ST AN2002 APPLICATION NOTE

AN2002

APPLICATION NOTE

Usin g the Demoboard for the TD350 Advanc ed IGBT Driver

1 Introduction

TD350 is an advanced I GBT/MOSFE T driver with integrated cont rol and protection functi ons. Principles
of operation and application examples for the TD350 are described extensively in application note
AN1944. The presen t application note con cerns the characteristics a nd use of the dem oboard available
for testing the TD350.

Figure 1: TD350 pinout

1

VREF

IN

2

14

13

DESAT

VH

NC

COFF

NC

LVOFF

3FAULT

4

5

6

7

date code

TD350I

12

11

10

9

8

OUT

OUTL

VL

CLAMP

GND

Bevelled edg e
indicates pin 1

location

2 Printed circuit board presentation

The demoboard is a 26x35mm double-sided PCB with the TD350 and its peripheral components
mounted in a typical configuration (pictured in Figure 2). To aid in the understanding and easy
modification of the board, the PCB top-side and bottom-side layers, as well as the silk-screen previews
are shown i n Figure 3.

The demoboard electrical schematic is presented on Figure 4, and the associate d bi ll o f material can be
found on Table 1 on page 5.

Let’s study step by step the demoboard original configuration, and the way it can be modified to be
adapted to the application.

July 2004

Revision A 1/8

AN2002 Using the Demoboard for the TD350 Advanced IGBT Driver

Figure 2: Demoboard layout

Figure 3: Demoboard PCB: Silk-screen, top-layer an d bottom -layer previews

2.1 Input stage

The TD350 can be drive n by either a pulse transformer or an optocoupler. The dem oboard is set up to
use an optoc oupler. The T D350 IN pin i s clamped t o 5V by a zener diode D2 and its bleeding resistor
R11=10K (see demoboa rd schematic on Fi gure 4). To interface the demoboard with the system, the IN1
pin of the input connector can simply be connected to a low-side optocoupler, as show on Figure 5. An
optional filtering capacitor can be added (for instance 47pF) in the event of a highly noisy environment,
although the TD350 already includes a filtering o n input signals and reject s signals smaller than 1 00ns

specification).

(t

onmin

The demoboard can be modified to be driven by a pulse transformer by implementing the optional
components R2, R3, R4 and C8. The principle of operation with a pulse transformer is explained in
AN1944.

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Using the Demoboard for the TD350 Advanced IGBT Driver AN2002

VH

GNDVLOUTL

2.2 Output stage

The TD350 uses separate sink and source outputs (OUTL/OUTH ) for easy gate driving. The integrated

circuit output stage is able to sink/source about 2A/1.5A typical at 25°C, but the IGBT turn-on and turn-off
current can be limited independently by the g ate resistors R6 and R7 includ ed on the demoboard. The
original value for these resistors are R6=R7=47R.

Output current capability can be increased by using an external buffer with two low-cost bipolar
transistors. This configuration is described in Section 4 on page 7.

2.3 Active Miller Clamp

The TD350 offers an alternative solution to the problem of the Miller current in IGBT switching
applications. Instead of driving the IGBT gate to a negative voltage to increase the safety margin, the
TD350 uses a dedicated CLAMP pin to control the Miller current. When the IGBT is off, a low impedance
path is established between IGBT gate and em itter to carry the Miller current, and the voltage spike on
the IGBT gate is greatly reduced. The CLAMP switch is opened when the input is activated and is closed
when the actua l gate voltage goes close to the ground level. In th is way, the CLAMP funct ion doesn’t
affect the turn-off characteristic, but only keeps the gate to the low level throughout the off time.

On the demoboard, the CLAMP pin is connected to the IGBT gate by strap R9. This strap can be
removed when the clamp feature is not needed, or when an external buffer is used (see reference
schematic on Figure 6).

Figure 4: Demoboard PCB: Electrical Schematic

VH

R6

R7

C1

C3

C5 C7

R1

VH

C6

R9

VL

1

2

3

4

Desat

Out

Gnd

Clamp

Gnd

Fault

Gnd

Lvoff

In2

VH

In1

R2*

1

2

3

4

5

6

7

VL

VL

8

C8*

VH

R3*

C2VH

R4*

R5

VREF

R8

C4

R10

D1

(*): optional parts not m ounted on demoboard original configurati on

R11

D2

TD350

IN

1

VREF

2

FAULT

3

NC

4

COFF

5

NC

6

LVOFF

7

DESAT

OUTH

CLAMP

14

13

12

11

10

9

8

2.4 2-level turn-off

In the event of a short-circuit or overcurrent in the load, a large voltage overshoot can occur across the
IGBT at turn-off and can ex ceed t he IGB T breakdown voltage. By reducing the ga te voltag e bef ore turn­off, the IGBT current i s limited a nd the pote ntial overvoltage is redu ced. Thi s technique is called 2-level
turn-off. Both the level and duration of the intermediate off level are adjustable. Duration is set by the
external resistor R8 and capacitor C4 i n conjunction with the integrated voltage reference for accurat e

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