AN3031 Datasheet, PDF (21/28 Pages) STMicroelectronics – SCLT3-8 input termination demonstration board

AN3031
Thermal management
Considering the above application structure and the following conditions:
● V_CC = 30 V
● V_{I_MAX} = 30 V
● I_{IN_MAX} = 2.7 mA
● V_{IN_MAX} = 24 V
● f_CLK = 1.3 MHz
● I_C = 6 mA
● V_C = 24 V
● V_F = 1.9 V
● V_DD = 5 V
● I_D = 4.5 mA
● R_C = 1 kΩ
● R_I = 2.2 kΩ
the overall chip power dissipation is:
Equation 8
P_D = 8 x [(V_IN – V_F) x I_IN] + V_C x I_C – V_DD x I_DD = 8 x [(24V – 1.9V) x 2.7mA] + 24V x 6mA – 5V x 4.5 A = 599mW
In case of a maximum allowed ambient temperature equal to 100 °C, the thermal resistance
must be lower than:
Equation 9
R_THJAMAX
=
Δ_----T_{----J----–---A--}
P_D
=
1_----5_---0_----°_---C_{------–-----}1_---0_----0_---°_----C_---
0.599W
=
83° C ⁄
W
Since the application R_TH value of the HTSSOP38 is 80 °C/W, the SCLT3-8BT8 works
correctly at this ambient temperature.
In the final application we must consider other cases also. One example is spurious
connection of one channel to negative voltage.
In this negative biasing of the input, the current (I_REV) flows through the protection diode.
The voltage (V_REV) is then equal to the forward voltage of the protection diode, which is
approximately 0.7 V at 16 mA.
All of the other inputs work correctly.
The total power dissipation in this case can be calculated by with the equation:
Equation 10
I_REV
=
V_{-----C---C-----–-----}V_{----R----E---V--}
R_IN
=
3_----02_{----2-–--0--}0_-0--._--Ω7_----V_{-- =}
13mA
Doc ID 16144 Rev 1
21/28