Datasheet
AD5737 Data Sheet
Rev. C | Page 38 of 44
AI
CC
SUPPLY REQUIREMENTS—SLEWING
The AI
CC
current requirement while slewing is greater than in
static operation because the output power increases to charge
the output capacitance of the dc-to-dc converter. This transient
current can be quite large (see Figure 57), although the methods
described in the Reducing AI
CC
Current Requirements section
can reduce the requirements on the AV
CC
supply.
If not enough AI
CC
current can be provided, the AV
CC
voltage
drops. Due to this AV
CC
drop, the AI
CC
current required for
slewing increases further, causing the voltage at AV
CC
to drop
further (see Equation 3). In this case, the V
BOOST_x
voltage and,
therefore, the output voltage, may never reach their intended
values. Because the AV
CC
voltage is common to all channels,
this voltage drop may also affect other channels.
0
5
10
15
20
25
30
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.5 1.0 1.5 2.0 2.5
I
OUT_x
CURRENT (mA)/V
BOOST_x
VOLTAGE (V)
AI
CC
CURRENT (A)
TIME (ms)
AI
CC
I
OUT
V
BOOST
0mA TO 24mA RANGE
1kΩ LOAD
f
SW
= 410kHz
INDUCTOR = 10µH (XAL4040-103)
T
A
= 25°C
10067-184
Figure 57. AI
CC
Current vs. Time for 24 mA Step Through 1 kΩ Load
with Internal Compensation Resistor
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 58 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 59.
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
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
10067-185
Figure 58. 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
VOLTAGE (V)
TIME (ms)
AI
CC
I
OUT
V
BOOST
10067-186
Figure 59. AI
CC
Current vs. Time for 24 mA Step Through 500 Ω Load
with External 51 kΩ Compensation Resistor