PRODUCT SPECIFICATION

RC5033

10

Dual Power Supply Application

In some CPU power applications there may be a need for a

split voltage converter. The circuit in Figure 4 addresses this

need with only minimal component count. The basic

RC5033 non-synchronous DC-DC converter is augmented

with an op-amp, a power MOSFET, and some 1% resistors

to provide a dual power supply with one voltage set to 3.3V

and the other, slaved off of the 3.3V, set to 2.9V. In this con-

figuration, the RC5033 converts the 5V to 3..3V with high

efficiency. By using the op-amp, power FET, and the resis-

tors, a low-dropout linear regulator is realized that can be run

off of the 3.3V. The 2.9V linear regulator has a relatively

high efficiency just due to the fact that the ratio of 2.9V/3.3V

is close to 88%. The power FET is a low Rdson n-channel

MOSFET, and thus it is reasonably inexpensive. The opamp

can be a garden variety, though the input bias current and

output slew rate need to be considered to optimize accuracy

and transient response. The overall efficiency of this power

supply system will very much depend upon the percentage of

power used on each power output. Overall, the efficiency of

this system will be lower than if both supplies were imple-

mented as switchers; however, the added savings of the part

count reduction may more than compensate for the overall

lower efficiency.

Standard Application Circuit

The circuit shown in Figure 1 along with its components and

values has been designed as representative of the typical

application involving the RC5033 for a Pentium™ CPU. Use

of the standard application circuit will deliver the perfor-

mance curves shown under the Typical Operating Character-

istics section of the data sheet. Many users will want to

develop their own DC-DC converter solution that is uniquely

tailored to a specific application requirement. In that case,

the users should review the detailed information in the

Design Procedure and Applications Information section of

the data sheet.

Detailed Description

The RC5033 is a programmable voltage synchronous con-

troller. When designed around the appropriate external com-

ponents, it can be configured to deliver more than 10A of

output current. During heavy loading conditions the RC5033

functions as a current-mode PWM step down regulator.

Under light loading conditions, the regulator functions in the

PFM or pulse skipping mode, thereby increasing its effi-

ciency under light loads.

Applications Discussion

VCCP

C5

200

µF

DS2

EC10QS02

RC5033

9

10

11

12

C13

4.7

µF

13

14

8

7

6

5

4

3

2

1

15

16

GND

C4

0.1

µF

+12V

C1

47pF

R2

12K

R3

88K

LM308A

–

+

+

–

M1

MTD20N03HDL

DS1

MBRB1545CT

C9

330

µF

65-5033-08

C2

1

µF

L1

1.5

µH

R1

0.012

Ω

VO

M2

MTD20N03HDL

VO2

2.9V

C1

47pF