AN2123 STMicroelectronics, AN2123 Datasheet - Page 9

• Manufacturer Part Number: AN2123
• Description: TD351 Advanced IGBT Driver Principles of operation and application
• Manufacturer: STMicroelectronics

AN2123
2-Level turn-off
Figure 13. Waveforms of the 2-level turn-off function (COFF timing exaggerated for illustration)
Practical tests were made with 1200 V - 50 A IGBT modules Fuji 6MBI50S120L. The results shown in
Figure 14
point out how the 2-level turn-off feature can consistently reduce voltage stress on the IGBT in
the event of over-current.
During this test, the 50 A-rated IGBT module has to turn-off a 300 A current simulating an application
faulty condition.
The left-hand graph in
Figure 14
shows a standard commutation. The driver OUT pin voltage is abruptly
pulled from 16 V to 0 V and the IGBT gate is discharged through the gate resistor. The fast turn-off of the
IGBT generates a voltage spike on Vce reaching 1 kV, which is dangerously close to the IGBT absolute
maximum rating (1200 V). The calculated turn-off energy reaches 19 mJ.
The right-hand graph in
Figure 14
shows how the TD351 and its 2-level turn-off feature can help deal with
this situation. During the first phase, the TD351 OUT pin is pulled from 16 V to 9 V during 2.5 µs. In the
second phase the OUT pin is pulled to 0 V. As a consequence, the IGBT turn-off is slightly longer and the
Vce voltage spike is advantageously reduced to 683 V. The calculated turn-off energy reaches 31 mJ,
but the resulting overheating can be more easily managed than the destruction of the IGBT by over-
voltage stress.
Figure 14. Reduction of IGBT over-voltage stress using 2-level turn-off feature
IGBT Vge
IGBT Vge
overshoot 1kV
TD351 OUT
TD351 OUT
overshoot 683V
Vce=400V
Vce=400V
Ic=300A
Ic=300A
2-level turn-off w ith LVoff=9V
standard commutation
9/15