ISL73847SEHDEMO2Z datasheet(28/40 Pages) RENESAS

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R34DS0017EU0104 Rev.1.04

Page 28

Jan 31, 2025

ISL73041SEH Datasheet

6.10 Bootstrap Voltage Overcharge Protection

Traditional MOSFET applications drive the gate-source voltage anywhere from 10V-15V while retaining both 1)

Low drain-source ON-resistance and 2) reliable operation. GaN FET operation has a much narrower range,

usually around 4.5V to 6V, to maintain low ON-resistance and reliable operation.

The ISL73041SEH provides an integrated PVCC LDO to provide bias to the low-side gate driver. The

ISL73041SEH also features unique circuitry to prevent overcharging the boot voltage in the bootstrap

configuration.

Unlike a MOSFET, there is no body-drain diode in a GaN FET. However, there is still a reverse conduction path

from source to drain with zero gate bias. The source-drain voltage is a function of the reverse current and is

provided in the GaN FET datasheet as the VSD parameter. During dead time, when both high and low-side GaN

FETs are off, the positive current flowing through the inductor is commutated through the low-side FET

source-drain channel. The reverse VSD voltage pulls the PHS node of the ISL73041SEH driver below ground. In

traditional half-bridge drivers with a boot diode implementation, the boot diode is forward-biased, and the

bootstrap capacitor is charged to PVCC + VSD. Depending on the magnitude, this can over-charge the bootstrap

capacitor voltage, which provides the upper gate drive voltage.

Important: Operating the GaN FET with higher than recommended gate voltages is unreliable as this can damage

the GaN FET. The recommended operating gate voltage for Renesas GaN FETs is 4.5V.

The ISL73041SEH implements bootstrap capacitor overcharge protection by replacing an external boot diode with

an internal intelligent boot switch. The boot switch turns on only when PWM = 0V and the PHS voltage is within

±250mV of PGND. This avoids recharging the bootstrap capacitor during dead time, where the PHS voltage can

be excessively negative such that it overcharges the bootstrap capacitor. Figure 49 and Figure 50 highlight the

bootstrap overcharge protection by replacing the boot diode with a boot switch.

Figure 49. BOOT Switch Only

Figure 50. Schottky BOOT Diode Added

UGL

PHS

LGH

LGL

Vsd

CBOOT

PVCC

External

Boot Diode

Switch

Control

PWM

PHS

PVIN

BOOT-PHS Voltage

Buck Load Current

0A to 15A Transition

BOOT-PHS Voltage

Buck Load Current

0A to 10A Transition

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