Data Sheet

ADPL42002

analog.com

Rev. 1

16 of 22

Soft Start

The ADPL42002 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 the final value. As shown in Figure 30, the start-up time is indepezndent

of the output voltage setting.

Figure 30. Typical Start-Up Behavior

An external capacitor connected to the SS pin determines the soft-start time. This 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) = tSTART-UPat0pF + (0.6 × CSS)/ISS

(7)

Where:

tSTART-UP at 0 pF is the start-up time at CSS = 0pF (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