LTC1430 LINER [Linear Technology], LTC1430 Datasheet - Page 14

• Manufacturer Part Number: LTC1430
• Description: High Power Step-Down Switching Regulator Controller
• Manufacturer: LINER [Linear Technology]

LTC1430
A
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
14
PPLICATI
O
4700pF
C1
220pF
U
4.7 F
C
35V
C
S
+
R
7.5k
I FOR ATIO
C
U
GND
NC
NC
C
0.01 F
Figure 11. Typical Schematic Showing Layout Considerations
0.1 F
SS
GND
Figure 12. Using External Resistors to Set Output Voltages
W
I
FREQSET
SHDN
COMP
SS
MAX
GND
V
CC
LTC1430
100
SENSE
SENSE
PV
PGND
PV
CC2
CC1
G1
I
G2
FB
FB
U
+
–
LTC1430
PGND
SENSE
SENSE
NC
LTC1430 • F12
1 F
FB
+
–
0.1 F
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 R
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.
NC
NC
V
OUT
1N4148
R1
R2
M1A*
* MOTOROLA MTD20N03HL
5V
M2*
PGND
M1B*
+
2.7 H/15A
TOTAL
880 F
(220 F
10V 4)
+
LTC1430 • F11
TOTAL
1980 F
(330 F
6.3V 6)
3.3V
ON
suitable to