Datasheet

10.0 100.0 1000.0
SWITCHING FREQUENCY (kHz)
0.001
0.010
0.100
1.000
POWER
(
W)
1.0
C
L
= 0 pF
C
L
= 4400 pF
10.0 100.0 1000.0
SWITCHING FREQUENCY (kHz)
0.001
0.010
0.100
1.000
POWER (
W)
1.0
C
L
= 0 pF
C
L
= 4400 pF
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
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 17. Diode Power Dissipation V
IN
= 80V
Figure 18. Diode Power Dissipation V
IN
= 40V
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 Submit Documentation Feedback 11
Product Folder Links: LM5100 LM5101