ncp1536 ON Semiconductor, ncp1536 Datasheet - Page 14

• Manufacturer Part Number: ncp1536
• Description: 3.0 A, Step-down Switching Regulator
• Manufacturer: ON Semiconductor

heat
improvements are needed, double sided or multilayer PC
boards with large copper areas should be considered. In
order to achieve the best thermal performance, it is highly
recommended to use wide copper traces as well as large
areas of copper in the printed circuit board layout. The only
exception to this is the OUTPUT (switch) pin, which should
not have large areas of copper (see page 5 ‘PCB Layout
Guideline’).
Thermal Analysis and Design
whether or not a heatsink will be required. First determine:
1. P
2. T
3. T
4. R
5. R
(Refer to Maximum Ratings on page 3 of this data sheet or
R
total power dissipated by the NCP1536:
where d is the duty cycle and for buck converter
I
V
Q
qJC
in
The following procedure must be performed to determine
The following formula is to calculate the approximate
conservative
D(max)
A(max
J(max)
qJC
qJA
and R
(quiescent current) and V
NCP1536 data sheet,
is minimum input voltage applied,
dissipation
)
qJA
P
maximum regulator power dissipation in the
application.
maximum ambient temperature in the
application.
maximum allowed junction temperature
(125°C for the NCP1536). For a
design, the maximum junction temperature
should not exceed 110°C to assure safe
operation. For every additional +10°C
temperature rise that the junction must
withstand, the estimated operating lifetime
of the component is halved.
package thermal resistance junction−case.
package thermal resistance junction−ambient.
values).
D
= (V
significantly.
in
d +
x I
Q
t on
T
) + d x I
+
sat
V
V
can be found in the
O
in
Load
,
If
x V
further
sat
thermal
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NCP1536
14
V
I
turn−off can be neglected if proper type catch diode is used.
Packages Not on a Heatsink (Free−Standing)
the junction temperature can be determined by the following
expression:
where (R
caused by the dissipated power and T
ambient temperature.
Packages on a Heatsink
the selected safe operating junction temperature determined
in step 3, than a heatsink is required. The junction
temperature will be calculated as follows:
where
selected safe operating junction temperature, then a larger
heatsink is required.
Some Aspects That can Influence Thermal Design
the junction temperature rise numbers are all approximate,
and there are many factors that will affect these numbers,
such as PC board size, shape, thickness, physical position,
location, board temperature, as well as whether the
surrounding air is moving or still.
area, copper thickness, single− or double−sided, multilayer
board, the amount of solder on the board or even color of the
traces.
board can also influence its effectiveness to dissipate the heat.
Load
O
The dynamic switching losses during turn−on and
For a free−standing application when no heatsink is used,
If the actual operating junction temperature is greater than
If the actual operating temperature is greater than the
It should be noted that the package thermal resistance and
Other factors are trace width, total printed circuit copper
The size, quantity and spacing of other components on the
is the regulator output voltage,
is the load current.
R
R
R
qJA
qJC
qCS
qSA
T
)(P
J
is the thermal resistance junction−case,
= P
is the thermal resistance case−heatsink,
is the thermal resistance heatsink−ambient.
D
) represents the junction temperature rise
D
T
J
(R
= (R
qJA
qJA
+ R
) (P
qCS
D
+ R
) + T
qSA
A
A
) + T
is the maximum
A