IL33153 Datasheet, PDF (10/14 Pages) Integral Corp. – SINGLE IGBT GATE DRIVER

IL33153
Optoisolator Output Fault
The IL33153 has an active high fault output. The
fault output may be easily interfaced to an optoisolator.
While it is important that all faults are properly reported,
it is equally important that no false signals are propa-
gated. Again, a high dv/dt optoisolator should be used.
The LED drive provides a resistor programmable
current of 10 to 20 mA when on, and provides a low
impedance path when off. An active high output, resistor,
and small signal diode provide an excellent LED driver.
This circuit is shown in Figure 33.
Figure 33. Output Fault Optoisolator
UNDERVOLTAGE LOCKOUT
It is desirable to protect an IGBT from insufficient
gate voltage. IGBTs require 15 V on the gate to achieve
the rated on−voltage. At gate voltages below 13 V, the
on−voltage increases dramatically, especially at higher
currents. At very low gate voltages, below 10 V, the
IGBT may operate in the linear region and quickly
overheat. Many PWM motor drives use a bootstrap sup-
ply for the upper gate drive. The UVLO provides pro-
tection for the IGBT in case the bootstrap capacitor dis-
charges.
The IL33153 will typically start up at about 12 V.
The UVLO circuit has about 1.0 V of hysteresis and will
disable the output if the supply voltage falls below about
11 V.
PROTECTION CIRCUITRY
Desaturation Protection
Bipolar Power circuits have commonly used what is
known as “Desaturation Detection”. This involves moni-
toring the collector voltage and turning off the device if
this voltage rises above a certain limit. A bipolar transis-
tor will only conduct a certain amount of current for a
given base drive. When the base is overdriven, the de-
vice is in saturation. When the collector current rises
above the knee, the device pulls out of saturation. The
maximum current the device will conduct in the linear
region is a function of the base current and the dc cur-
rent gain (hFE) of the transistor.
The output characteristics of an IGBT are similar to
a Bipolar device. However, the output current is a func-
tion of gate voltage instead of current. The maximum
current depends on the gate voltage and the device type.
IGBTs tend to have a very high transconductance and a
much higher current density under a short circuit than a
bipolar device. Motor control IGBTs are designed for a
lower current density under shorted conditions and a
longer short circuit survival time.
The best method for detecting desaturation is the use
of a high voltage clamp diode and a comparator. The
IL33153 has a Fault Blanking/Desaturation Comparator
which senses the collector voltage and provides an out-
put indicating when the device is not fully saturated.
Diode D1 is an external high voltage diode with a rated
voltage comparable to the power device. When the
IGBT is “on” and saturated, D1 will pull down the volt-
age on the Fault Blanking/Desaturation Input. When the
IGBT pulls out of saturation or is “off”, the current
source will pull up the input and trip the comparator.
The comparator threshold is 6.5 V, allowing a maximum
on−voltage of about 5.8 V.
A fault exists when the gate input is high and VCE is
greater than the maximum allowable VCE(sat). The out-
put of the Desaturation Comparator is ANDed with the
gate input signal and fed into the Short Circuit and
Overcurrent Latches. The Overcurrent Latch will
turn−off the IGBT for the remainder of the cycle when a
fault is detected. When input goes high, both latches are
reset. The reference voltage is tied to the Kelvin Ground
instead of the VEE to make the threshold independent of
negative gate bias. Note that for proper operation of the
Desaturation Comparator and the Fault Output, the Cur-
rent Sense Input must be biased above the Overcurrent
and Short Circuit Comparator thresholds. This can be
accomplished by connecting Pin 1 to VCC.
Figure 34. Desaturation Detection
The IL33153 also features a programmable fault
blanking time. During turn−on, the IGBT must clear the
opposing free−wheeling diode. The collector voltage
will remain high until the diode is cleared. Once the
diode hasbeen cleared, the voltage will come down
quickly to the VCE(sat) of the device. Following turn−on,
there is normally considerable ringing on the collector
due to the COSS capacitance of the IGBTs and the para-
Rev. 02