USER GUIDE
UG499: Si828x-AW-GDB Gate Driver Boards
Skyworks Solutions, Inc. • Phone [949] 231-3000 • [email protected] • www.skyworksinc.com
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November 10, 2022
7. User Configuration Options
7.1. Series Gate Resistors
The Si828x GDB has 1
Ω
series gate resistors in series with the gate drive signal for both the high side and the low side chan-
nels. In addition, these resistor values are the same for both turn on (RG-ON) and turn off (RG-OFF).
However, the user can select any value for turn-on and turn off timing control independently. Resistors R348 and R350 con-
trol the turn-on timing for the high side and low side channels respectively. Resistors R349 and R51 affect the turn-off time
for the high side and low side respectively. This configuration provides the user with complete flexibility in tuning the turn-on
and turn-off times for each channel.
7.2. Negative Gate Bias
The default configuration of this driver board provides a gate drive signal that swings from +15 V to -3.7 V with respect to the
source pin connection.
7.3. Isolated Driver Power Supply Voltage
The Si828x GDB uses a dc-dc converter integrated into the Si8284 gate driver. This converter regulates the output of one sec-
ondary of the transformer used in the application. The design of the transformer provides regulation of the other secondary
winding to provide separate, isolated power supplies for both the high side and low side driver. The default configuration pro-
vides a driver power supply that is regulated to 19 V. Since the source pin of each channel is biased about 3.6 V above the
converter's reference, the gate will see a voltage swing from +15 V to -4 V when measured with respect to the source pin.
The DC-DC converter may be operated with a different set of output voltages by changing the resistor divider (R1/R2+1) *
1.05V to obtain the desired supply voltage. The limit of VDDB - VSSB is 30V, and the VDDB/VSSB ratio is fixed by the turns
ratios of transformer T1. Operating the device at a higher voltage may impair operation or damage the device.
7.4. Overcurrent/Desaturation Trip Level
The overcurrent (OC) fault detection circuit measures the on-state VDS voltage across each switch position and triggers a
fault condition if the voltage rises above a set level. The internal comparator trip voltage in the Si828x gate driver IC is 7 V.
Considering the forward voltage of the high-voltage blocking diodes and a tunable Zener diode, the overcurrent trip level is
calculated with the following equation:
VOC-Trip = 7V - VZ - 2VF
where the forward voltage of the high-voltage diodes, VF, is approximately 0.5 V, and the Zener voltage, VZ, included on the
gate driver is 3.9 V (On Semi MMSZ4686T1G). As shipped, the Zener diode is replaced with a 0 Ohm resistor and the overcur-
rent trip level is 6 V. If it is desired to change the overcurrent trip level, the Zener diode should be in a SOD123 package such
as the diodes in the MMSZ series from On Semi. The Zener diodes are labeled D323 and D324 on the PCB.
