Thermal characteristics
12 Thermal characteristics
STM8S105x4/6
The maximum junction temperature (TJmax) of the device must never exceed the values
specified in Table 18: General operating conditions, otherwise the functionality of the device
cannot be guaranteed.
The maximum junction temperature TJmax, in degrees Celsius, may be calculated using the
following equation:
TJmax = TAmax + (PDmax x ï‘JA)
Where:
ï‚· TAmax is the maximum ambient temperature in ï‚°C
ï‚· ï‘JA is the package junction-to-ambient thermal resistance in ï‚°ï€ C/W
ï‚· PDmax is the sum of PINTmax and PI/Omax (PDmax = PINTmax + PI/Omax)
ï‚· PINTmax is the product of IDD and VDD, expressed in Watts. This is the maximum chip
internal power.
ï‚· PI/Omax represents the maximum power dissipation on output pinsï€
Where:ï€
PI/Omax = ï“ï€ (VOL*IOL) + ï“((VDD-VOH)*IOH), ï€
taking into account the actual VOL/IOL and VOH/IOH of the I/Os at low and high level in
the application.
Table 56. Thermal characteristics(1)
Symbol
Parameter
Value
Thermal resistance junction-ambientï€
LQFP48 - 7x7 mm
Thermal resistance junction-ambientï€
LQFP44 - 10x10 mm
ï‘JA
Thermal resistance junction-ambientï€
LQFP32 - 7x7 mm
Thermal resistance junction-ambientï€
UFQFPN32 - 5x5 mm
Thermal resistance junction-ambientï€
SDIP32 - 400 ml
1. Thermal resistances are based on JEDEC JESD51-2 with 4-layer PCB in a natural convection
environment.
Unit
°C/W
12.1
Reference document
JESD51-2 integrated circuits thermal test method environment conditions - natural
convection (still air). Available from www.jedec.org.
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