AN1139 STMicroelectronics, AN1139 Datasheet - Page 46

• Manufacturer Part Number: AN1139
• Description: L6254 - L6268 - L6269 12V DISK DRIVE POWER COMBO IC
• Manufacturer: STMicroelectronics

AN1139 APPLICATION NOTE
free air convention flow).
In steady state condition (stable running dissipation Spindle + Vcm) the Junction Temperature increase is in the
range of 20-25×°C maximum.
For the transient behaviour, up to 3 seconds (spindle Spin-Up) the board dimension are not so important as,
within this time, almost all the heat is still inside the package. In this case the key parameters to identify the
transient thermal impedance are the die size, the dissipating area, the package geometry. Under the condition
of this example, the thermal impedance @3sec is about 18×°C/W. This means tha at 3 seconds of Spin -Up,
the temperature increase is between 35 to 40×°C.
In conclusion, the Spin-Up phase induces a temperature increase for the junction of about 35-40×°C; after that
when the steady state running will take place the Junction Temperature will go down and will stabilize around
20-25×°C. To have the absolute Junction Temperature, simply add the ambient temperature.
7.3
The L6268 device provides a piece of metal (SLUG) mounted on the back of the package. This metal, melted
in the plastic of the package is designed to handle higher power dissipation by lowering the Junction to ambient
thermal resistance. When the slug is soldered to the PCB, the Rthj-a is 30 to 35×°C/W.
The Slug is not available on the L6254 and L6269 devices. Following in Figure #30 is outlined the Slug dimen-
sion.
Figure 30. TQFP with SLUG, Package Outline
The Figure #31 shows rhe suggested pattern to sold the device slug to the drive board. Figure #32 depicts the
design and dimension of the Slug mounted on the back of the TQFP44 package.
Figure #33 shows the device temperature rise with and without Slug.
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Dimensions Tolerances
SLUG
K(deg.)
D1
D3
A1
A2
E1
E3
S1
S2
L1
A
D
E
B
C
H
L
e
+/-0.05
+/-0.05
+/-0.20
+/-0.10
+/-0.20
+/-0.10
+/-0.15
+/-0.05
(mm)
Max.
Typ.
Typ.
Typ.
Typ.
Max.
Typ.
Typ.
Typ.
8.00
8.00
0.80
0.35
44
Lead Count
12.00
10.00
12.00
10.00
0°-7°
1.60
0.10
1.40
0.60
1.00
0.20
6.00
6.00
5.90
7.50
7.50
0.50
0.23
64
E3
E1
S1
E
H
A1
C
A2
A