SC1402ISSTR View Datasheet(PDF) - Semtech Corporation

Part Name

Description

MFG CO.

SC1402ISSTR

Multi-Output, Low-Noise Power Supply Controller for Notebook Computers

Semtech Corporation 

Multi-Output, Low-Noise Power Supply

Controller for Notebook Computers

SC1402

December 15, 2000

Switching Losses Upper FET:

2A

High & Low IR IRF7901D1

Side FET’s Siliconix Si4412

3A

IR IRF7413

Siliconix Si4412

4A

IR IRF7805

Siliconix Si4410

PSU = CRSS

• VIN2

IG

• F • IOUT

=

240 • 10−12

• 122

1

• 300000 • 3

= 0.031W

Note: switching losses exist on the upper FET only

because the clamp diode across the lower FET will

turn on prior to the lower FET turning on.

Where Ig is the gate driver current. This is equal to

1A for the SC1402.

Input

Capacitor

Output

Capacitor

Resistor

Inductor

10uF, 30V Sanyo 2 X 10uF, 30V Sanyo 3 X 10uF, 30V Sanyo

OS-CON

OS-CON

OS-CON

330uF, 6.3V/10V* 2X 330uF, 6.3V/10V* 4X 330uF, 6.3V/10V*

AVX TPS

AVX TPS

AVX TPS

0.033Ω, Dale

0.02Ω, Dale

WSL2010-R033-F WSL2010-R020-F

0.012Ω, Dale

WSL2512-R012-F

15uF, Coilcraft

DO-3316P-153

10uF, Coilcraft

DO3316P-103

4.7uF, Coilcraft

DO3316P-472

Crss is the reverse transfer capacitance of the FET;

in this case it equals 240pF for the IRF7413.

So the total FET losses equate to:

*10V for 5V SMPS, 6.3V for 3V SMPS

Table 3

PFETS = 0.027+0.072+0.031 = 0.130W

Note that as Vin increases the power dissipation from

switching losses will also increase. This is especially

important if the input to the supply is from an AC

adapter. Therefore, it is necessary to check the cal-

culations with your maximum input voltage specifica-

tion. In addition, the distribution of power in the upper

and lower FET will change as input voltage in-

creases.

Other losses to consider are gate charge losses, in-

ductor switching and copper losses, and losses in the

input and output capacitors. All these items will de-

crease efficiency and need to be carefully analyzed to

obtain the highest efficiency possible, especially if

running off battery power.

Basic Application Circuit

The basic dual-output 3.3V / 5V synchronous buck

converter is shown in Figure 2. This circuit shows the

minimum requirements for successful operation. For

varying current levels, Table 3 provides a useful se-

lection of components for varying supply require-

ments and is based on the calculations described

previously. Input voltage ranges for all designs in the

table are 6.5V to 28V. Frequency used in calculations

is 300KHz.

© 2000 SEMTECH CORP.

14

652 MITCHELL ROAD NEWBURY PARK CA 91320

Share Link: