cd00040938

AN2002
APPLICATION NOTE
Using the Demoboard for the TD350 Advanced IGBT Driver
1
Introduction
TD350 is an advanced IGBT/MOSFET driver with integrated control and protection functions. Principles
of operation and application examples for the TD350 are described extensively in application note
AN1944. The present application note concerns the characteristics and use of the demoboard available
for testing the TD350.
Figure 1: TD350 pinout
14 DESAT
VREF
2
13 VH
FAULT
3
12 OUT
NC
4
11 OUTL
COFF
5
NC
6
LVOFF
7
TD350I
1
date code
2
IN
Bevelled edge
indicates pin 1
location
10 VL
9
CLAMP
8
GND
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 in Figure 3.
The demoboard electrical schematic is presented on Figure 4, and the associated bill of 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
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AN2002
Using the Demoboard for the TD350 Advanced IGBT Driver
Figure 2: Demoboard layout
Figure 3: Demoboard PCB: Silk-screen, top-layer and bottom-layer previews
2.1 Input stage
The TD350 can be driven by either a pulse transformer or an optocoupler. The demoboard is set up to
use an optocoupler. The TD350 IN pin is clamped to 5V by a zener diode D2 and its bleeding resistor
R11=10K (see demoboard schematic on Figure 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 on input signals and rejects signals smaller than 100ns
(tonmin specification).
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
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 gate resistors R6 and R7 included 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 emitter 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 actual gate voltage goes close to the ground level. In this way, the CLAMP function 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
R11
R2*
R1
D2
C8*
C1
R3*
In2 1
VH
TD350
VH
C2
R4*
VH 2
Gnd 3
1
IN
2
VREF
3
DESAT 14
VH
13
FAULT
OUTH
12
4
NC
OUTL
11
5
COFF
VL
10
6
NC
CLAMP
9
7
LVOFF
GND
8
C3
R5
In1 4
VREF
Fault 5
R8
Gnd 6
VH
C4
VL 7
VL
C6
1 Desat
R6
2 Out
R7
3 Gnd
C5
4 Clamp
C7
R9
R10
Lvoff 8
VL
D1
(*): optional parts not mounted on demoboard original configuration
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 exceed the IGBT breakdown voltage. By reducing the gate voltage before turnoff, the IGBT current is limited and the potential overvoltage is reduced. This 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 in conjunction with the integrated voltage reference for accurate
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AN2002
Using the Demoboard for the TD350 Advanced IGBT Driver
timing. The level can be easily set by an external Zener diode D1, and its value is chosen depending on
the IGBT characteristics. This 2-level turn-off sequence takes place at each cycle, it has no effect if the
current doesn’t exceed the normal maximum rated value, but protects the IGBT in case of overcurrent
(with a slight increase of conduction losses).
In the demoboard original configuration, Ta (duration of the intermediate level) is set to approximately
1.5µs by R8=4K7 and C4=470pF. The intermediate level is set by 10V Zener diode D1 and bleeding
resistor R11=10K.
Tip:
How can you inhibit 2-level turn-off?
Connect LVOFF to VH by replacing R10 by a short-circuit, remove C4 capacitor and keep
COFF pin connected to Vref by R8=4K7.
2.5 Desaturation protection feature
The desaturation function provides a protection against overcurrent events. Voltage across the IGBT is
monitored, and the IGBT is turned off if the voltage threshold is reached. A blanking time, tb, is set using
an internal 250mA current source and an external capacitor C1. The DESAT pin is connected to output
demoboard connector by R1 resistor. In order to implement the desaturation feature, an external high
voltage diode (1kV or more) should be connected between the IGBT collector and the demoboard output
connector pin 1 (see Figure 6 for reference schematic).
The high voltage diode blocks the high voltage during IGBT off state. This diode doesn’t need to be fast,
a standard 1kV (or more) diode is acceptable.
During operation, the DESAT capacitor is discharged when TD350 output is low (IGBT off). When the
IGBT is turned on, the DESAT capacitor starts charging and desaturation protection is effective after the
blanking time, tb, has elapsed:
C1
t b = 7.2V Þ -----------------250µA
With the capacitor used in the demoboard (C1=100pF), the blanking time value will be close to 3ms.
Tip:
4/8
What should one do with the DESAT pin when it isn’t used?
Connect DESAT to GND by shorting together pin 1 and pin 3 on the demoboard output
connector (see Figure 5).
