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The SiC MOSFET half-bridge gate driver evaluation board

Broadcom Inc

The Goal

In order to enable an easier transition toward SiC technology, Broadcom® is expanding its Isolated Gate Driver portfolio, accompanied with the appropriate evaluation boards for 1200V SiC MOSFETs. The first board coming from this series is the Isolated Gate Driver evaluation board made for the industry's most popular baseplate-less module in Easy1B® package.

The Challenge

SiC MOSFET has typically 5-10 times faster transients than IGBT. A lot of effort is required for the PCB board layout in order to minimize parasitics and EMI. Fast transients require high common-mode transient immunity on the board level and as well as on the isolating IC level. Additionally, due to the smaller physical size of the SiC MOSFET chip, SiC MOSFETs have no or only limited short circuit robustness. In the case of the short circuit, drain current is reaching very high values in a much shorter period of time, when compared to traditional Si IGBTs. For this reason, a very fast short current detection, within 1-2 µs period, is required. We presented a simple solution to minimize the detection time and provide protection in case of a destructive short circuit event.

The Solution

Evaluation board EB1200-355JC features Broadcom’s dual output isolated gate drive optocouplers ACPL-355JC, used to drive SiC MOSFET module in Easy1B® housing, precision optically isolated amplifiers ACPL-C87B used for DC Bus voltage and temperature measurements, and optically isolated sigma-delta modulator ACPL-736J used for output current measurement. In addition, the board features an integrated capacitor DC Bus with an optimized layout that minimizes the commutation loop inductance. EB1200-355JC is developed to support Broadcom customers during their first steps in designing power converter applications with ACPL-355JC drivers.EB1200-355JC is originally designed to be used with Easy1B SiC MOSFET module FF11MR12W1M1. With adequate adjustments regarding overcurrent (OC) protection and gate resistors, the EB1200-355JC can support modules from different manufacturers in the same packaging, rated up to 1200V, and having the same pin assignment event.

 

  • Two isolated ACPL-355JC gate drive optocouplers with following features: 
  •     Overcurrent protection (or DESAT)
  •     UVLO (under-voltage lockout) protection
  •     Dual output drive to control turning on and off transients 
  •     Soft shutdown during fault
  •     Two isolated feedback signals, FAULT (for overcurrent) and UVLO
  •     100 kV/µs common-mode transient immunity
  •     2262V IEC Maximum Working Insulation Voltage Viorm (VPEAK)
  •     5000V UL Insulation Rating Viso (VRMS)
  • Two ACPL-C87B optically isolated amplifiers for DC Bus voltage and temperature measurement:
  •     0 to 2 V nominal input range
  •     100 kHz bandwidth
  •     3 V to 5.5 V wide supply range for the output side
  •     15 kV/µs common-mode transient immunity
  • ACPL-736J optically isolated sigma-delta modulator for output current measurement:
  •     ±50mV linear range
  •     20MHz external CLK
  •     CMOS clock and data interface
  •     1-bit, second-order sigma-delta modulator
  • Electrically and mechanically suitable for easy 1B module FF11MR12W1M1
  • With adjustment of the OC protection and gate resistors, the evaluation board supports the following easy 1B SiC MOSFET modules:
  •     FF23MR12W1M1
  •     CAB016M12FM3
  • DC Bus and balancing/discharge resistors
  • DC/DC power supply with current limit protection and thermal shutdown
  • Isolated SMPS for gate drivers
  • Access to FAULT and UVLO output signals for protection and control development purposes.
  • Access to PWM input signals
  • Access to measurement signals (voltage and current)