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IXDN409CI Datasheet(PDF) 8 Page - IXYS Corporation |
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IXDN409CI Datasheet(HTML) 8 Page - IXYS Corporation |
8 / 10 page 8 IXDD409PI / 409SI / 409YI / 409CI IXDI409PI / 409SI / 409YI / 409CI IXDN409PI / 409SI / 409YI / 409CI 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 µs 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 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 VGS/dt gate 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 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 CC 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 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. APPLICATIONS INFORMATION Figure 26 - Application Test Diagram 10uH Ld 0.1ohm Rd Rs 20nH Ls 1ohm Rg 10kohm R+ VMO580-02F High_Power 5kohm Rcomp 100pF C+ + - V+ V- Comp LM339 1600ohm Rsh Ccomp 1pF VCC VCCA IN EN GND SUB OUT IXDD409 + - VIN + - VCC + - REF + - VB CD4001A NOR2 1Mohm Ros NOT2 CD4049A CD4011A NAND CD4049A NOT1 CD4001A NOR1 CD4049A NOT3 Low_Power 2N7002/PLP 1pF Cos 0 S R EN Q One ShotCircuit SR Flip-Flop |
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