Hybrid Power IC Supplies Gate Drive for IGBT Modules

Mar 1, 2002 12:00 PM
By Sam Davis, Editor, Power Electronics Technology

New from Powerex is the M57161L-01 hybrid gate driver IC for the company's 600V and 1200V F-Series IGBT modules. This single IC converts logic level input control signals into ±7A gate drive with suitable on-and-off bias voltages. An integrated high-speed optocoupler isolates the input control signal from the rest of the circuit. Operating from a 15V input, a built-in isolated dc-dc converter supplies +17.4V and -6.5V for the gate drive circuits. Also included are short-circuit and undervoltage protection, as well as a fault status feedback signal.

F-Series (trench gate) IGBT modules have a built-in real time control (RTC) circuit that limits short-circuit current and maintains a 10µs short-circuit withstand capability. It does this by actively reducing the gate voltage in the presence of excessive collector current. The gate driver (Fig. 1) uses a gate voltage detection circuit to sense activation of the RTC circuit.

Activation of the module's RTC causes the gate driver to initiate a soft shutdown of the IGBT and start a timed lock-out — typically 2 ms. Soft turn-off limits any generated transient voltage and interrupts IGBT short-circuit current. During lockout, the gate driver produces a fault feedback signal and ignores all input signals. Normal operation resumes after lockout time expires and the control input signal returns to its off state.

This protection scheme avoids the need for a high voltage detection diode, reduces spacing requirements on the gate driver's p. c. board, and improves noise immunity.

There is a default short-circuit detection time delay of about 3.5µs, which prevents erroneous detection of short-circuit conditions as long as the series gate resistance (R_G) is near the minimum recommended value for the module being used. Some low frequency applications may use a large Rg to slow the switching of the IGBT. In these cases, you can use the td adjust pin (28) to adjust the RTC detection time and total shut-down time. To extend the trip time, you can connect C_TRIP as shown in Fig. 2. This capacitor should be located as close as possible to the pins of the gate driver.

Fig. 2 shows an example application circuit. The input circuit to the optocoupler includes a 390Ω resistor, which provides about 10mA to drive the optocoupler with a 5V input. Other input voltages require the addition of an external current limiting resistor.

The circuit operates from a 15V supply that must be decoupled with a capacitor closely connected to the driver's pins, providing a stable, well-filtered voltage for the primary side of the driver's built-in dc-dc converter.

To deliver an efficient pulse current, the output of the isolated dc-dc converter must be decoupled using a combination of low impedance electrolytic and film capacitors. These capacitors should be located as close as possible to the gate driver's pins.

Detecting a short circuit or undervoltage, pin 28 pulls down to the V_EE supply. An optocoupler isolates the fault feedback signal by connecting the isolated power supply's common pin to the fault signal pin through a 470Ω resistor. If a fault occurs, about 10mA flows in the optocoupler.

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