Functional description

TD350E

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Doc ID 018539 Rev 2

5

Functional description

5.1

Input

The input is compatible with optocouplers or pulse transformers. The input is triggered by

the signal edge and allows the use of a small-sized, low-cost pulse transformer. Input is

active low (output is high when input is low) to ease the use of the optocoupler. When driven

by a pulse transformer, the input pulse (positive and negative) width must be larger than the

5.2

Voltage reference

A voltage reference is used to create accurate timing for the two-level turn-off with external

resistor and capacitor.

5.3

Desaturation protection

Desaturation protection ensures the protection of the IGBT in the event of overcurrent.

When the DESAT voltage goes higher than 7 V, the output is driven low (with 2-level turn-off,

if applicable). The FAULT output is activated. The FAULT state is exited at the next falling

edge of IN input.

A programmable blanking time is used to allow enough time for IGBT saturation. Blanking

time is provided by an internal current source and external capacitor.

DESAT input can also be used with an external comparator for overcurrent or

overtemperature detection.

5.4

Active Miller clamp

A Miller clamp allows the control of the Miller current during a high dV/dt situation and can

eliminate the need for a negative supply voltage.

During turn-off, the gate voltage is monitored and the clamp output is activated when gate

voltage goes below 2 V (relative to GND). The clamp voltage is VL+3 V max for a Miller

current up to 500 mA. The clamp is disabled when the IN input is triggered again.

5.5

Two-level turn-off

The two-level turn-off is used to increase the reliability of the application.

During turn-off, gate voltage can be reduced to a programmable level in order to reduce the

IGBT current (in the event of overcurrent). This action prevents both dangerous overvoltage

across the IGBT and RBSOA problems, especially at short-circuit turn-off.

timing.

width.