XCL225 datasheet(9/27 Pages) TOREX

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XCL225/XCL226

Series

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TYPICAL APPLICATION CIRCUIT(Continued)

The output voltage can be set by adding an external dividing resistor.

The output voltage is determined by the equation below based on the values of RFB1 and RFB2.

VOUT=VFB× (RFB1+RFB2)/RFB2

With RFB1+RFB2≦1MΩ

Adjust the value of the phase compensation speed-up capacitor CFB using the equation below.

A target value for fzfb of optimum is below.

【

Setting Example】

When CL is 10μF, fzfb=24kHz

When CL is 20μF, fzfb=17kHz

【

Setting Example】

To set output voltage to 5V with fosc=1.2MHz, CL=20μF, L=4.3μH

When RFB1=680kΩ, RFB2=120kΩ, VOUT=0.75V× (680kΩ+120kΩ) / 120kΩ=5.0V

And fzfb is set to a target of 17kHz using the above equation,

CFB=1/(2×π×17kHz×680kΩ)=13.8pF

* The setting range for the output voltage is 1.0V to 15.0V.

The condition VOUT/VIN ≧ 0.14 must be satisfied.

<Soft-start Time Setting>

The soft-start time can be adjusted by adding a capacitor and a resistor to the EN/SS pin.

Soft-start time (tss2) is approximated by the equation below according to values of VEN/SS, RSS, and CSS.

tss2=Css×Rss× (-ln ((VEN/SS-1.45)/VEN/SS)) )

【

Setting Example】

When CSS=0.47μF, RSS=430kΩ and VEN/SS=12V, tSS2=0.47x10-6 x 430 x 103 x (-ln ((12-1.45)/12)) =26ms (Approx.)

*The soft-start time is the time from the start of VEN/SS until the output voltage reaches 90% of the set voltage.

If the EN/SS pin voltage rises steeply without connecting CSS and RSS (RSS=0Ω), Output rises with taking

the soft-start time of tss1=1.0ms (TYP.) which is fixed internally.

fzfb







VEN/SS

VOUT

90 % of se tting voltage

tSS1

tSS2

EN/SS

CSS

RSS

VEN/SS

fzfb

L 





XCL225 Datasheet(PDF) 9 Page - Torex Semiconductor

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