MC33288 Просмотр технического описания (PDF) - Motorola => Freescale
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MC33288 Datasheet PDF : 8 Pages
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Freescale Semiconductor, Inc.
MC33288
Soldering Information
This device is packaged in a Surface Mount Power
package indended to be soldered directly on the Printed
Circuit Board.
This device was qualified according to JEDEC standards
JESD22-A113-B and J-STD-020A with the reflow conditions
applicable for packages with thickness above 2.5mm :
Convection 220°C +5/-0°C
VPR 215-219°C
IR / Convection 220°C +5/-0°C
The maximum peak temperature during the soldering process
should not exceed 220°C (+5°C/-0°C). The time at maximum
temperature should range from 10 to 40s max.
Thermal Management
The junction to case thermal resistance is 2°C/W
maximum. The junction to ambient thermal resistance is
dependent on the mounting technology and the addition of
heat sink. One of the most commonly used mounting
technique consists in using the printed circuit board and the
copper lines as heat sink.
Figure 1. Printed Board Layout Example (not to scale)
Down side pcb
8 cm2
Top side pcb
2 cm2
Figure 2. Simplified Thermal Model (Electrical Equivalent)
Chan 1 Junction
Temp Node
(Volts represent Die
Surface Temperature)
Temp Node
Chan 2 Junction
Chan 1
Switch
Chan 2
Switch
Rthjc1
2°C/W
Chan 1
Power (W)
(1.0A=1W of
Power Dissipation)
Rthca
(1.0Ω=1°C/W)
25°C/W
Rthjc2
2°C/W
Chan 2
Power (W)
Case Temp Node
Ambient Temp Node
(1.0V=1°C)
AmbientTemperature
Transient Thermal Model
A more complete model including thermal capacitance is
proposed in figure 3.
Figure 3. Transient thermal model
HSOP20
Thermal
via from
top to down
side pcb
external pcb (4x4 cm)
Figure 1 shows an example of printed circuit board layout.
It has a total of 10cm2 additional copper on two sides (2.5 cm2
on the top side and 7.5 cm2 on the down side).
With the above layout, thermal resistance junction to ambient
of 25°C/W can be achieved, this value being splitted into :
• junction to case : Rthjc1 = Rthjc2 = 2°C/W
• case to ambient : Rthca = 23 °C/W.
Lower value can be reached with the help of larger and
thicker copper metal, higher number of thermal via from top to
down side pcb and the use of additional thermal via from the
circuit board to the module case.
Steady State Thermal Model
The junction to ambient thermal resistance of the circuit
mounted on a printed circuit board can be splitted into two
main parts : junction to case and case to ambient resistances.
A simplified steady state model is shown in figure 2.
5mJ/K
5mJ/K
MOS1 3K/W
1mJ/K
4mJ/K
MOS2 MOS3 3.5K/W
Control
3K/W
450K/W
3K/W
Case
3.5K/W
0.5J/K
Ambiant
3K/W
Board
20K/W
6J/K
300K/W
This gives a thermal impedance versus time (figure 4), which
has been determined with the printed circuit board shown in
figure 1.
Figure 4. Junction to ambiant Thermal impedance
30
20
10
0
0
100
200
300 400
500
600 700 800
Time (sec.)
This figure shows that the steady state is reached after about
10 minutes. It also clearly shows that the device can dissipate
almost twice the power within one minute compared to the
maximum allowed power dissipation in steady state.
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