LM2672 datasheet(13/25 Pages) NSC

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LM2672 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

where:

= Soft-Start Current

:4.5 µA typical.

= Soft-Start Time

:Selected.

SSTH

= Soft-Start Threshold Voltage

:0.63V typical.

OUT

= Output Voltage

:Selected.

SCHOTTKY

= Schottky Diode Voltage Drop

:0.4V typical.

= Input Voltage

:Selected.

If this feature is not desired, leave this pin open.

7. Frequency Synchronization (optional)

The LM2672 (oscillator) can be synchronized to run with an

external oscillator, using the sync pin (pin 3). By doing so, the

LM2672 can be operated at higher frequencies than the

standard frequency of 260 kHz. This allows for a reduction in

the size of the inductor and output capacitor.

As shown in the drawing below, a signal applied to a RC filter at

the sync pin causes the device to synchronize to the frequency

of that signal. For a signal with a peak-to-peak amplitude of 3V

or greater,a1k

Ω resistor and a 100 pF capacitor are suitable

values.

7. Frequency Synchronization (optional)

For all applications, usea1k

Ω resistor and a 100 pF capacitor

for the RC filter.

INDUCTOR VALUE SELECTION GUIDES (For

Continuous Mode Operation)

01293429

FIGURE 4. LM2672-3.3

01293430

FIGURE 5. LM2672-5.0

LM2672 데이터시트(PDF) 13 Page - National Semiconductor (TI)

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