VLA500-01
Hybrid IC IGBT Gate Driver +
DC/DC Converter
Powerex, Inc., 200 E. Hillis Street, Youngwood, Pennsylvania 15697-1800 (724) 925-7272
6 Rev. 2/08
General Description
The VLA500-01 is a hybrid integrated circuit designed to
provide gate drive for high power IGBT modules. This
circuit has been optimized for use with Powerex NF-
Series and A-Series IGBT modules. However, the
output characteristics are compatible with most MOS
gated power devices. The VLA500-01 features a com-
pact single-in-line package design. The upright mount-
ing minimizes required printed circuit board space to
allow efficient and flexible layout. The VLA500-01
converts logic level control signals into fully isolated
+15V/-8V gate drive with up to12A of peak drive current.
Isolated drive power is provided by a built in DC-to-DC
converter and control signal isolation is provided by an
integrated high speed opto-coupler. Short circuit protec-
tion is provided by means of destauration detection.
Short Circuit Protection
Figure 1 shows a block diagram of a typical desatura-
tion detector. In this circuit, a high voltage fast recovery
diode (D1) is connected to the IGBT’s collector to moni-
tor the collector to emitter voltage. When the IGBT is in
the off state, V
CE
is high and D1 is reverse biased. With
D1 off the (+) input of the comparator is pulled up to
the positive gate drive power supply (V+) which is nor-
mally +15V. When the IGBT turns on, the comparators
(+) input is pulled down by D1 to the IGBT’s V
CE(sat)
.
The (-) input of the comparator is supplied with a fixed
voltage (V
trip
). During a normal on-state condition the
comparator’s (+) input will be less than V
trip
and it’s out-
put will be low. During a normal off-state condition the
comparator’s (+) input will be larger than V
trip
and it’s out-
put will be high. If the IGBT turns on into a short circuit,
the high current will cause the IGBT’s collector-emitter
voltage to rise above V
trip
even though the gate of the
IGBT is being driven on. This abnormal presence of
high V
CE
when the IGBT is supposed to be on is often
called desaturation. Desaturation can be detected by
a logical AND of the driver’s input signal and the com-
parator output. When the output of the AND goes high
a short circuit is indicated. The output of the AND can
be used to command the IGBT to shut down in order
to protect it from the short circuit. A delay (t
trip
) must be
provided after the comparator output to allow for the nor-
mal turn on time of the IGBT. The t
trip
delay is set so
that the IGBT's V
CE
has enough time to fall below V
trip
during normal turn on switching. If t
trip
is set too short,
erroneous desaturation detection will occur. The maxi-
mum allowable t
trip
delay is limited by the IGBT’s short
circuit withstanding capability. In typical applications
using Powerex IGBT modules the recommended limit is
10µs.
Operation of the VLA500-01 Desaturation Detector
The Powerex VLA500-01 incorporates short circuit
protection using desaturation detection as described
above. A flow chart for the logical operation of the short-
circuit protection is shown in Figure 2. When a desatura-
tion is detected the hybrid gate driver performs a soft
shutdown of the IGBT and starts a timed (t
timer
) 1.5ms
lock out. The soft turn-off helps to limit the transient
voltage that may be generated while interrupting the
large short circuit current flowing in the IGBT. During the
lock out the driver pulls Pin 28 low to indicate the fault
status. Normal operation of the driver will resume after
the lock-out time has expired and the control input signal
returns to its off state.
Adjustment of Trip Time
The VLA500-01 has a default short-circuit detection
time delay (t
trip
) of approximately 3µs. This will prevent
erroneous detection of short-circuit conditions as long
as the series gate resistance (R
G
) is near the mini-
mum recommended value for the module being used.
The 3µs delay is appropriate for most applications so
adjustment will not be necessary. However, in some low
frequency applications it may be desirable to use a
larger series gate resistor to slow the switching of
the IGBT, reduce noise, and limit turn-off transient
GATE
DRIVE
IGBT
MODULE
AND
INPUT
V+
D1
V
trip
C
E
G
E
R
G
DELAY
t
trip
COMPARE
SHUTDOWN
+
Figure 1. Desaturation Detector
