2.11 Miller Clamp

IGBT power circuits are commonly connected in a half bridge configuration with the collector of the bottom IGBT tied to the emitter of

the top IGBT.

When the upper IGBT turns on (while the bottom IGBT is in the off state), the voltage on the collector of the bottom IGBT flies up sever-

a positive gate voltage spike and can turn on the bottom IGBT. This behavior is called Miller parasitic turn on and can be destructive to

the switch since it causes shoot through current from the rail right across the two IGBTs to ground. The Si828x Miller clamp’s purpose

VL

VH

Driver Control

2.0 V

CLMP

Driver Control

Soft Shutdown

VSSB

VSSB

VSSB

VDDB

Figure 2.4. Miller Clamp Device

The Miller clamp device (Clamp) is engaged after the main driver had been on (VL) and pulled IGBT gate voltage close to VSSB, such

that one can consider the IGBT being already off. This timing prevents the Miller clamp from interfering with the driver’s operation. The

engaging of the Miller Clamp is done by comparing the IGBT gate voltage with a 2.0 V reference (relative to VSSB) before turning on

the Miller clamp NMOS.

Si8281/82/83/84 Data Sheet

System Overview

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