ADR02 datasheet(44/48 Pages) AD

44 / 48 page

AD5735

Data Sheet

Rev. B | Page 44 of 48

Reducing AICC Current Requirements

Two main methods can be used to reduce the AICC 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 COMPDCDC_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 AICC

transient current requirements. Figure 80 shows a plot of AICC

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.

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0mA TO 24mA RANGE

1kΩ LOAD

fSW = 410kHz

INDUCTOR = 10µH (XAL4040-103)

TA = 25°C

0.5

1.0

1.5

2.0

2.5

TIME (ms)

AICC

IOUT

VBOOST

Figure 80. AICC Current vs. Time for 24 mA Step Through 1 kΩ Load

with External 51 kΩ Compensation Resistor

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0mA TO 24mA RANGE

500Ω LOAD

fSW = 410kHz

INDUCTOR = 10µH (XAL4040-103)

TA = 25°C

0.5

1.0

1.5

2.0

2.5

TIME (ms)

AICC

IOUT

VBOOST

Figure 81. AICC 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 AVCC supply, as shown in Figure 82.

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0mA TO 24mA RANGE

1kΩ LOAD

fSW = 410kHz

INDUCTOR = 10µH (XAL4040-103)

TA = 25°C

TIME (ms)

AICC

IOUT

VBOOST

Figure 82. AICC 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. (VBOOST corresponds to the output voltage of the

dc-to-dc converter.)

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