SC1402(2001) View Datasheet(PDF) - Semtech Corporation

Part Name

Description

Manufacturer

SC1402
(Rev.:2001)

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

Semtech Corporation 

SC1402

POWER MANAGEMENT

Application Information (Cont.)

Conduction Losses Upper FET:

PCU = R DS D I2

PCU = 0.011

3.3

12

32 = 0.027W

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 calculations with your maximum input

voltage specification. In addition, the distribution of power in

the upper and lower FET will change as input voltage increases.

Conduction Losses Lower FET:

PCL = R DS (1 − D) I2

PCL = 0.011

1 −



3.3

12





32 = 0.072W

Other losses to consider are gate charge losses, inductor

switching and copper losses, and losses in the input and output

capacitors. All these items will decrease efficiency and need

to be carefully analyzed to obtain the highest efficiency

possible, especially if running off battery power.

Basic Application Circuit

Switching Losses Upper FET:

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

PSU = CRSS

• VIN2 • F • IOUT

IG

=

240

• 10−12

• 122

1

•

300000

•

3

=

0.031W

is shown on page 16. This circuit shows the minimum

requirements for successful operation. For varying current

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.

levels, Table 3 provides a useful selection of components for

varying supply requirements 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.

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:

PFETS = 0.027+0.072+0.031 = 0.130W

2A

High & Low

Side FETs

IR IRF7901D1

Siliconix Si4412

Input Capacitor

10µF, 30V

Sanyo OS-CON

Output Capacitor 330µF, 6.3V/10V*

AVX TPS

Resistor

0.033 ohm, Dale

WSL2010-R033-F

Inductor

15µF, Coilcraft

DO-3316P-153

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

3A

IR IRF7413

Siliconix Si4412

2 X 10µF, 30V

Sanyo OS-CON

2 X 330µF, 6.3V/10V*

AVX TPS

0.02 ohm, Dale

WSL2010-R020-F

10µF, Coilcraft

DO3316P-103

4A

IR IRF7805

Siliconix Si4410

3 X 10µF, 30V

Sanyo OS-CON

4 X 330µF, 6.3V/10V*

AVX TPS

0.12 ohm, Dale

WSL2512-R012-F

4.7µF, Coilcraft

DO3316P-472

Table 3

 2001 Semtech Corp.

15

www.semtech.com

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