ACPL-333J-000E 데이터 시트보기 (PDF) - Avago Technologies
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ACPL-333J-000E Datasheet PDF : 23 Pages
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Output Control
The outputs (VOUT and FAULT) of the ACPL-333J are con-
trolled by the combination of IF, UVLO and a detected
IGBT Desat condition. Once UVLO is not active (VCC2 -
VE > VUVLO), VOUT is allowed to go high, and the DESAT
(pin 14) detection feature of the ACPL-333J will be the
primary source of IGBT protection. Once VCC2 is increased
from 0V to above VUVLO+, DESAT will remain functional
until VCC2 is decreased below VUVLO-. Thus, the DESAT
detection and UVLO features of the ACPL-333J work in
conjunction to ensure constant IGBT protection.
Desaturation Detection and High Current Protection
The ACPL-333J satisfies these criteria by combining a
high speed, high output current driver, high voltage
optical isolation between the input and output, local
IGBT desaturation detection and shut down, and an
optically isolated fault status feedback signal into a single
16-pin surface mount package.
The fault detection method, which is adopted in the
ACPL-333J, is to monitor the saturation (collector)
voltage of the IGBT and to trigger a local fault shutdown
sequence if the collector voltage exceeds a predeter-
mined threshold. A small gate discharge device slowly
reduces the high short circuit IGBT current to prevent
damaging voltage spikes. Before the dissipated energy
can reach destructive levels, the IGBT is shut off. During
the off state of the IGBT, the fault detect circuitry is simply
disabled to prevent false ‘fault’ signals.
The alternative protection scheme of measuring IGBT
current to prevent desaturation is effective if the short
circuit capability of the power device is known, but
this method will fail if the gate drive voltage decreases
enough to only partially turn on the IGBT. By directly
measuring the collector voltage, the ACPL-333J limits the
power dissipation in the IGBT even with insufficient gate
drive voltage. Another more subtle advantage of the de-
saturation detection method is that power dissipation in
the IGBT is monitored, while the current sense method
relies on a preset current threshold to predict the safe
limit of operation. Therefore, an overly conservative over
current threshold is not needed to protect the IGBT.
Slow IGBT Gate Discharge during Fault Condition
When a desaturation fault is detected, a weak pull-down
device in the ACPL-333J output drive stage will turn on
to ‘softly’ turn off the IGBT. This device slowly discharges
the IGBT gate to prevent fast changes in drain current
that could cause damaging voltage spikes due to lead
and wire inductance. During the slow turn off, the large
output pull-down device remains off until the output
voltage falls below VEE + 2 Volts, at which time the large
pull down device clamps the IGBT gate to VEE.
DESAT Fault Detection Blanking Time
The DESAT fault detection circuitry must remain disabled
for a short time period following the turn-on of the IGBT
to allow the collector voltage to fall below the DESAT
threshold. This time period, called the DESAT blanking
time is controlled by the internal DESAT charge current,
the DESAT voltage threshold, and the external DESAT
capacitor.
The nominal blanking time is calculated in terms of
external capacitance (CBLANK), FAULT threshold voltage
(VDESAT), and DESAT charge current (ICHG) as tBLANK =
CBLANK x VDESAT / ICHG. The nominal blanking time with
the recommended 100pF capacitor is 100pF * 6.5 V / 240
μA = 2.7 μsec.
The capacitance value can be scaled slightly to adjust the
blanking time, though a value smaller than 100 pF is not
recommended. This nominal blanking time represents
the longest time it will take for the ACPL-333J to respond
to a DESAT fault condition. If the IGBT is turned on while
the collector and emitter are shorted to the supply rails
(switching into a short), the soft shut-down sequence
will begin after approximately 3 μsec. If the IGBT collector
and emitter are shorted to the supply rails after the IGBT
is already on, the response time will be much quicker due
to the parasitic parallel capacitance of the DESAT diode.
The recommended 100pF capacitor should provide
adequate blanking as well as fault response times for
most applications.
IF
UVLO(VCC2-VE)
ON
Active
ON
Not Active
ON
Not Active
OFF
Active
OFF
Not Active
DESAT Function
Not Active
Active (with DESAT fault)
Active (no DESAT fault)
Not Active
Not Active
Pin 3 (FAULT) Output
VOUT
High
Low
Low (FAULT)
Low
High (or no fault)
High
High
Low
High
Low
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