UCC5350-Q1: pros and cons of the MC and SB version

Hi Zehui,

The split output version lets you to use a different turn-off resistor and turn-on resistor without needing an extra diode and its associated diode drop. This can be used to fine-tune the efficiency vs. overshoot of the FET switching. However, any Miller injection current will have to drain into the turn-off resistance. A turn-off resistor >0 will directly increase the Vgs Miller spike voltage.

The Miller clamp pin will provide 0 ohms of impedance to the Miller injection current, resulting in the lowest possible Vgs Miller spike. It is an additional FET in parallel to the main pull-down NMOS, so it provides lower Miller impedance and stronger turn-off when combined with a 0 ohm turn-off.

I usually recommend optimizing the HV bus to eliminate switch node ringing, not increasing Rg and switching losses. Therefore, I recommend the Miller clamp version, with a minimal Rg (1-5 ohms). The UCC5350 already has an asymmetric internal Roh (12 ohms) and Rol (0.5 ohms), and this is sufficient to limit ringing in a well dampened and decoupled half bridge. It may just require adding more high-voltage decoupling and snubbing.

Best regards,

Sean 

Hi Zehui,

If you are using a SiC FET or IGBT, which are are more suitable for a Higher BUS voltage, the split output will probably be sufficient. If you use Si FETs, you will likely require the Miller Clamp.

Best regards,

Sean