SC4612STRT datasheet(16/24 Pages) SEMTECH

16 / 24 page

 2007 Semtech Corp.

www.semtech.com

SC4612

POWER MANAGEMENT

that the stored charge on the bottom FET body diode will

be moved through the top FET as it starts to turn on. The

resulting power dissipation in the top FET will be:

OSC

⋅

To a first order approximation, it is convenient to only

consider conduction losses to determine FET suitability.

For a 5V in, 2.8V out at 14.2A requirement, typical FET

losses would be:

)

(

Ω))

(

1D2

Using 1.5X Room temp R

DS(ON) to allow for temperature rise.

BOTTOM FET - Bottom FET losses are almost entirely due

to conduction. The body diode is forced into conduction at

the beginning and end of the bottom switch conduction

period, so when the FET turns on and off, there is very little

voltage across it resulting in very low switching losses.

Conduction losses for the FET can be determined by:

)

(

)

(

COND

−

⋅

For the example above:

)

(

Ω)P

)

1D2

0D2

Each of the package types has a characteristic thermal

impedance, for the TO-220 package, thermal impedance

is mostly determined by the heatsink used. For the surface

mount packages on double sided FR4, 2 oz printed circuit

board material, thermal impedances of 40oC/W for the

D2PAK and 80oC/W for the SO-8 are readily achievable.

The corresponding temperature rise is detailed below:

(

)

It is apparent that single SO-8 Si4410 are not adequate for

this application, By using parallel pairs in each position,

power dissipation will be approximately halved and

temperature rise reduced by a factor of 4.

INPUT CAPACITORS - Since the RMS ripple current in the

input capacitors may be as high as 50% of the output

current, suitable capacitors must be chosen accordingly.

Also, during fast load transients, there may be restrictions

on input di/dt. These restrictions require useable energy

storage within the converter circuitry, either as extra output

capacitance or, more usually, additional input capacitors.

Choosing low ESR input capacitors will help maximize ripple

rating for a given size.

Application Information (Cont.)

SC4612STRT Datasheet(PDF) 16 Page - Semtech Corporation

SC4612STRT Datasheet(HTML) 16 Page - Semtech Corporation

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

Datasheet Download

Link URL