US3033

4-7

Rev. 1.5

1/14/99

Figure4- The circuit in figure 4 is the application of the US3033 in a switching mode only. This circuit can be used to

generate a low cost 5V to 3.3V for either Pentium application with AGP socket or in Pentium II applications where it is desirable to

generate an accurate on board 3.3V supply.

TYPICAL APPLICATION

TYPICAL APPLICATION

5V to 3.3V for Pentium Application with AGP or Pentium II Application without ATX power supply

Switching mode Operation.

Ref Desig

Description

Qty

Part #

Manufacturer

U1

LDO/Switcher IC

1

US3033CS ( 8 pin SOIC)

Unisem

Q2

MOSFET

1

IRL3303 (TO220)

International

IRL3103S (TO263)

(note 1)

Rectifier

D1

Schottky Diode

1

MBR1045CT (TO220)

MBRB1545CT (TO263) (note1)

Motorola

L2

Inductor

1

Core:T50-18,L=4 uH

Micro Metal

Turns: 10T, 18 AWG

(core)

L1

Inductor

1

L=2 uH

R1

Resistor

1

22 ohm,5%, SMT 1206 size

R9

Resistor

1

10 ohm,5%, SMT 0805 size

R2

Resistor

1

10 ohm, 5%, SMT 1206 size

R3

Resistor

1

249 kohm,1%, SMT 0805 size

R4

Resistor

1

1 kohm,1%, SMT 0805 size

R5

Resistor

1

576 ohm,1%, SMT 0805 size

C1,2

Capacitor

2

6MV1500GX, 1500uF,6.3V, Elect

Sanyo

C3

Capacitor

1

1 uF,Ceramic, SMT 0805 size

C4

Capacitor

1

470 pF,Ceramic, SMT 0805 size

Sanyo

C5

Capacitor

1

10 pF,Ceramic, SMT 0805 size

Sanyo

C7

Capacitor

1

6MV1500GX, 1500uF,6.3V, Elect

Sanyo

C8

Capacitor

1

1 uF,Ceramic, SMT 0805 size

HS1

Heat Sink

1

For MOSFET , 577002

Aavid

HS2

Heat Sink

1

For Schottky Diode , 577002

Aavid

Note 1: For the applications where it is desirable to eliminate the heat sink, the IRL3103S for Q2 and MBR1545CT for D2 in TO263

packages with minimum of 1" square copper pad can be used.

3033app4-1.2

Vout

5V

C1

L1

C3

Q2

C2

L2

R4

C7

D1

R2

C4

R5

R1

12V

R3

C5

C8

R9

1

2

3

4

5

6

7

8

Drv1V12swVfb1 Vhyst

Gnd

Vfb2

Drv2

V12

U1