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IL33153 Datasheet, PDF (9/14 Pages) Integral Corp. – SINGLE IGBT GATE DRIVER | |||
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IL33153
OPERATING DESCRIPTION
GATE DRIVE
Controlling Switching Times
The most important design aspect of an IGBT gate
drive is optimization of the switching characteristics.
The switching characteristics are especially important in
motor control applications in which PWM transistors are
used in a bridge configuration. In these applications, the
gate drive circuit components should be selected to op-
timize turnâon, turnâoff and offâstate impedance. A
single resistor may be used to control both turnâon and
turnâoff as shown in Figure 31. However, the resistor
value selected must be a compromise in turnâon abrupt-
ness and turnâoff losses. Using a single resistor is nor-
mally suitable only for very low frequency PWM. An
optimized gate drive output stage is shown in Figure 32.
This circuit allows turnâon and turnâoff to be optimized
separately. The turnâon resistor, Ron, provides control
over the IGBT turnâon speed. In motor control circuits,
the resistor sets the turnâon di/dt that controls how fast
the freeâwheel diode is cleared. The interaction of the
IGBT and freeâwheeling diode determines the turnâon
dv/dt. Excessive turnâon dv/dt is a common problem in
halfâbridge circuits. The turnâoff resistor, Roff, controls
the turnâoff speed and ensures that the IGBT remains
off under commutation stresses. Turnâoff is critical to
obtain low switching losses. While IGBTs exhibit a
fixed minimum loss due to minority carrier recombina-
tion, a slow gate drive will dominate the turnâoff losses.
This is particularly true for fast IGBTs. It is also possi-
ble to turnâoff an IGBT too fast. Excessive turnâoff
speed will result in large overshoot voltages. Normally,
the turnâoff resistor is a small fraction of the turnâon
resistor.
The IL33153 contains a bipolar totem pole output
stage that is capable of sourcing 1.0 amp and sinking 2.0
amps peak. This output also contains a pull down resis-
tor to ensure that the IGBT is off whenever there is in-
sufficient VCC to the IL33153.
In a PWM inverter, IGBTs are used in a halfâbridge
configuration. Thus, at least one device is always off.
Whilethe IGBT is in the offâstate, it will be subjected to
changes in voltage caused by the other devices. This is
particularly a problem when the opposite transistor turns
on.
When the lower device is turned on, clearing the up-
per diode, the turnâon dv/dt of the lower device appears
across the collector emitter of the upper device. To
eliminate shootâthrough currents, it is necessary to pro-
vide a low sink impedance to the device that is in the
offâstate. In most applications the turnâoff resistor can
be made small enough to hold off the device that is un-
der commutation without causing excessively fast
turnâoff speeds.
Figure 31. Using a Single Gate Resistor
Figure 32. Using Separate Resistors
for TurnâOn and TurnâOff
A negative bias voltage can be used to drive the
IGBT into the offâstate. This is a practice carried over
from bipolar Darlington drives and is generally not re-
quired for IGBTs. However, a negative bias will reduce
the possibility of shootâthrough. The IL33153 has sepa-
rate pins for VEE and Kelvin Ground. This permits op-
eration using a +15/â5.0 V supply.
INTERFACING WITH OPTOISOLATORS
Isolated Input
The IL33153 may be used with an optically isolated
input. The optoisolator can be used to provide level
shifting, and if desired, isolation from ac line voltages.
An optoisolator with a very high dv/dt capability should
be used, such as the Hewlett Packard HCPL4053. The
IGBT gate turnâon resistor should be set large enough
to ensure that the optoâs dv/dt capability is not exceeded.
Like most optoisolators, the HCPL4053 has an active
low openâcollector output. Thus, when the LED is on,
the output will be low. The IL33153 has an inverting
input pin to interface directly with an optoisolator using
a pullup resistor. The input may also be interfaced di-
rectly to 5.0 V CMOS logic or a microcontroller.
Rev. 02
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