HUF76113SK8T データシートの表示（PDF） - Intersil
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HUF76113SK8T Datasheet PDF : 11 Pages
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HUF76113SK8
Thermal Resistance vs. Mounting Pad Area
The maximum rated junction temperature, TJ(MAX), and the
thermal resistance of the heat dissipating path determines
the maximum allowable device power dissipation, PD(MAX),
in an application. Therefore the application’s ambient
temperature, TA (oC), and thermal resistance RθJA (oC/W)
must be reviewed to ensure that TJ(MAX) is never exceeded.
Equation 1 mathematically represents the relationship and
serves as the basis for establishing the rating of the part.
PDMAX = (---T----J---M---Z---A-θ---X-J---A--–----T----A-----)
(EQ. 1)
In using surface mount devices such as the SO-8 package,
the environment in which it is applied will have a significant
influence on the part’s current and maximum power
dissipation ratings. Precise determination of the PD(MAX) is
complex and influenced by many factors:
1. Mounting pad area onto which the device is attached and
whether there is copper on one side or both sides of the
board
2. The number of copper layers and the thickness of the
board
3. The use of external heat sinks
4. The use of thermal vias
5. Air flow and board orientation
6. For non steady state applications, the pulse width, the
duty cycle and the transient thermal response of the part,
the board and the environment they are in.
Intersil provides thermal information to assist the designer’s
preliminary application evaluation. Figure 23 defines the
RθJA for the device as a function of the top copper
(component side) area. This is for a horizontally positioned
FR-4 board with 1oz copper after 1000 seconds of steady
state power with no air flow. This graph provides the
necessary information for calculation of the steady state
junction temperature or power dissipation. Pulse
applications can be evaluated using the Intersil device Spice
thermal model or manually utilizing the normalized maximum
transient thermal impedance curve.
250
RθJA = 79.3 - 21.8*ln(AREA)
200
177 oC/W - 0.0115in2
143 oC/W - 0.054in2
150
100
50
0.001
0.01
0.1
1.0
AREA, TOP COPPER AREA (in2)
FIGURE 23. THERMAL RESISTANCE vs MOUNTING PAD AREA
Displayed on the curve are the three RθJA values listed in
the Electrical Specifications table. The three points where
chosen to depict the compromise between the copper board
area, the thermal resistance and ultimately the power
dissipation, PD(MAX). Thermal resistances corresponding to
other component side copper areas can be obtained from
Figure 23 or by calculation using Equation 2. The area, in
square inches is the top copper area including the gate and
source pads.
RθJA = 79.3 – 21.8 × ln (Area)
(EQ. 2)
8
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