LTC1430A Ver la hoja de datos (PDF) - Linear Technology
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LTC1430A Datasheet PDF : 24 Pages
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APPLICATI S I FOR ATIO
LTC1430A
+
4.7µF
35V
C1
RC
220pF 7.5k
CC
4700pF
100Ω
0.1µF
GND
NC
VCC
PVCC2
PVCC1
G1
LTC1430A
IMAX
NC
FREQSET IFB
SENSE+
SHDN
G2
COMP
SS
GND
CSS
0.01µF
FB
SENSE–
PGND
1µF
PGND
0.1µF
NC
GND
5V
MBR0530T1
+ TOTAL
880µF
(220µF
10V × 4)
Q1A*
Q1B*
2.7µH/15A
3.3V
Q2*
PGND
+ TOTAL
1980µF
(330µF
6.3V × 6)
* MOTOROLA MTD20N03HL
1430 F14
Figure 14. Typical Schematic Showing Layout Considerations
SENSE+
LTC1430A
FB
SENSE–
1430 F15
NC VOUT
R1
R2
NC
Figure 15. Using External Resistors to Set Output Voltages
be floated and an external resistor string should be con-
nected to FB (Figure 15). As before, connect the top
resistor (R1) to the output as close to the load as practical
and connect the bottom resistor (R2) to the common
GND/PGND point. In both cases, connecting the top of the
resistor divider (either SENSE + or R1) close to the load can
significantly improve load regulation by compensating for
any drops in PC traces or hookup wires between the
LTC1430A and the load.
Power Component Hook-Up/Heat Sinking
As current levels rise much above 1A, the power compo-
nents supporting the LTC1430A start to become physi-
cally large (relative to the LTC1430A, at least) and can
require special mounting considerations. Input and output
capacitors need to carry high peak currents and must have
low ESR; this mandates that the leads be clipped as short
as possible and PC traces be kept wide and short. The
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.
17
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