10.0

100.0

1000.0

SWITCHING FREQUENCY (kHz)

0.001

0.010

0.100

1.000

1.0

10.0

100.0

1000.0

SWITCHING FREQUENCY (kHz)

0.001

0.010

0.100

1.000

1.0

NRND

LM5100, LM5101

www.ti.com

SNVS267C – MAY 2004 – REVISED MARCH 2005

The bootstrap diode power loss is the sum of the forward bias power loss that occurs while charging the

bootstrap capacitor and the reverse bias power loss that occurs during reverse recovery. Since each of these

events happens once per cycle, the diode power loss is proportional to frequency. Larger capacitive loads

the half bridge result in higher reverse recovery losses. 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 approximating the diode power dissipation.

The total IC power dissipation can be estimated from the previous plots by summing the gate drive losses with

the bootstrap diode losses for the intended application. Because the diode losses can be significant, an external

diode placed in parallel (refer to Figure 19) with the internal bootstrap diode 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 forward voltage drop than the internal diode.

Copyright © 2004–2005, Texas Instruments Incorporated

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