SM72295_15 Datasheet, PDF (9/17 Pages) Texas Instruments – SM72295 Photovoltaic Full Bridge Driver

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Timing Diagram
SM72295
SNVS688E – OCTOBER 2010 – REVISED APRIL 2013
LI
HI
LO
HO
t_MON
t_MOFF
LI
HI
t_HPLH
t_LPLH
t_HPHL
t_LPHL
LO
HO
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_DD2
(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 13. Gate Driver Power Dissipation (LO + HO)
V_CC = 12V, Neglecting Diode Losses
1.000
C_L = 4400 pF
0.100
C_L = 1000 pF
0.010
C_L = 0 pF
0.001
0.1
1.0
10.0
100.0
SWITCHING FREQUENCY (kHz)
1000.0
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. 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.
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