LO1

PGND

LM5112

LM5112

VCC

BST1

HO1

HS1

VIN

LM5045

LO1

PGND

VCC

BST1

HO1

HS1

VIN

LM5045

Q1

Q2

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.

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.

Figure 33. Using a Low Side Gate Driver to Augment Gate Drive Strength

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