Datasheet
Data Sheet AD5755-1
Rev. E | Page 45 of 52
Reducing AI
CC
Current Requirements
There are two main methods that can be used to reduce the
AI
CC
current requirements. One method is to add an external
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
DCDC_x
pin
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
CC
transient current requirements. Figure 83 shows a plot of AI
CC
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.
0
4
12
8
16
24
20
28
32
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
AI
CC
CURRENT (A)
0mA TO 24mA RANGE
1kΩ LOAD
f
SW
= 410kHz
INDUCTOR = 10µH (XAL4040-103)
T
A
= 25°C
09226-185
0 0.5 1.0 1.5 2.0 2.5
I
OUT_x
CURRENT (mA)/V
BOOST_x
VOLTAGE (V)
TIME (ms)
AI
CC
I
OUT
V
BOOST
Figure 83. AI
CC
Current vs. Time for 24 mA Step Through 1 kΩ Load
with External 51 kΩ Compensation Resistor
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
AI
CC
CURRENT (A)
0mA TO 24mA RANGE
500Ω LOAD
f
SW
= 410kHz
INDUCTOR = 10µH (XAL4040-103)
T
A
= 25°C
09226-186
0
4
12
8
16
24
20
28
32
0 0.5 1.0 1.5 2.0 2.5
I
OUT_x
CURRENT (mA)/V
BOOST_x
VOLTAGE (V)
TIME (ms)
AI
CC
I
OUT
V
BOOST
Figure 84. AI
CC
Current vs. Time for 24 mA Step Through 500 Ω Load
with External 51 kΩ Compensation Resistor
Using slew rate control can greatly reduce the AV
CC
supplies
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
BOOST
corresponds to the dc-to-dc converter’s output
voltage).
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
AI
CC
CURRENT (A)
0mA TO 24mA RANGE
1kΩ LOAD
f
SW
= 410kHz
INDUCTOR = 10µH (XAL4040-103)
T
A
= 25°C
0
4
12
8
16
24
20
28
32
09226-187
0 1 2 3 4 5 6
I
OUT_x
CURRENT (mA)/V
BOOST_x
VOLTAGE (V)
TIME (ms)
AI
CC
I
OUT
V
BOOST
Figure 85. AI
CC
Current vs. Time for 24 mA Step Through 1 kΩ Load
with Slew Rate Control