AN2738 datasheet(37/54 Pages) STMICROELECTRONICS

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AN2738

How to increase the gate driver output current capability

Doc ID 14589 Rev 2

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How to increase the gate driver output current

capability

In some cases, certain applications may require more gate driver output current capability.

This requirement could be found in systems having a power rating higher than about 1 kW.

In those applications, in fact, typically the power MOSFET/IGBTs have a large gate charge

which contributes to a slowing down of the power switch transition (the dVOUT/dt), increasing

the power dissipation during each commutation. Note that also in applications with power

rating higher than 1 kW, the output current capability of the L6390 could be enough if the

power dissipation for commutation is acceptable (the power dissipation due to RDS(on) or

VCESAT is not dependent on the gate current). But if the limitation of this power contribution

is a constraint, the dVOUT/dt of each transition must be increased by enhancing the current

capability of the gate driver.

A simple way to increase the current capability of the gate driver outputs is to insert, in

series with the two gate lines of one half-bridge gate driver IC, two external current buffers

(Figure 33).

Figure 33.

Block diagram of output current capability enhancement using external

current buffers

Typically the current buffers are implemented using bipolar NPN-PNP push-pull non-

inverting (emitter follower configuration) structures. In Figure 34, a typical circuit using a

gate driver with bipolar push-pull current buffers is shown.

HVG

H.V.

TO LOAD

OUT

LVG

BOOT

GND

VCC

GATE

DRIVER

CURRENT

BUFFERS

AN2738 Datasheet(PDF) 37 Page - STMicroelectronics