XDL604 datasheet(14/28 Pages) TOREX

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XDL603/XDL604 Series

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OPERATIONAL EXPLANATION (Continued)

< CE Function >

When an “H” voltage (VEN/SSH) is input to the EN/SS pin, normal operation is performed after the output voltage is started up by

the soft start function, normal operation is performed. When the “L” voltage (VEN/SSL) is input to the EN/SS pin, the circuit enters

the standby state, the supply current is suppressed to the standby current ISTB (TYP. 1.65μA), and the High side driver FET and

Low side driver FET are turned off.

< Soft Start Function >

This function gradually starts up the output voltage to suppress the inrush current.

The soft start time is the time until the output voltage from VEN/SSH reaches 90% of the output voltage set value, and when the

output voltage increases further, the soft start function is cancelled to switch to normal operation.

Internal Soft Start Time

The internal soft start time (tSS1) is configured so that after the “H” voltage (VEN/SSH) is input to the EN/SS pin, the standard voltage

connected to the error amplifier increases linearly during the soft-start period. This causes the output voltage to increase

proportionally to the standard voltage increase. This operation suppresses the inrush current and smoothly increases the output

voltage.

< Internal soft start EN/SS circuit >

< Overview of internal soft start >

External Setting Soft Start Time

The external setting soft start time (tSS2) can adjust the increase speed of the standard voltage in the IC by adjusting the EN/SS

pin voltage inclination during startup using externally connected component RSS and CSS. This makes it possible to externally

adjust the soft start time.

Soft start time (tSS2) is approximated by the equation below according to values of V1, RSS, and CSS

When tss2 is shorter than tss1, the output voltage rises at the internal soft start time.

tss2=Css×Rss× ln ( V1 / (V1-1.45V) )

【

Setting Example】

CSS = 0.47μF, RSS = 430kΩ, V1 = 12V

tSS2 = 0.47μF x 430kΩ x ( ln (12V/(12V-1.45V)) = 26ms

< External soft start EN/SS circuit >

< Overview of external soft start >

EN/SS

VOUT

tss1

90% of setting voltage

RSS

CSS

EN/SS

VOUT

tss2

90% of setting voltage

1.45V

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