SM74104 Datasheet, PDF (12/16 Pages) Texas Instruments – SM74104 High Voltage Half-Bridge Gate Driver with Adaptive Delay

the diode power loss is proportional to frequency. Larger ca-
pacitive loads require more current to recharge the bootstrap
capacitor resulting in more losses. Higher input voltages
(V_IN) to the half bridge result in higher reverse recovery loss-
es. The following plot was generated based on calculations
and lab measurements of the diode recovery time and current
under several operating conditions. This can be useful for ap-
proximating the diode power dissipation.
Diode Power Dissipation V_IN = 80V
Diode Power Dissipation V_IN = 40V
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The total IC power dissipation can be estimated from the
above plots by summing the gate drive losses with the boot-
strap diode losses for the intended application. Because the
diode losses can be significant, an external diode placed in
parallel with the internal bootstrap diode (refer to Figure 2)
can be helpful in removing power from the IC. For this to be
effective, the external diode must be placed close to the IC to
minimize series inductance and have a significantly lower for-
ward voltage drop than the internal diode.
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FIGURE 2. SM74104 Driving MOSFETs Connected in Synchronous Buck Configuration
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