IXDN409 IXYS Corporation, IXDN409 Datasheet - Page 8

• Manufacturer Part Number: IXDN409
• Description: 9 Amp Low-side Ultrafast Mosfet Driver
• Manufacturer: IXYS Corporation

APPLICATIONS INFORMATION
Figure 26 - Application Test Diagram
Short Circuit di/dt Limit
A short circuit in a high-power MOSFET module such as the
VM0580-02F, (580A, 200V), as shown in Figure 25, can cause
the current through the module to flow in excess of 1500A for
10 s 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).
MOSFET's voltage rating, this can cause an avalanche break-
down.
The IXDD409 has the unique capability to softly switch off the
high-power MOSFET module, significantly reducing these
Ldi/dt transients.
Thus, the IXDD409 helps to prevent device destruction from
both dangers; over-current, and avalanche breakdown due to
di/dt induced over-voltage transients.
The IXDD409 is designed to not only provide ±9A under normal
conditions, but also to allow it's output to go into a high
impedance state. This permits the IXDD409 output to control
a separate weak pull-down circuit during detected overcurrent
shutdown conditions to limit and separately control d
turnoff. This circuit is shown in Figure 26.
Referring to Figure 26, 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
EN
If these voltage transients exceed the
One Shot Circuit
CD4049A
NOT1
1Mohm
IXDD409PI / 409SI / 409YI / 409CI IXDI409PI / 409SI / 409YI / 409CI
IXDN409PI / 409SI / 409YI / 409CI
Ros
Cos
1pF
CD4011A
NAND
+
-
VCC
SR Flip-Flop
VGS
CD4049A
CD4049A
NOT2
NOT3
/dt gate
+
-
VIN
Q
8
CD4001A
CD4001A
NOR1
ground. (Those glitches might cause false triggering of the
comparator).
The comparator's output should be connected to a SRFF(Set
Reset Flip Flop). The flip-flop controls both the Enable signal,
and the low power MOSFET gate. Please note that CMOS 4000-
series devices operate with a V
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
the VMO580-02F.
For resuming normal operation, a Reset signal is needed at
the SRFF's input to enable the IXDD409 again. This Reset can
be generated by connecting a One Shot circuit between the
IXDD409 Input signal and the SRFF restart input. The One Shot
will create a pulse on the rise of the IXDD409 input, and this
pulse will reset the SRFF outputs to normal operation.
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 IXDD409 output. The
SRFF also turns on the low power MOSFET, (2N7000).
In this way, the high-power MOSFET module is softly turned off
by the IXDD409, preventing its destruction.
NOR2
VCC
VCCA
IN
EN
GND
SUB
IXDD409
R
S
OUT
Ccomp
Rcomp
5kohm
1pF
1600ohm
Comp
LM339
Rsh
2N7002/PLP
Low_Power
V+
V-
+
-
REF
10kohm
CC
1ohm
+
-
Rg
R+
range from 3 to 15 VDC, (with
10uH
100pF
C+
Ld
0
0.1ohm
20nH
Ls
VMO580-02F
High_Power
Rd
Rs
+
-
VB