HCPL316J500E AVAGO TECH, HCPL316J500E Datasheet - Page 23

• Manufacturer Part Number: HCPL316J500E
• Manufacturer: AVAGO TECH

Slow IGBT Gate Discharge During Fault Condition
When a desaturation fault is detected, a weak pull-down
device in the HCPL-316J 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 V
pull down device clamps the IGBT gate to V
DESAT Fault Detection Blanking Time
The DESAT fault detection circuitry must remain dis-
abled for a short time period following the turn-on
of the IGBT to allow the collector voltage to fall below
the DESAT theshold. 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 calcu-
lated in terms of external capacitance (C
threshold voltage (V
(I
nominal blanking time with the recommended 100 pF
capacitor is 100 pF * 7 V / 250 µA = 2.8 µsec. The capaci-
tance value can be scaled slightly to adjust the blanking
time, though a value smaller than 100 pF is not recom-
mended. This nominal blanking time also represents the
longest time it will take for the HCPL-316J 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 collec-
tor and emitter are shorted to the supply rails after the
IGBT is already on, the response time will be much quick-
er due to the parasitic parallel capacitance of the DESAT
diode. The recommended 100 pF capacitor should pro-
vide adequate blanking as well as fault response times
for most applications.
23
CHG
) as
t
BLANK
EE
DESAT
+ 2 Volts, at which time the large
= C
), and DESAT charge current
BLANK
x V
DESAT
BLANK
EE
.
/ I
CHG
), FAULT
. The
Under Voltage Lockout
The HCPL-316J Under Voltage Lockout (UVLO) feature is
designed to prevent the application of insufficient gate
voltage to the IGBT by forcing the HCPL-316J output low
during power-up. IGBTs typically require gate voltages
of 15 V to achieve their rated V
voltages below 13 V typically, their 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. The UVLO function
causes the output to be clamped whenever insufficient
operating supply (V
V
clamp is released to allow the device output to turn on
in response to input signals. As V
(at some level below V
circuitry becomes active. As V
(above V
time the UVLO clamp is released, the DESAT protection
is already active. Therefore, the UVLO and DESAT FAULT
DETECTION features work together to provide seamless
protection regardless of supply voltage (V
UVLO+
(the positive-going UVLO threshold), the UVLO
UVLO+
), the UVLO clamp is released. Before the
CC2
UVLO+
) is applied. Once V
), first the DESAT protection
CC2
CC2
CE(ON)
is further increased
is increased from 0 V
voltage. At gate
CC2
CC2
).
exceeds