IXDD414PI/414YI/414CI
APPLICATIONS INFORMATION
Short Circuit di/dt Limit
ground. (Those glitches might cause false triggering of the
comparator).
A short circuit in a high-power MOSFET module such as the
VM0580-02F, (580A, 200V), as shown in Figure 26, can cause
the current through the module to flow in excess of 1500A for
10µs or more prior to self-destruction due to thermal runaway.
For this reason, some protection circuitry is needed to turn off
the MOSFET module. However, if the module is switched off
too fast, there is a danger of voltage transients occuring on the
drain due to Ldi/dt, (where L represents total inductance in
series with drain). If these voltage transients exceed the
MOSFET's voltage rating, this can cause an avalanche break-
down.
The comparator's output should be connected to a SRFF(Set
Reset Flip Flop). The flip-flop controls both the Enable signal,
andthelowpowerMOSFETgate. PleasenotethatCMOS4000-
series devices operate with a VCC range from 3 to 15 VDC, (with
18 VDC being the maximum allowable limit).
A low power MOSFET, such as the 2N7000, in series with a
resistor, will enable the VMO580-02F gate voltage to drop
gradually. The resistor should be chosen so that the RC time
constant will be 100us, where "C" is the Miller capacitance of
theVMO580-02F.
TheIXDD414hastheuniquecapabilitytosoftlyswitchoffthe
high-power MOSFET module, significantly reducing these
Ldi/dttransients.
For resuming normal operation, a Reset signal is needed at
the SRFF's input to enable the IXDD414 again. This Reset can
be generated by connecting a One Shot circuit between the
IXDD414 Input signal and the SRFF restart input. The One Shot
will create a pulse on the rise of the IXDD414 input, and this
pulse will reset the SRFF outputs to normal operation.
Thus, the IXDD414 helps to prevent device destruction from
both dangers; over-current, and avalanche breakdown due to
di/dt induced over-voltage transients.
The IXDD414 is designed to not only provide ±14A under
normal conditions, but also to allow it's output to go into a high
impedance state. This permits the IXDD414 output to control
a separate weak pull-down circuit during detected overcurrent
shutdown conditions to limit and separately control dVGS/dt gate
turnoff. This circuit is shown in Figure 27.
When a short circuit occurs, the voltage drop across the low-
value, current-sensing resistor, (Rs=0.005 Ohm), connected
between the MOSFET Source and ground, increases. This
triggers the comparator at a preset level. The SRFF drives a low
input into the Enable pin disabling the IXDD408 output. The
SRFF also turns on the low power MOSFET, (2N7000).
Referring to Figure 27, the protection circuitry should include
a comparator, whose positive input is connected to the source
of the VM0580-02. A low pass filter should be added to the input
of the comparator to eliminate any glitches in voltage caused
by the inductance of the wire connecting the source resistor to
In this way, the high-power MOSFET module is softly turned off
by the IXDD414, preventing its destruction.
Figure 27 - Application Test Diagram
+
VB
Ld
-
10uH
Rd
IXDD414
0.1ohm
VCC
VCCA
Rg
High_Power
VMO580-02F
OUT
IN
EN
1ohm
Rsh
1600ohm
+
-
+
-
VCC
VIN
GND
SUB
Rs
Low_Power
2N7002/PLP
Ls
R+
10kohm
20nH
One ShotCircuit
0
Rcomp
Comp
LM339
5kohm
+
V+
NAND
CD4011A
NOT2
CD4049A
C+
NOT1
CD4049A
V-
-
100pF
Ccomp
1pF
Ros
+
-
R
1Mohm
REF
Cos
1pF
Q
NOT3
CD4049A
NOR1
CD4001A
S
EN
NOR2
CD4001A
SR Flip-Flop
8
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