Datasheet

10.0 kHz 100.0 kHz 1000.0 kHz
SWITCHING FREQUENCY (kHz)
0.001
0.010
0.100
1.000
POWER (W)
1.0 kHz
C
L
= 0 pF
C
L
= 4400 pF
10.0 kHz 100.0 kHz 1000.0 kHz
SWITCHING FREQUENCY (kHz)
0.001
0.010
0.100
1.000
POWER (W)
1.0 kHz
C
L
= 0 pF
C
L
= 4400 pF
0.1 1.0 10.0 100.0 1000.0
SWITCHING FREQUENCY (kHz)
POWER (W)
0.001
0.010
0.100
1.000
C
L
= 4400 pF
C
L
= 2200 pF
C
L
= 0 pF
C
L
= 470 pF
C
L
= 1000 pF
LM5105
www.ti.com SNVS349C –FEBRUARY 2005–REVISED MARCH 2013
Figure 21. Gate Driver Power Dissipation (LO + HO)
V
CC
= 12V, Neglecting Diode Losses
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
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 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.
Figure 22. Diode Power Dissipation V
IN
= 80V Figure 23. Diode Power Dissipation V
IN
= 40V
The total IC power dissipation can be estimated from the above 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 with the internal bootstrap diode (refer to Figure 24) and 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 © 2005–2013, Texas Instruments Incorporated Submit Documentation Feedback 11
Product Folder Links: LM5105