Download Common source inductance introduced self-turn-on in

Common source inductance introduced self-turn-on
in MOSFET turn-off transient
Wen Zhang, Zheyu Zhang, Fred Wang, Daniel Costinett, Leon Tolbert, Benjamin Blalock
The University of Tennessee, Knoxville
INTRODUCTION
• Fast switching semiconductor presents unwanted oscillation
during switching transient.
• While many unwanted oscillations have been reported in
literature, an abnormal continuous ringing is observed when
testing a Si CoolMOS (IXKR47N60C5) in double pulse test.
• Increasing ringing magnitude in drain-source voltage and huge
spikes in gate-source voltage are the key features.
• In the worst case, the ringing is not damped and keeps going
until power supply is killed. In other words, the control of the
switch is lost.
• Adverse effect of common source inductance in fast switching is
revealed and it is recommended to minimize it in circuit and
package design.
Fig. 1. Experimental waveforms showing continuous oscillation during turn-off
transient: 200 V dc bus voltage, 30 A load current and 4.7 Ω gate resistance.
MODELING AND ANALYSIS
Experimental
High 𝑑𝑣/𝑑𝑡 makes 𝐶𝑜𝑠𝑠 take
over all the load current and
MOSFET channel is turned off
Simulation Model
Oscillation in power loop
applies a voltage bias to gate
loop through common source
inductance
Gate source capacitance is
charged beyond 𝑉𝑡ℎ and the
MOSFET channel is turned on
again in turn-off transient
CONCLUSION
• Fast switching worsens the power loop and gate loop parasitics interaction and creates switching failure.
• Traditional TO-247 package with 3 nH common source inductance can render fast switching impossible.
• Circuit and package designers are advised to minimize common source inductance as much as possible and
use Kelvin source connection whenever possible.