AD5755-1 Analog Devices, AD5755-1 Datasheet - Page 45

• Manufacturer Part Number: AD5755-1
• Description: Quad Channel, 16-Bit, Serial Input, 4-20mA & Voltage Output DAC, Dynamic Power Control, HART Connectivity
• Manufacturer: Analog Devices

Specifications of AD5755-1

• Resolution (bits): 16bit
• Dac Update Rate: 91kSPS
• Dac Settling Time: 11µs
• Max Pos Supply (v): +33V
• Single-supply: No
• Dac Type: I or V Out
• Dac Input Format: SPI

Data Sheet
Reducing AI
There are two main methods that can be used to reduce the
AI
compensation resistor, and the other is to use slew rate control.
Both of these methods can be used in conjunction.
A compensation resistor can be placed at the COMP
in series with the 10 nF compensation capacitor. A 51 kΩ exter-
nal compensation resistor is recommended. This compensation
increases the slew time of the current output but eases the AI
transient current requirements. Figure 83 shows a plot of AI
current for a 24 mA step through a 1 kΩ load when using a
51 kΩ compensation resistor. This method eases the current
requirements through smaller loads even further, as shown in
Figure 84.
CC
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Figure 83. AI
current requirements. One method is to add an external
0
0
0mA TO 24mA RANGE
1kΩ LOAD
f
INDUCTOR = 10µH (XAL4040-103)
T
SW
A
= 25°C
= 410kHz
CC
with External 51 kΩ Compensation Resistor
CC
Current Requirements
0.5
Current vs. Time for 24 mA Step Through 1 kΩ Load
1.0
TIME (ms)
AI
I
V
OUT
BOOST
CC
1.5
2.0
DCDC_x
2.5
32
28
24
20
16
12
8
4
0
pin
CC
Rev. B | Page 45 of 52
CC
Using slew rate control can greatly reduce the AV
current requirements, as shown in Figure 85. When using slew
rate control, attention should be paid to the fact that the output
cannot slew faster than the dc-to-dc converter. The dc-to-dc
converter slews slowest at higher currents through large (for
example, 1 kΩ) loads. This slew rate is also dependent on the
configuration of the dc-to-dc converter. Two examples of the
dc-to-dc converter output slew are shown in Figure 83 and
Figure 84 (V
voltage).
Figure 84. AI
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Figure 85. AI
0
0
0
0
0mA TO 24mA RANGE
1kΩ LOAD
f
INDUCTOR = 10µH (XAL4040-103)
T
SW
A
BOOST
AI
I
V
= 25°C
OUT
with External 51 kΩ Compensation Resistor
BOOST
CC
= 410kHz
1
AI
I
V
CC
CC
OUT
0.5
BOOST
Current vs. Time for 24 mA Step Through 500 Ω Load
CC
Current vs. Time for 24 mA Step Through 1 kΩ Load
corresponds to the dc-to-dc converter’s output
with Slew Rate Control
2
1.0
TIME (ms)
TIME (ms)
INDUCTOR = 10µH (XAL4040-103)
3
1.5
0mA TO 24mA RANGE
4
f
SW
2.0
500Ω LOAD
T
= 410kHz
5
A
= 25°C
AD5755-1
CC
supplies
2.5
6
32
28
24
20
16
12
8
4
0
32
28
24
20
16
12
8
4
0