IXDD414CI Ver la hoja de datos (PDF) - IXYS CORPORATION

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IXDD414CI

14 Amp Low-Side Ultrafast MOSFET Driver

IXYS CORPORATION 

APPLICATIONS INFORMATION

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 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 IXDD414 has the unique capability to softly switch off the

high-power MOSFET module, significantly reducing these

Ldi/dt transients.

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.

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

Figure 27 - Application Test Diagram

IXDD414PI/414YI/414CI/414SI

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 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

the VMO580-02F.

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.

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).

In this way, the high-power MOSFET module is softly turned off

by the IXDD414, preventing its destruction.

Ld

10uH

+

VB

-

+ VCC

-

+

VIN

-

IXDD414

VCC

VCCA

IN

EN

GND

GND

OUT

Rsh

1600ohm

Rg

1ohm

Low_Power

2N7002/PLP

R+

10kohm

Rd

0.1ohm

High_Power

VMO580-02F

Rs

Ls

20nH

One Shot Circuit

NOT1

CD4049A

Ros

NAND

CD4011A

NOT2

CD4049A

1Mohm

Cos

1pF

Q

Rcomp

5kohm

Ccomp

1pF

R

Comp

LM339

+

V+

V-

-

+

-

REF

0

C+

100pF

NOT3

CD4049A

NOR1

S

CD4001A

EN

NOR2

CD4001A

SR Flip-Flop

8

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