Due to the strong drive strength of the UCC21750,
careful considerations must be taken in PCB
design. Below are some key points:
- The driver must be placed as close as possible to the power semiconductor to
reduce the parasitic inductance of the gate loop on the PCB traces.
- The decoupling capacitors of the input and output power supplies must be placed
as close as possible to the power supply pins. The peak current generated at
each switching transient can cause high dI/dt and voltage spike on the parasitic
inductance of PCB traces.
- The driver COM pin must be connected to the Kelvin connection of SiC MOSFET source or IGBT emitter. If the power device does not have a split Kelvin source or emitter, the COM pin must be connected as close as possible to the source or emitter terminal of the power device package to separate the gate loop from the high power switching loop
- Use a ground plane on the input side to shield the input signals. The input
signals can be distorted by the high frequency noise generated by the output
side switching transients. The ground plane provides a low-inductance filter for
the return current flow.
- If the gate driver is used for the low side switch which the COM pin connected to the dc bus negative, use the ground plane on the output side to shield the output signals from the noise generated by the switch node; if the gate driver is used for the high side switch, which the COM pin is connected to the switch node, ground plane is not recommended
- If ground plane is not used on the output side, separate the return path of the
DESAT and AIN ground loop from the gate loop ground which has large peak source
and sink current.
- No PCB trace or copper is allowed under the gate driver. TI recommends a PCB
cutout to avoid any noise coupling between the input and output side which can
contaminate the isolation barrier.