AD5735 Analog Devices, AD5735 Datasheet - Page 44

• Manufacturer Part Number: AD5735
• Description: Quad Channel, 12-Bit, Serial Input, 4-20 mA & Voltage Output DAC with Dynamic Power Control
• Manufacturer: Analog Devices

Specifications of AD5735

• Resolution (bits): 12bit
• Dac Settling Time: 11µs
• Max Pos Supply (v): +33V
• Single-supply: No
• Dac Type: I or V Out
• Dac Input Format: SPI

AD5735
Reducing AI
Two main methods can be used to reduce the AI
requirements. One method is to add an external compensation
resistor, and the other is to use slew rate control. These methods
can be used together.
Adding an External Compensation Resistor
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 reduces the AI
transient current requirements. Figure 80 shows a plot of AI
current for a 24 mA step through a 1 kΩ load when using a 51 kΩ
compensation resistor. The compensation resistor reduces the
current requirements through smaller loads even further, as
shown in Figure 81.
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 81. AI
Figure 80. AI
0
0
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
with External 51 kΩ Compensation Resistor
AI
I
V
CC
OUT
CC
0.5
0.5
BOOST
Current Requirements
CC
Current vs. Time for 24 mA Step Through 500 Ω Load
Current vs. Time for 24 mA Step Through 1 kΩ Load
1.0
1.0
TIME (ms)
TIME (ms)
AI
I
V
INDUCTOR = 10µH (XAL4040-103)
OUT
BOOST
CC
1.5
1.5
0mA TO 24mA RANGE
f
SW
2.0
2.0
500Ω LOAD
T
= 410kHz
A
= 25°C
CC
current
DCDC_x
2.5
2.5
32
28
24
20
16
12
8
4
0
32
28
24
20
16
12
8
4
0
pin
CC
Rev. A | Page 44 of 48
CC
Using Slew Rate Control
Using slew rate control can greatly reduce the current require-
ments of the AV
When using slew rate control, it is important to remember that
the output cannot slew faster than the dc-to-dc converter. The
dc-to-dc converter slews slowest at higher currents through large
loads (for example, 1 kΩ). The 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 80 and
Figure 81. (V
dc-to-dc converter.)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Figure 82. AI
0
0
0mA TO 24mA RANGE
1kΩ LOAD
f
INDUCTOR = 10µH (XAL4040-103)
T
SW
A
AI
I
V
= 25°C
OUT
BOOST
BOOST
= 410kHz
1
CC
CC
CC
Current vs. Time for 24 mA Step Through 1 kΩ Load
corresponds to the output voltage of the
supply, as shown in Figure 82.
2
with Slew Rate Control
TIME (ms)
3
4
5
Data Sheet
6
32
28
24
20
16
12
8
4
0