SI8261AAC-C-IS Datasheet, PDF (19/40 Pages) Silicon Laboratories – 5 KV LED EMULATOR INPUT, 4.0 A ISOLATED GATE DRIVERS

Si826x
5.4. Power Dissipation Considerations
Proper system design must assure that the Si826x operates within safe thermal limits across the entire load range.
The Si826x total power dissipation is the sum of the power dissipated by bias supply current, internal switching
losses, and power delivered to the load, as shown in Equation 1.
P_D = I_F  V_F  DC + V_DD  I_DDQ + Q_d + C_L  V_DD  f
where: P_D is the total device power dissipation (W)
I_F is the diode current (30 mA max)
V_F is the diode anode to cathode voltage (2.8 V max)
DC is duty cycle (0.5 typical)
V_DD is the driver-side supply voltage (30 V max)
I_DDQ is the driver maximum bias current (2.5 mA)
Q_d is 3 nC
C_L is the load capacitance
f is the switching frequency (Hz)
Equation 1.
The maximum allowable power dissipation for the Si826x 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 is the maximum allowable power dissipation (W)
T_jmax is the maximum junction temperature (140 °C)
T_A is the ambient temperature (°C)
_ja is the package junction-to-air thermal resistance (110 °C/W)
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 1.0 W. Note that the maximum allowable load is found by substituting this limit and the appropriate
datasheet values from Table 2 on page 4 into Equation 1 and simplifying. Graphs are shown in Figures 17 and 18.
All points along the load lines in these graphs represent the package dissipation-limited value of C_L for the
corresponding switching frequency.
Rev. 1.3
19