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
LM5104
www.ti.com
SNVS269C –JANUARY 2004–REVISED MARCH 2013
POWER DISSIPATION CONSIDERATIONS
The total IC power dissipation is the sum of the gate driver losses and the bootstrap diode losses. The gate
driver losses are related to the switching frequency (f), output load capacitance on LO and HO (C
L
), and supply
voltage (V
DD
) and can be roughly calculated as:
P
DGATES
= 2 • f • C
L
• V
DD
2
(1)
There are some additional losses in the gate drivers due to the internal CMOS stages used to buffer the LO and
HO outputs. The following plot shows the measured gate driver power dissipation versus frequency and load
capacitance. At higher frequencies and load capacitance values, the power dissipation is dominated by the
power losses driving the output loads and agrees well with the above equation. This plot can be used to
approximate the power losses due to the gate drivers.
Figure 19. 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 20. Diode Power Dissipation V
IN
= 80V Figure 21. Diode Power Dissipation V
IN
= 40V
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