9020 Datasheet, PDF (19/25 Pages) Fairchild Semiconductor – IGBT Basic II

Vdc
L
O
A
D
Vsense
5. RBSOA
Fig. 8. Short-circuit sensing circuit using de-saturation method
40
10
1
1
Safe Operating Area
V_GE = 20V, T_C = 100℃
10
100
Collector-Emitter Voltage, V_CE [V]
Fig. 9. Typical RBSOA of IGBT
1000
During turn-off transient, the gate bias with a positive value is switched to zero or to a negative
value, which leaves the device with high voltage and hole current. Safe operating area for
such operations is called RBSOA (refer to Fig. 9). Unlike FBSOA, snubber circuit design is
important for safe operation during IGBT turn-off. Wider RBSOA can be obtained by reducing
PNP transistor’s current gain. If RBSOAs of p-channel and n-channel IGBT with identical dop-
ing profile and cell structure are compared, n-channel has larger SOA for the collector voltage
(avalanche induced SOA limit), but the SOA for the collector current (current induced latch-up
limit) is smaller. p-channel, on the other hand, is the opposite of n-channel. The limit of the
avalanche induced SOA is affected by the impact ionization coefficient for the carrier of the
depletion layer. Impact ionization coefficient of the holes transported from the n-channel IGBT
is lower than that of electrons, which allows n-channel IGBT to have excellent avalanche
induced SOA limits. In addition, N base region sheet resistance of the p-channel IGBT is about
2.5 times lower than the P base region sheet resistance of the n-channel IGBT, so p-channel
IGBT is superior to the n-channel IGBT in current induced latch-up limit.
19
Rev. A, April 2002