Using the Demoboard for the TD350 Advanced IGBT Driver
AN2002
Table 1: Bill of materials for demoboard
Designator
Description
Value
Package
R1
desaturation resistor
1K-1%
0805
C1
desaturation filtering capacitor
100pF-X7R
0805
C3
positive supply ceramic decoupling capacitor
100nF-X7R
0805
C5
negative supply ceramic decoupling capacitor
100nF-X7R
0805
C6
positive supply electrolytic capacitor
47µF-50V
d6.3 x h7.7
C7
negative supply electrolytic capacitor
47µF-50V
d6.3 x h7.7
R6
turn-on gate drive resistor
47R-1%
0805
R7
turn-off gate drive resistor
47R-1%
0805
R9
strap (optional)
0R
0805
R11
bleeding resistor for Zener diode D2
10K-1%
0805
C2
Vref decoupling capacitor
10nF-X7R
0805
R5
FAULT pin pull-up resistor
10K-1%
0805
R8
2-level turn-off timing resistor
4K7-1%
0805
C4
2-level turn-off timing capacitor
470pF-X7R
0805
R10
bleeding resistor for Zener diode D1
10K-1%
0805
D1
Zener diode for 2-level turn-off intermediate level programming
10V
Melf
D2
Zener diode for IN pin level
5V1
Melf
U1
IGBT/MOSFET driver
TD350
SO-14
J1
Input connector
8-lead
J2
Output connector
4-lead
C8
Vref/2 filtering capacitor
not mounted
0805
R4
Vref/2 divider bridge lower resistor (only with pulse transformer)
not mounted
0805
R3
Vref/2 divider bridge upper resistor (only with pulse transformer)
not mounted
0805
R2
adjustment resistor (only with pulse transformer)
not mounted
0805
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AN2002
3
Using the Demoboard for the TD350 Advanced IGBT Driver
Application example no. 1
This first application example demonstrates the typical configuration in which TD350 can be used in low
and medium power applications. In this configuration, the TD350 is able to drive IGBTs with current
ratings up to about 50A. The schematic showing how to connect the demoboard to the optocoupler,
power supply and IGBT module is presented on Figure 5. The demoboard doesn’t require any
modification in order to be used in this configuration. However, it should be noted that C5 and C7
(decoupling capacitors for negative supply) are not needed in this example and they could be removed to
optimize application cost and PCB space.
The main characteristics of this example are:
l Single Supply: with the benefit of the Active Miller Clamp feature, negative supply isn’t needed to
avoid mistriggering of the IGBT at turn-off
l Active Miller Clamp: the feature is implemented on the demoboard by connecting TD350 CLAMP
pin to the IGBT gate with R9=0R resistor
l 2-Step Turn-Off: at turn-off the gate-to-source voltage will be lowered to 10V during approximately
1.5µs to reduce over-voltage stress on the IGBT in case of over-current event
l DESAT not used: to simplify the design DESAT pin is connected to GND to inhibit the function. To
implement the desaturation protection, see Section 2.5.
Figure 5: TD350 demoboard used in basic application
1 In2
16V
TD350 demoboard
2 VH
3 Gnd
4 In1
Out 2
6 Gnd
Gnd 3
7 VL
47pF*
8 Lvoff
(*): optional parts
6/8
Desat 1
5 Fault
Clamp 4
Using the Demoboard for the TD350 Advanced IGBT Driver
4
AN2002
Application example no.2
This second application example shows the typical configuration in which the TD350 can be used in high
power applications. With the use of an additional buffer, the TD350 can drive IGBTs with a current rating
above 100A. The schematic in Figure 6 shows how to connect the demoboard with the optocoupler and
the power supplies on the input side, and with the IGBT module and the gate buffer circuit on the output
side.
The demoboard needs a few modifications with respect to its original configuration to be used as shown
in this example:
1) The R9 strap should be removed.
2) The resistors R6 and R7 should be replaced by short-circuits.
The main characteristics of this example are:
l A dual supply +16V/-10V is used as often needed in high power applications,
l Output buffer stage: considering the high value of the IGBT gate capacitance, the TD350 output is
connected to a discrete buffer stage made of two complementary bipolar transistors,
l CLAMP used as secondary gate discharge: the CLAMP pin is connected to a external buffer to
feature a secondary gate discharge,
l DESAT feature is implemented.
Figure 6: TD350 demoboard used in high power applications
1kV
diode
1 In2
16V
VH
TD350 demoboard
2 VH
T1
3 Gnd
4 In1
10V
47pF*
Desat 1
5 Fault
Out 2
6 Gnd
Gnd 3
7 VL
8 Lvoff
Clamp 4
T2
VL
(*): optional parts
T3
VL
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AN2002
Using the Demoboard for the TD350 Advanced IGBT Driver
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the
consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from
its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications
mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information
previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or
systems without express written approval of STMicroelectronics.
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