US3033

4-6

Rev. 1.5

1/14/99

Mode of Operation

L1

L2

D1 C4

C5

R1A

R1B

R2

R3

R4

R5

R6

R7

Switching

V

V

V

V

V

O

V

V

V

V

V

V

O

Linear

S

S

O

O

O

V

O

O

O

V

O

V

V

V = See parts list for value

S = Short

O = Open

TYPICAL APPLICATION

TYPICAL APPLICATION

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

Dual mode Operation between Switching or Linear mode.

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

R1A

Resistor

1

2.4k ohm,5%, SMT 1206 size

R1B

Resistor

1

22 ohm,5%, SMT 1206 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

R6

Resistor

1

180 ohm,1%, SMT 0805 size

R7

Resistor

1

100 ohm,1%, SMT 0805 size

R9

Resistor

1

10 ohm, 5%, SMT 1206 size

R10

Resistor

1

1k ohm, 5%, SMT 1206 size

R13

Resistor

1

7.5k ohm, 5%, SMT 1206 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

C9

Capacitor

1

470pF,Ceramic, SMT 0805 size

HS1

Heat Sink

1

For MOSFET in Switching mode , 577002

Aavid

For MOSFET in Linear mode :

507222 (3.3V current<5A),

576602 (3.3V current< 3.5A)

HS2

Heat Sink

1

For Schottky Diode , 577002

Aavid

3033app3-1.3

Vout

5V

C1

L1

C3

Q2

C2

L2

R4

C7

R6

R7

D1

R2

C4

R5

R1A

R1B

12V

R3

C5

C8

R9

1 2 3 4

5

6

7

8

Drv1V12swVfb1 Vhyst

Gnd

Vfb2

Drv2

V12

U1

R10

R13

C9

Figure3- This unique application of US3033 allows the de-

signer to switch between Linear or Switching mode of

operation using a single IC. This circuit has the flexibility

to be used for low current operation in Linear mode for

cost reasons and yet be able to operate in the Switching

mode if the load current increases and the heat gener-

ated by the Linear operation will be an issue. Table below

descibes the components that will be effected for the

two modes of operation.

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.