NCN51206GEVB Datasheet, PDF (54/55 Pages) ON Semiconductor – Transceiver for KNX Twisted Pair Networks

NCN5120
PACKAGE THERMAL CHARACTERISTICS
The NCN5120 is available in a QFN40 package. For cooling optimizations, the QFN40 has an exposed thermal pad which
has to be soldered to the PCB ground plane. The ground plane needs thermal vias to conduct the heat to the bottom layer.
Figure 59 gives an example of good heat transfer. The exposed thermal pad is soldered directly on the top ground layer (left
picture of Figure 59). It‘s advised to make the top ground layer as large as possible (see arrows Figure 59). To improve the heat
transfer even more, the exposed thermal pad is connected to a bottom ground layer by using thermal vias (see right picture of
Figure 59). It‘s advised to make this bottom ground layer as large as possible and with as less as possible interruptions.
For precise thermal cooling calculations the major thermal resistances of the device are given (Table 4). 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 exposed pad)
The major thermal resistances of the device are the Rth from the junction to the ambient (Rth_ja) and the overall Rth from
the junction to exposed pad (Rth_jp). In Table 4 one can find the values for the Rth_ja and Rth_jp, simulated according to JESD−51.
The Rth_ja for 2S2P is simulated conform JEDEC JESD−51 as follows:
− A 4−layer 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
− The 2 power internal planes: 36 mm thick copper with an area of 5500 mm² copper and 90% conductivity
The Rth_ja for 1S0P is simulated conform to JEDEC JESD−51 as follows:
− A 1−layer 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
Figure 59. PCB Ground Plane Layout Condition (left picture displays the top ground layer, right picture displays
the bottom ground layer)
ORDERING INFORMATION
Device Number
NCN5120MNG
Temperature Range
−25°C to 85°C
Package
QFN−40
(Pb−Free)
Shipping^†
50 Units / Tube
100 Tubes / Box
NCN5120MNTWG
−25°C to 85°C
QFN−40
(Pb−Free)
3000 / Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specification Brochure, BRD8011/D.
www.onsemi.com
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