Thermal management

AN3031

20/28

Doc ID 16144 Rev 1

5

Thermal management

The SCLT3-8BT8 device limits the current that flows in each input pin. Together with a

voltage drop on each input pin versus GND, it also creates power dissipation. Another

contribution is power dissipation coming from the supply voltage pin. The sum of both of

these portions causes an increase in the junction temperature. The maximum allowed

junction temperature of the SCLT3-8BT8 is 150 °C. The HTSSOP38 package with a given

PCB surface has a thermal resistance (junction-to-ambient) of 80 °C / W, as specified in the

device datasheet. This parameter allows the determination of the maximum ambient

temperature during device operation. The ambient temperature to take into account is the

air temperature near the component.

The main equation corresponds to the following:

Equation 6

where:

●

●

●

●

This paragraph presents the method to evaluate the dissipated power.

Figure 16.

Signal conventions / protection structure

The maximum ambient temperature determines the maximum allowed

the maximum power dissipation, refer to the parameter of the datasheet that gives the

maximum specification of the current limitation. The purpose is to add all “thermal supplies”

inside the die. There are 2 main sources of power dissipation: the current limiters embedded

regulator. Then, the maximum power dissipation can be estimated as follows:

Equation 7

As shown in Equation 7 we must subtract the power dissipated by the indicator LEDs and

voltage regulator load.

IN1

COMP

…

SCLT3–8

RI

IC

VC

RC

Input

CI

VIN

…

VI

CC

VC

VCC

COMS

VDD

VDD

IDD

LD1

Supply

voltage

IIN

Load

VF

IIN

AM00620