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componentes Descripción

Fabricante

1EDS5663H

GaN EiceDRIVER™ product family

Infineon Technologies 

1EDF5673K, 1EDF5673F, 1EDS5663H

GaN gate driver

Background and system description

Gate drive

GaN switch

D

Rss Iss

VGS

S1

+

VDDO

Ion

G

Ron

Ioff

CC

Roff

S2

a)

CGD

CGS

CDS

S

VDDO

VF

0

-VN

on

off

t

-VNf

b)

Figure 3 Equivalent circuit of GaN switch with RC gate drive (a) and gate-to-source voltage VGS (b)

A second problem might happen if two switches are used alternately in a half-bridge configuration. In normal

operation always one of the switches is "on", and before switching on the other one, it has to be switched off,

thereby generating the negative gate voltage VN. The usually short period with both switches "off" (dead time td)

does not cause a significant increase of VGS. If, however, there is by any reason a longer period with both switches

in "off" state (e.g. during system start-up, burst mode operation etc.), both coupling capacitors (CC) will be

discharged. Thus, for the first switching pulse after such an extended non-switching period no negative voltage

is available. This could lead to increased transistor stress or even instabilities due to spurious turn-on effects in

half-bridge topologies.

To solve the problems described above, a shape of VGS like the one in Figure 4b) would be required rather than

the one in Figure 4a) which results from the simple RC circuit. As explained, a negative VGS might be needed for

safe "off" states during the switching transients, but it should be as low as possible. Due to the lack of a physical

body diode any negative VGS adds to the voltage drop of a GaN transistor in reverse polarity (diode operation)

thereby increasing the conduction losses during dead time. Thus in the idealized waveform of Figure 4b) VGS is

switched to the minimum required VN for a constant time t1 longer than the system dead time td. After that VGS is

switched back to zero to ensure identical conditions for the next switch "on" event and to minimize losses from

diode operation. If, however, an "off" state lasts for a time t2 significantly longer than a normal switching period

1/fsw (e.g. several µs), VGS should be switched again to -VN to avoid the described "first pulse" problem.

PWM

t2 >> 1/fsw

VGS

a)

-VN

VGS

t1 > td

b)

-VN

Figure 4

VGS

c)

-VN

-VDDO

VGS voltage waveforms with RC circuit (a), improved (b) and proposed shape (c)

Final datasheet

7

Rev. 2.3

2020-10-22

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