IL33153 Datasheet, PDF (11/14 Pages) Integral Corp. – SINGLE IGBT GATE DRIVER

IL33153
sitic wiring inductance. The fault signal from the De-
saturation Comparator must be blanked sufficiently to
allow the diode to be cleared and the ringing to settle
out. The blanking function uses an NPN transistor to
clamp the comparator input when the gate input is low.
When the input is switched high, the clamp transistor
will turn “off”, allowing the internal current source to
charge the blanking capacitor. The time required for the
blanking capacitor to charge up from the on−voltage of
the internal NPN transistor to the trip voltage of the
comparator is the blanking time.
If a short circuit occurs after the IGBT is turned on
and saturated, the delay time will be the time required
for the current source to charge up the blanking capaci-
tor from the VCE(sat) level of the IGBT to the trip volt-
age of the comparator. Fault blanking can be disabled by
leaving Pin 8 unconnected.
Sense IGBT Protection
Another approach to protecting the IGBTs is to
sense the emitter current using a current shunt or Sense
IGBTs. This method has the advantage of being able to
use high gain IGBTs which do not have any inherent
short circuit capability. Current sense IGBTs work as
well as current sense MOSFETs in most circumstances.
However, the basic problem of working with very low
sense voltages still exists. Sense IGBTs sense current
through the channel and are therefore linear with re-
spect to the collector current. Because IGBTs have a
very low incremental on−resistance, sense IGBTs be-
have much like low−on resistance current sense MOS-
FETs. The output voltage of a properly terminated sense
IGBT is very low, normally less than 100 mV.
The sense IGBT approach requires fault blanking to
prevent false tripping during turn−on. The sense IGBT
also requires that the sense signal is ignored while the
gate is low. This is because the mirror output normally
produces large transient voltages during both turn−on
and turn−off due to the collector to mirror capacitance.
With non−sensing types of IGBTs, a low resistance cur-
rent shunt (5.0 to 50 mΩ) can be used to sense the emit-
ter current. When the output is an actual short circuit,
the inductance will be very low. Since the blanking cir-
cuit provides a fixed minimum on−time, the peak cur-
rent under a short circuit can be very high. A short cir-
cuit discern function is implemented by the second
comparator which has a higher trip voltage. The short
circuit signal is latched and appears at the Fault Output.
When a short circuit is detected, the IGBT should be
turned−off for several milliseconds allowing it to cool
down before it is turned back on. The sense circuit is
very similar to the desaturation circuit. It is possible to
build a combination circuit that provides protection for
both Short Circuit capable IGBTs and Sense IGBTs.
Rev. 02