14

LTC1430

S

APPLICATI

I FOR ATIO

Figure 11. Typical Schematic Showing Layout Considerations

R1

NC

NC

R2

LTC1430 • F12

LTC1430

FB

Figure 12. Using External Resistors to Set Output Voltages

+

+

+

LTC1430 • F11

3.3V

2.7

µH/15A

TOTAL

1980

µF

(330

µF

6.3V

×6)

M1A*

M2*

FREQSET

GND

PGND

SHDN

COMP

NC

SS

PGND

GND

7.5k

0.1

µF

1

µF

0.1

µF

4700pF

C1

220pF

0.01

µF

4.7

µF

35V

100

Ω

G1

G2

FB

NC

NC

LTC1430

GND

PGND

* MOTOROLA MTD20N03HL

1N4148

5V

M1B*

TOTAL

880

µF

(220

µF

10V

×4)

power inductor will generally be the most massive single

component on the board; it can require a mechanical hold-

down in addition to the solder on its leads, especially if it

is a surface mount type.

The power MOSFETs used require some care to ensure

proper operation and reliability. Depending on the current

levels and required efficiency, the MOSFETs chosen may

be as large as TO-220s or as small as SO-8s. High

efficiency circuits may be able to avoid heat sinking the

power devices, especially with TO-220 type MOSFETs. As

an example, a 90% efficient converter working at a steady

3.3V/10A output will dissipate only (33W/90%) • 10% =

3.7W. The power MOSFETs generally account for the

majority of the power lost in the converter; even assuming

that they consume 100% of the power used by the

converter, that’s only 3.7W spread over two or three

provide 90% efficiency in this design can commonly

dissipate 2W when soldered to an appropriately sized

piece of copper trace on a PC board. Slightly less efficient

or higher output current designs can often get by with

standing a TO-220 MOSFET straight up in an area with

some airflow; such an arrangement can dissipate as much

as 3W without a heat sink. Designs which must work in

high ambient temperatures or which will be routinely

overloaded will generally fare best with a heat sink.