M57161L-01

Powerex, Inc., 200 E. Hillis Street, Youngwood, Pennsylvania 15697-1800 (724) 925-7272

M57161L-01

Hybrid IC for IGBT Gate Driver

4

1. Principle of Operation – RTC Detection and Short-Circuit Protection

Powerex F-Series (trench gate) IGBT modules have a built-in

RTC (Real Time Control) circuit.

The purpose of the RTC is to limit

short-circuit current and maintain a 10µs short-circuit withstanding

capability. The RTC circuit limits the current by actively reducing the

gate voltage when excessive collector current is present. The M57161L-

01 gate driver uses a gate voltage detection circuit to sense the

activation of the RTC circuit inside the F-Series IGBT module.

A

simplified schematic of the RTC detector circuit is shown in Figure 1.

This circuit consists of a comparator with its (-) input connected

to the gate of the IGBT module and its (+) input supplied with a fixed

comparator output low. In the normal OFF state, the gate voltage is nearly equal to the negative gate drive supply

that the module’s RTC has been activated. This condition is identified by a logical AND of

the gate driver’s control input signal and the comparator’s output as shown in Figure 1.

The output of the AND will go high when a short-circuit condition is detected. The output

of the AND is then used to command the IGBT to shut down in order to protect it from the

short circuit. A delay is provided after the comparators output to prevent the circuit from

indicating a short-circuit condition during the normal transition of gate voltage at turn-on.

2. Operation of the M57161L-01 RTC Detector

The Powerex M57161L-01 hybrid gate drive circuit implements RTC detection as

described above. A flow chart for the logical operation of the short-circuit protection is

shown in Figure 2.

When the IGBT module’s RTC is activated the hybrid gate driver

The soft turn-off helps to limit the transient voltage that may be generated while

interrupting the short-circuit current flowing in the IGBT.

During the lock-out a fault

feedback signal is asserted and all input signals are ignored. Normal operation of the

driver will resume after the lock-out time has expired and the control input signal returns to

its off state.

This protection scheme is superior to conventional desaturation detection because

it avoids the need for a high voltage detection diode, and reduces spacing requirements on

the gate drive printed circuit board. In addition, noise immunity is improved because the

driver is not connected to the high voltage on the IGBT’s collector.

3. Adjusting Protection Delay Time

approximately 3.5µs. This will prevent erroneous detection of short-circuit conditions as

module being used. The 3.5µs delay is appropriate for most applications so adjustment

will not be necessary. However, in some low frequency applications it may be desirable to

use a larger series gate resistance to slow the switching of the IGBT for reduced noise and

RTC

Circuit

C

E

G

+

F-Series

IGBT

Module

E

COMPARE

DELAY

GATE

DRIVE

AND

+

Shut-Down

Input

Figure 1 RTC Detector

Start

Is

Is Input

Signal ON

Delay

Is

Slow Shut-down

Disable Output

Set Fault Signal

Is Input

Signal OFF

Clear Fault

Signal

Enable Output

NO

YES

NO

YES

NO

YES

NO

YES

Figure 2 Flow Chart