1EDS5663H Ver la hoja de datos (PDF) - Infineon Technologies

Número de pieza

componentes Descripción

Fabricante

1EDS5663H

GaN EiceDRIVER™ product family

Infineon Technologies 

1EDF5673K, 1EDF5673F, 1EDS5663H

GaN gate driver

Background and system description

2

Background and system description

Although gallium nitride high electron mobility transistors (GaN HEMTs) with ohmic pGaN gate like Infineon’s

600 V CoolGaN™ power switches are robust enhancement-mode ("normally-on") devices, they differ significantly

from MOSFETs. The gate module is not isolated from the channel, but behaves like a diode with a forward voltage

VF of 3 to 4 V. Equivalent circuit and typical gate input characteristic are given in Figure 2. In the steady "on" state

a continuous gate current is required to achieve stable operating conditions. The switch is "normally-off", but the

threshold voltage Vth is rather low (~ +1 V). This is why in certain applications a negative gate voltage -VN, typically

in the range of several volts, is required to safely keep the switch "off" (Figure 2b).

Figure 2 Equivalent circuit (a) and gate input characteristics (b) of typical normally-off GaN HEMT

Obviously the transistor in Figure 2 cannot be driven like a conventional MOSFET due to the need for a steady-

state "on" current Iss and a negative "off" voltage -VN. While an Iss of a few mA is sufficient, fast switching transients

require gate charging currents Ion and Ioff in the 1 A range. To avoid a dedicated driver with 2 separate "on" paths

and bipolar supply voltage, the solution depicted in Figure 3 is usually chosen, combining a standard gate driver

with a passive RC circuit to achieve the intended behavior. The high-current paths containing the small gate

resistors Ron and Roff, respectively, are connected to the gate via a coupling capacitance CC. CC is chosen to have

no significant effect on the dynamic gate currents Ion and Ioff. In parallel to the high-current charging path the

much larger resistor Rss forms a direct gate connection to continuously deliver the small steady-state gate

current, Iss. In addition, CC can be used to generate a negative gate voltage. Obviously, in the "on"-state CC is

charged to the difference of driver supply VDDO and diode voltage VF. When switching to the "off" state, this charge

is redistributed between CC and CGS and causes an initial negative VGS of value

(2.1)

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with QGeq denoting an equivalent application-specific gate charge, i.e. QGeq ~ QGS for hard-switching and QGeq ~ QGS

+ QGD for soft-switching transitions. VN can thus be controlled by proper choice of VDDO and CC. During the "off"

state the negative VGS decreases, as CC is discharged via Rss. The associated time constant cannot be chosen

independently, but is related to the steady-state current and is typically in the 1 µs range. The negative gate

voltage at the end of the "off" phase (VNf in Figure 3b) thus depends on the "off" duration. It lowers the effective

driver voltage for the following switching "on" event, resulting in a dependence of switching dynamics on

frequency and duty cycle as one drawback of this approach.

Final datasheet

6

Rev. 2.3

2020-10-22

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