MC33153

8

MOTOROLA ANALOG IC DEVICE DATA

–60

10

1.0

80

5.0

10

TA, AMBIENT TEMPERATURE (°C)

VCC = 15 V

VPin 4 = VCC

Drive Output Open

f, INPUT FREQUENCY (kHz)

VCC = 15 V

TA = 25°C

Figure 27. Supply Current versus

Supply Voltage

VCC, SUPPLY VOLTAGE (V)

Figure 28. Supply Current versus Temperature

Output High

Figure 29. Supply Current versus Input Frequency

Output Low

TA = 25°C

CL = 10 nF

= 5.0 nF

= 2.0 nF

= 1.0 nF

8.0

6.0

4.0

2.0

0

20

40

60

80

100

120

140

20

–20

0

–40

10

15

8.0

6.0

4.0

2.0

0

1000

10

100

60

40

20

0

OPERATING DESCRIPTION

GATE DRIVE

Controlling Switching Times

The most important design aspect of an IGBT gate drive is

optimization of the switching characteristics. The switching

characteristics are especially important in motor control

applications in which PWM transistors are used in a bridge

configuration. In these applications, the gate drive circuit

components should be selected to optimize turn–on, turn–off

and off–state impedance. A single resistor may be used to

control both turn–on and turn–off as shown in Figure 30.

However, the resistor value selected must be a compromise

in turn–on abruptness and turn–off losses. Using a single

resistor is normally suitable only for very low frequency

PWM. An optimized gate drive output stage is shown in

Figure 31. This circuit allows turn–on and turn–off to be

optimized separately. The turn–on resistor, Ron, provides

control over the IGBT turn–on speed. In motor control

circuits, the resistor sets the turn–on di/dt that controls how

fast the free–wheel diode is cleared. The interaction of the

IGBT and free–wheeling diode determines the turn–on dv/dt.

Excessive turn–on dv/dt is a common problem in half–bridge

circuits. The turn–off resistor, Roff, controls the turn–off speed

and ensures that the IGBT remains off under commutation

stresses. Turn–off is critical to obtain low switching losses.

While IGBTs exhibit a fixed minimum loss due to minority

carrier recombination, a slow gate drive will dominate the

turn–off losses. This is particularly true for fast IGBTs. It is

also possible to turn–off an IGBT too fast. Excessive turn–off

speed will result in large overshoot voltages. Normally, the

turn–off resistor is a small fraction of the turn–on resistor.

The MC33153 contains a bipolar totem pole output stage

that is capable of sourcing 1.0 amp and sinking 2.0 amps

peak. This output also contains a pull down resistor to ensure

that the IGBT is off whenever there is insufficient VCC to the

MC33153.

In a PWM inverter, IGBTs are used in a half–bridge

configuration. Thus, at least one device is always off. While

the IGBT is in the off–state, it will be subjected to changes in

voltage caused by the other devices. This is particularly a

problem when the opposite transistor turns on.