APPLICATION NOTE

AN53

5

In general, a higher operating frequency decreases the peak

ripple current flowing in the output inductor, thus allowing

the use of a smaller inductor value. operation at higher fre-

quencies also decreases the amount of energy storage that

must be provided by the bulk output capacitors during load

transients.

Unfortunately, the efficiency losses due to switching of the

MOSFETs increase as the operating frequency is increased.

Thus, efficiency is optimized at lower operating frequencies.

An operating frequency of 300 kHz was chosen in this

Application Note to optimize efficiency while maintaining

excellent regulation and transient performance under all

operating conditions.

Design Considerations and Component

Selection

Figure 3 illustrates a synchronous application using the

RC5051.

Figure 3. Synchronous DC-DC Converter Application Schematic Using the RC5051

VID3

VID2

VID1

VID0

8

7

6

5

4

3

2

1

9

10

11

12

13

14

15

16

17

18

19

20

+5V

PWRGD

RC5051

VCC

ENABLE

C7

0.1

mF

C8

0.1

mF

10K

½

C3

0.1

mF

R1

C5

1

mF

L1

2.5

mH

VREF

C1

C2

0.1

mF

0.1

mF

+12V

VID4

R4

100pF

65-5051-03

*Refer to Table 3 for values of

VO

D2

1N5820

L2

2.3

µH

4.7

½

Q2

Q1

D1

1N4735A

C6

0.1

mF

1

mF

4.7

½

47

½

R2

R3

C4