AN2846 datasheet(20/35 Pages) STMICROELECTRONICS

20 / 35 page

Thermal dissipation calculation

AN2846

20/35

Doc ID 15130 Rev 1

2.2

Reverse polarity on a single input case

Each input resistor can be connected to a reverse polarity down to -30 V. This case

corresponds to a connection mistake or a reverse biasing that is generated by the

demagnetization of a monitored inductive solenoid. The involved input can withstand a high

reverse current up to 20 mA. The corresponding state transmitted is low level. The other

inputs remain operational.

The power dissipated into a reverse polarized input is low, but attention has to be paid to

power dissipation into the input resistor which sustains almost all the reverse voltage.

2.3

Temperature gradient on the SCLT3 and on the board

Figure 29 shows the case top temperature when SCLT3-8 dissipates 600 mW, which

corresponds to maximum supply case with VCC and all module inputs at 32 V. The heat sink

is 100 mm2, and the ambient temperature is 25 °C. In this example the maximum case top

temperature reaches 68 °C. The case top temperature is a good indication of the junction

temperature, which can be estimated using thermal analysis techniques.

Figure 29.

Case top temperature

()

2.2

and

for

390

Pdis_RIN

R = 1.1 k

= 2.2 k

Lens: G1

(Board paint in black)

AN2846 Datasheet(PDF) 20 Page - STMicroelectronics