SC1403ITSTRT datasheet(13/31 Pages) SEMTECH

13 / 31 page

 2004 Semtech Corp.

SC1403

POWER MANAGEMENT

United States Patent No. 6,377,032

www.semtech.com

Applications Information

Applications Information (Cont.)

GATE

⋅

Cg is the effective gate capacitance, equal to the Total Gate Charge

divided by VGS from the vendor datasheet, and is 7.9nF for the

IRF7413. V in the above formula is the final gate-source voltage

on the mosfet, 5V for the SC1403.

The total mosfet losses is the sum of the three loss components.

GATE

SWITCHING

CONDUCTION

DISS

TOTAL

The mosfet dissipation under conditions of 15V input, 6A load,

and ambient temperature of 25C, can be determined as:

DNOM = 0.22

∆IL = 1.26A

IMIN = 5.37A

IMAX = 6.63A

IRMS = 4.88A

Rds(on) (100C) = 18 mohm

PCONDUCTION = 429mW

PSWITCHING = 97mW

PGATE = 30mW

PTOTAL_DISS = 429 + 97 + 30 = 556 mW

The junction temperature rise resulting from the power dissipation

is calculated as:

⋅

∆

T is the total device dissipation, and θJA is the package thermal

resistance, which is 50°C/W for the IRf7413. The junction tem-

perature rise is then:

∆T

J = 0.556W

50°C/W = 27.8°

This is a modest temperature rise, so no special heat sinking is

required when laying out the mosfet.

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