LM3478MASLASHNOPB datasheet(26/43 Pages) TI2

26 / 43 page

RSEN =

VSENSE - D(VSL + 'VSL)

ISWPEAK

'VOUT =

IOUT

1-D +

'IL2

(

) ESR

LM3478

SNVS085X – JULY 2000 – REVISED DECEMBER 2017

www.ti.com

Product Folder Links: LM3478

Submit Documentation Feedback

Typical Applications (continued)

(46)

IL1PK must be lower than the maximum current rating set by the current sense resistor.

The value of L1 can be increased above the minimum recommended to reduce input ripple and output ripple.

However, once DIL1 is less than 20% of IL1AVE, the benefit to output ripple is minimal.

By increasing the value of L2 above the minimum recommended, ΔIL2 can be reduced, which in turn will reduce

the output ripple voltage:

(47)

where ESR is the effective series resistance of the output capacitor.

If L1 and L2 are wound on the same core, then L1 = L2 = L. All of the previous equations will hold true if the

inductance is replaced by 2L.

8.2.2.2.4

Sense Resistor Selection

The peak current through the switch, ISW(PEAK) can be adjusted using the current sense resistor, RSEN, to provide

a certain output current. Resistor RSEN can be selected using Equation 48

(48)

8.2.2.2.5

Sepic Capacitor Selection

The selection of the SEPIC capacitor, CS, depends on the RMS current. The RMS current of the SEPIC

capacitor is given by Equation 49.

(49)

The SEPIC capacitor must be rated for a large ACrms current relative to the output power. This property makes

the SEPIC much better suited to lower power applications where the RMS current through the capacitor is

relatively small (relative to capacitor technology). The voltage rating of the SEPIC capacitor must be greater than

the maximum input voltage. There is an energy balance between CS and L1, which can be used to determine

the value of the capacitor. Equation 50 shows the basic energy balance.

(50)

where

(51)

is the ripple voltage across the SEPIC capacitor, and

(52)

is the ripple current through the inductor L1. The energy balance equation can be solved using Equation 53 to

provide a minimum value for CS.

(53)

LM3478MA/NOPB Datasheet(PDF) 26 Page - Texas Instruments

LM3478MA/NOPB Datasheet(HTML) 26 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Datasheet Download

Link URL