SI8233 Datasheet, PDF (24/57 Pages) Silicon Laboratories – 0.5 AND 4.0 AMP ISODRIVERS

Si823x
T_j = P_d  _ja + T_A
= (0.145)(105) + 20
= 35.2 °C
The maximum power dissipation allowable for the Si823x is a function of the package thermal resistance, ambient
temperature, and maximum allowable junction temperature, as shown in Equation 2:
P_Dmax

-^T---^j--^m----^a---^x----–----^T----^A--
ja
where:
P_Dmax = Maximum Si823x power dissipation (W)
T_jmax = Si823x maximum junction temperature (150 °C)
T_A = Ambient temperature (°C)
ja = Si823x junction-to-air thermal resistance (105 °C/W)
f = Si823x switching frequency (Hz)
Equation 2.
Substituting values for P_Dmax T_jmax, T_A, and _ja into Equation 2 results in a maximum allowable total power
dissipation of 1.19 W. Maximum allowable load is found by substituting this limit and the appropriate data sheet
values from Table 1 on page 6 into Equation 1 and simplifying. The result is Equation 3 (0.5 A driver) and
Equation 4 (4.0 A driver), both of which assume VDDI = 5 V and VDDA = VDDB = 18 V.
C_L(MAX)
=
1_----._--4_----_-----1_---0_----^–_---³_{- – 7.5  10}–11
f
Equation 3.
C_L(MAX)
=
1_----._--4_----_-----1_---0_----^–_---³_{- – 3.7  10}–10
f
Equation 4.
Equation 3 and Equation 4 are graphed in Figure 35 where the points along the load line represent the package
dissipation-limited value of CL for the corresponding switching frequency.
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Rev. 1.7