Data Sheet

ADPL44002

analog.com

Rev. 0

16 of 23

Soft Start

The ADPL44002 uses an internal soft start (when the SS pin is left open) to limit the inrush current when the output

is enabled. The start-up time for the 3.3V option is approximately 400μs from the time the EN active threshold is

crossed to when the output reaches 90% of its final value. As shown in Figure 30, the start-up time is independent of

the output voltage setting.

Figure 30. Typical Start-Up Behavior

An external capacitor connected to the SS pin determines the soft start time. The SS pin can be left open for a typical

400μs start-up time. Do not ground this pin. When an external soft start capacitor (CSS) is used, the soft start time is

determined by the following equation:

SSTIME (sec) = tSTARTUP (OPEN) + 6 × CSS /ISS

(6)

where: tSTARTUP (OPEN) is the start-up time at CSS = (OPEN) (typically 400µs).

CSS is the soft start capacitor (F).

ISS is the soft start current (typically 1.15µA).

Figure 31. Typical Soft Start Behavior, Different CSS

TIME (ms)

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0

1

2

3

4

6

5

VEN

VOUT = 1.8V

VOUT = 3.3V

VOUT = 5.0V

TIME (ms)

10

9

8

7

6

5

4

3

2

1

0

0

0.5

1.0

2.0

3.0

3.5

1.5

2.5

VEN

NO SS CAP

1nF

2nF

4.7nF

6.8nF

10nF