Broadcom Ltd.

- 1 -

Introduction

SiC devices including SiC MOSFET and SiC Schottky diodes are

recognized as next generation wide bandgap devices. They

can provide fast switching with less loss compared to

conventional Si devices and improve overall system efficiency.

The higher switching capability and frequency can reduce the

overall system size and costs. The technical benefits coupled

with lower costs have increased the fast adoption of SiC power

semiconductors in applications like industrial motor control,

induction heating and industrial power supplies and

renewable energy.

Broadcom gate drive optocouplers are used extensively with

Silicon-based semiconductors IGBT and Power MOSFETs can

also be used for SiC operations. Optocouplers are used to

provide reinforced galvanic insulation between the control

circuits from the high voltages and the power semiconductors.

The ability to reject high common mode noise (CMR) will

prevent erroneous driving of the SiC power semiconductors

during high frequency switching.

Figure 1 KIT8020CRD8FF1217P-1 SiC MOSFET Evaluation Kit

This evaluation kit, KIT8020CRD8FF1217P-1 is meant to

demonstrate the high performance of Wolfspeed (CREE) 1200V

SiC MOSFET (C2M0080120D) and SiC Schottky diodes

(C4D20120D) in the standard TO-247 package. The kit also

includes Broadcom gate drive optocouplers ACPL-W346,

power supplies and all the other components needed to

quickly assemble the half bridge power stage. The basic block

diagram and specifications are shown in Figure 2. The

assembly can be easily configured for several topologies from

the basic phase-leg configuration to several other common

topologies. Additional topologies like H-bridge and 3-phase

inverter are possible with two or more of the evaluation kits.

ACPL-W346

Wolfspeed (CREE) SiC MOSFET C2M0080120D

Evaluation Kit

Broadcom Ltd.

- 2 -

ACPL-W346

Evaluation Kit

Evaluation Kit Overview

Figure 2 KIT8020CRD8FF1217P-1 Basic Block Diagram

This reference design will describe the basic operation of using

gate drive optcoupler ACPL-W346 for the SiC MOSFET

evaluation kit. Purchase of the evaluation kit and the user's

manual are available from catalogue distributors:

http://www.digikey.sg/product-detail/en/KIT8020-CRD-8FF121

7P-1/KIT8020-CRD-8FF1217P-1-ND/5027643

http://www.mouser.sg/ProductDetail/Cree-Inc/KIT8020-CRD-8

FF1217P-1/?qs=%2fha2pyFadugoWU85a9ES3mGSyQOWKTBm

odw8qlZLPgNqDts0nlnPYD4v%252bh%2fKfVJR

Evaluation Kit Overview

Figure 3 Block Diagram with Gate Drive Optocoupler ACPL-W346

The evaluation kit uses 2 gate drive optocoupler ACPL-W346 to

drive the SiC MOSFET directly in the half bridge topology. The

ACPL-W346 is a basic gate driver optocoupler used to isolate

and drive the SiC MOSFET operating at high DC bus voltage. It

has a rail-to-rail output with 2.5A maximum output current to

provide fast switching high voltage and high driving current to

turn-on and off the SiC MOSFET efficiently and reliably. The

unique feature of ACPL-W346, is the speed and is the industry's

fastest in its class. The maximum propagation delay is 120ns

and typical rise and fall times are around 10ns. The very high

CMR, common mode rejection of 50kV/μs is required to isolate

high transient noise during the high frequency operation from

causing erroneous outputs. It can provide isolation certified by

UL1577 for up to VISO 5000VRMS/min and IEC 60747-5-5 for

working voltage, VIORM up to 1140VPEAK.

The 2W DC/DC converter with +12V VCC input generates +24V

Vcc_out output voltage with 6kVDC isolation that is supplying

voltage to ACPL-W346 on push-pull gate drive of the

secondary side as shown in Figure 3. In this circuit, a 5V zener in

parallel with 1uF capacitor is used to generate -5V Vgs voltage

for the SiC MOSFET turn-off and turn-on Vgs voltage is equal to

24V-5V=19V. Note that SiC MOSFET can be turned off with zero

voltage, and the -5V turn-off voltage helps with faster turn-off

and lower turn-off losses and also improves dv/dt induced

self-turn-on and noise immunity during transient periods with

more margin for Vgs turn-on threshold voltage.

Hardware Description and Board Design

Figure 4 Evaluation Kit Key Connectors and Components

In a synchronous phase-leg Buck converter topology, CON1

connects to the positive DC BUS rail, CON2/5 connects to the

negative BUS rail or GND and CON3 the output of the

converter. Several topologies can be configured with this

board: synchronous Buck, non-synchronous Buck (or high-side

Buck), synchronous Boost, non-synchronous Boost, half

phase-leg bridge converter, H bridge converter (2x EVL boards)

and bi-directional buck-boost converters. Please refer to the