R3'
50Ω
R3
50Ω
V
L
I
L