APPLICATION BULLETIN

AB-28

REV. 1.0.0

3

An integrated version of the opto-coupler (H11A817A) and

secondary voltage reference (RC431A) is also available

(FOD2712).

In the following sections we dive into some details of the

conversion from 12V and 5V down to final electronic load

voltage.

FAN5092 Two-Phase Interleaved

Buck Converter

The FAN5092 step-down (buck) converter is ideal for data

communications applications. This IC is a two-phase inter-

leaved buck converter switching up to 1MHz per phase. The

application diagram illustrates conversion from 12Vdown to

3.3V in a 12V-only input voltage source environment. The

chip integrates the controller and the drivers on a single die.

The high frequency of operation is enabled by:

• The monolithic approach of integrating controller and

drivers on board

• A fast proprietary “leading edge valley control”

architecture with 100ns of response time

• The strongest drivers in the industry at 1

Ω of source and

sink impedance for both high and low side driver of each

phase

Such combination of features, together with loss-less current

of power with very small passive components leading to new

record levels of power density.

The application diagram of the IC is shown in Fig 8 for a

3.3V, 30A load. Optimum companions of the FAN5092 are

the Fairchild discrete DMOS FDB6035AL for high side pass

transistors Q1,2 and FDB6676S for low side synchronous

rectification transistors Q2,4.

Two FAN5092 can be paralleled by means of doubling the

above application and connecting together two pins (pin 26

and pin 15). This will allow handling of loads up to 120A.

Fig. 8. FAN5092 Application Circuit

+12V

+12V

+12V

+12V

+12V

+12V

3.3V

30A

R16

R17

ENABLE/SS

PWRGD

+12V

D1

D2

C2

C1

C3

R1

R4

R2

R7

R8

R3

A

1 2

3

4 5 6 7 8 9 10 11 12 13 14

28 27 26 25 24 23 22 21 20 19 18 17 16 15

+5V

D3

C5

R5

Q1

Q3

Q4

L2

L3

X

L1 (Optional)

U1

FAN5092

Q2

D3=8.2V

R6

C4