STM8S105C4B3 datasheet(116/127 Pages) STMICROELECTRONICS

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Unit

Value

Parameter

Symbol

°C/W

Thermal resistance junction-ambient

LQFP 32 - 7 x 7 mm

ΘJA

°C/W

Thermal resistance junction-ambient

VQFPN 32 - 5 x 5 mm

ΘJA

1. Thermal resistances are based on JEDEC JESD51-2 with 4-layer PCB in a natural

convection environment.

Reference document

11.3.1

JESD51-2 integrated circuits thermal test method environment conditions - natural convection

(still air). Available from www.jedec.org.

Selecting the product temperature range

11.3.2

When ordering the microcontroller, the temperature range is specified in the order code.

The following example shows how to calculate the temperature range needed for a given

application.

Assuming the following application conditions:

• Maximum ambient temperature TAmaz = 82 °C (measured according to JESD51-2)

• IDDmax = 15 mA, VDD = 5.5 V

• Maximum 8 standard I/Os used at the same time in output at low level with IOL = 10 mA,

VOL= 2 V

• Maximum 4 high sink I/Os used at the same time in output at low level with IOL = 20 mA,

VOL= 1.5 V

• Maximum 2 true open drain I/Os used at the same time in output at low level with IOL =

20 mA, VOL= 2 V

PINTmax = 15 mA x 5.5 V = 82.5 mW

PIOmax = (10 mA x 2 V x 8 )+(20 mA x 2 V x 2)+(20 mA x 1.5 V x 4) = 360 mW

This gives: PINTmax = 82.5 mW and PIOmax 360 mW:

PDmax = 82.5 mW + 360 mW

Thus: PDmax = 443 mW

TJmax for LQFP32 can be calculated as follows, using the thermal resistance ΘJA :

TJmax = 75° C + (59° C/W x 464 mW) = 75°C + 27°C = 102° C

This is within the range of the suffix 6 version parts (-40 < TJ < 106° C). In this case, parts

must be ordered at least with the temperature range suffix 6.

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