Datasheet
AD5735 Data Sheet
Rev. C | Page 44 of 48
Reducing AI
CC
Current Requirements
Two main methods 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. These methods
can be used together.
Adding an External Compensation Resistor
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 reduces the AI
CC
transient current requirements. Figure 80 shows a plot of AI
CC
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
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 24m
A
RANGE
1kΩ LOAD
f
SW
= 410kHz
INDUCTOR = 10µH (XAL4040-103)
T
A
= 25°C
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
09961-185
Figure 80. 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
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
VO
LTAGE (V)
TIME (ms)
AI
CC
I
OUT
V
BOOST
09961-186
Figure 81. AI
CC
Current vs. Time for 24 mA Step Through 500 Ω Load
with External 51 kΩ Compensation Resistor
Using Slew Rate Control
Using slew rate control can greatly reduce the current require-
ments of the AV
CC
supply, as shown in Figure 82.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
AI
CC
CURRENT (A)
0mA
T
O 24mA
RANGE
1kΩ LOAD
f
SW
= 410kHz
INDUCTOR = 10µH (XAL4040-103)
T
A
= 25°C
0
4
12
8
16
24
20
28
32
0 1
2
3
4 5
6
I
OUT_x
CURRENT (mA
)/
V
BOOST_x
VO
LTAGE (V)
TIME (ms)
AI
CC
I
OUT
V
BOOST
09961-187
Figure 82. AI
CC
Current vs. Time for 24 mA Step Through 1 kΩ Load
with Slew Rate Control
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
BOOST
corresponds to the output voltage of the
dc-to-dc converter.)