LM5045SQ Datasheet, PDF (29/38 Pages) Texas Instruments – Full-Bridge PWM Controller with Integrated MOSFET Drivers

LM5045
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SNVS699G – FEBRUARY 2011 – REVISED MARCH 2013
Depending on the gate charge characteristics of the primary FET, if it is required to speed up both the turn-on
and the turn-off time, a bipolar totem pole structure as shown in Figure 32 can be used. When LO1 goes high,
the gate to source current is sourced through the NPN transistor Q1 and similar to the circuit shown in Figure 31
when LO1 goes low, the PNP transistor Q2 expedites the turn-off process.
LM5045
VIN
BST1
Q1
HO1
Q2
HS1
VCC
LO1
PGND
Figure 32. Bipolar Totem Pole Arrangement
Alternatively, a low side gate driver such as LM5112 can be utilized instead of the discrete totem pole. The
LM5112 comes in a small package with a 3A source and a 7A sink capability. While driving the high-side FET,
the HS1 acts as a local ground and the boot capacitor between the BST and HS pins acts as VCC.
LM5045
VIN
BST1
HO1
LM5112
HS1
VCC
LO1
LM5112
PGND
Figure 33. Using a Low Side Gate Driver to Augment Gate Drive Strength
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