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AMIS-30622_13 Datasheet, PDF (5/50 Pages) ON Semiconductor – I2C Micro-Stepping Motor Driver | |||
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AMISâ30622
PACKAGE THERMAL RESISTANCE
The AMISâ30622 is available in SOICâ20 or optimized
NQFPâ32 packages. For cooling optimizations, the NQFP
has an exposed thermal pad which has to be soldered to the
PCB ground plane. The ground plane needs thermal vias to
conduct the head to the bottom layer. Figures 3 and 4 give
examples for good power distribution solutions.
For precise thermal cooling calculations the major
thermal resistances of the devices are given. The thermal
media to which the power of the devices has to be given are:
⢠Static environmental air (via the case)
⢠PCB board copper area (via the device pins and
exposed pad)
The thermal resistances are presented in Table 5: DC
Parameters.
The major thermal resistances of the device are the Rth
from the junction to the ambient (Rthja) and the overall Rth
from the junction to the leads (Rthjp).
The NQFP device is designed to provide superior thermal
performance. Using an exposed die pad on the bottom
surface of the package is mainly contributing to this
performance. In order to take full advantage of the exposed
pad, it is most important that the PCB has features to conduct
heat away from the package. A thermal grounded pad with
thermal vias can achieve this.
In the table below, one can find the values for the Rthja and
Rthjp, simulated according to the JESDâ51 norm:
Package
SOICâ20
NQFPâ32
Rth
JunctionâtoâLeads and
Exposed Pad â Rthjp
0,95
Rth
JunctionâtoâLeads
Rthjp
19
The Rthja for 2S2P is simulated conform to JESDâ51 as
follows:
⢠A 4âlayer printed circuit board with inner power planes
and outer (top and bottom) signal layers is used
⢠Board thickness is 1.46 mm (FR4 PCB material)
⢠The 2 signal layers: 70 mm thick copper with an area of
5500 mm2 copper and 20% conductivity
ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ
Figure 3. Example of SOICâ20 PCB Ground Plane
Layout (preferred layout at top and bottom)
Rth
JunctionâtoâAmbient
Rthja (1S0P)
Rth
JunctionâtoâAmbient
Rthja (2S2P)
62
39
60
30
⢠The 2 power internal planes: 36 mm thick copper with
an area of 5500 mm2 copper and 90% conductivity
The Rthja for 1S0P is simulated conform to JESDâ51 as
follows:
⢠A 1âlayer printed circuit board with only 1 layer
⢠Board thickness is 1.46 mm (FR4 PCB material)
⢠The layer has a thickness of 70 mm copper with an area
of 5500 mm2 copper and 20% conductivity
ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃNQFÃÃÃÃÃÃÃPâ3ÃÃÃÃÃÃÃÃÃÃ2 ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ
Figure 4. Example of NQFPâ32 PCB Ground Plane
Layout (preferred layout at top and bottom)
http://onsemi.com
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