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LTC1430CN8

High Power Step-Down Switching Regulator Controller

Linear Technology 

LTC1430

APPLICATI S I FOR ATIO

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

devices. A typical SO-8 MOSFET with a RON suitable to

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.

SENSE+

LTC1430

FB

SENSE–

LTC1430 • F12

NC VOUT

R1

R2

NC

Figure 12. Using External Resistors to Set Output Voltages

4.7µF +

35V

C1

RC

220pF 7.5k

CC

4700pF

100Ω

0.1µF

GND

NC

VCC

PVCC2

PVCC1

G1

LTC1430

IMAX

NC

FREQSET IFB

SENSE+

SHDN

G2

COMP

SS

GND

CSS

0.01µF

FB

SENSE–

PGND

1µF

PGND

0.1µF

NC

GND

1N4148

5V

+ TOTAL

880µF

(220µF

10V × 4)

M1A*

M1B*

2.7µH/15A

3.3V

M2*

PGND

+ TOTAL

1980µF

(330µF

6.3V × 6)

* MOTOROLA MTD20N03HL

LTC1430 • F11

Figure 11. Typical Schematic Showing Layout Considerations

14

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