LM2671M-3.3 datasheet(14/31 Pages) TI

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LM2671

SNVS008K – SEPTEMBER 1998 – REVISED APRIL 2013

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PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

where:

ISS = Soft-Start Current :4.5 μA typical.

tSS = Soft-Start Time :Selected.

VSSTH = Soft-Start Threshold Voltage :0.63V typical.

VOUT = Output Voltage :Selected.

VSCHOTTKY = Schottky Diode Voltage Drop :0.4V typical.

VIN = Input Voltage :Selected.

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

softstart capacitor values and operating conditions, the LM2671 can

exhibit an overshoot on the output voltage during turn on. Especially

when starting up into no load or low load, the softstart function may

not be effective in preventing a larger voltage overshoot on the

output. With larger loads or lower input voltages during startup this

effect is minimized. In particular, avoid using softstart capacitors

between 0.033µF and 1µF.

7. Frequency Synchronization (optional)

The LM2671 (oscillator) can be synchronized to run with an external

For all applications, use a 1 k

Ω resistor and a 100 pF capacitor for

oscillator, using the sync pin (pin 3). By doing so, the LM2671 can

the RC filter.

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, a

1 k

Ω resistor and a 100 pF capacitor are suitable values.

INDUCTOR VALUE SELECTION GUIDES

(For Continuous Mode Operation)

Figure 24. LM2671-3.3

Figure 25. LM2671-5.0

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