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The drive circuit for IGBTs that’s a prizewinner
The SCALE driver is a winning project of the competition
organized by “Technology Center Switzerland 1998”.
And ABB Switzerland AG honored the development of
the SCALE driver by distinguishing it as the “best project
in power electronics 1998”.
The SCALE drivers from CONCEPT are based on a chip set that was
developed specifically for the reliable driving and safe operation of
IGBTs and power MOSFETs.
The name “SCALE” is an acronym for the most outstanding properties of the SCALE
series of drivers:
SCALE = Scaleable, Compact, All purpose, Low cost and Easy to use.
Product Highlights
✔ Suitable for IGBTs and power MOSFETs
✔ Short circuit and overcurrent protection
✔ Extremely reliable, long service life
✔ High gate current from ±6A to ±30A
✔ Electrical isolation from 500V to over 10kV
✔ Electrically isolated status acknowledgement
✔ Monitoring of power supply and self-monitoring
✔ Switching frequency DC to >100kHz
✔ Duty cycle: 0... 100%
✔ High dv/dt immunity, guaranteed >100,000V/µs
✔ Complete with DC/DC converter
Applications
✔ Inverters
✔ Motor drive technology
✔ Traction
✔ Railroad power supplies
✔ Converters
✔ Power engineering
✔ Switched-mode power supplies
✔ Radiology and laser technology
✔ DC/DC converter
✔ Research
✔ RF generators and converters
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Description and Application Manual
Contents
SCALE driver application – it’s never been so simple ........................... 4
A brief introduction ............................................................................ 4
Mode selection and dead times ........................................................................................ 4
Voltage supply and logic level.......................................................................................... 4
Signal inputs and status outputs ........................................................................................ 5
Connecting the IGBTs ...................................................................................................... 5
Defining the turn-off threshold ........................................................................................... 5
Application example: 30kW inverter with six-pack driver .................. 6
What is a “SCALE” driver?.................................................................. 7
Scaleable....................................................................................................................... 7
Compact ........................................................................................................................ 8
All purpose..................................................................................................................... 8
Low cost......................................................................................................................... 8
Easy to use..................................................................................................................... 9
Your benefit: the application advantages of SCALE drivers .................. 9
Reliable operation........................................................................................................... 9
Genuine electrical isolation .............................................................................................. 9
Reliable transformer principle ......................................................................................... 10
Delay times .................................................................................................................. 10
Status acknowledgements .............................................................................................. 10
Ideal layout of the terminals............................................................................................ 10
How exactly do they work? The SCALE drivers in detail .................... 11
Overview ..................................................................................................................... 11
The concept of the SCALE driver circuit............................................................................ 11
Block diagram of the “Logic-to-Driver-Interface” LDI 001 .................................................... 12
The power supply: the integrated DC/DC converter .......................................................... 13
The electronic interface: LDI 001..................................................................................... 13
Block diagram of the “Logic-to-Driver-Interface“ LDI 001 .................................................... 14
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The Intelligent Gate Driver: IGD 001 ............................................................................... 15
Block diagram of the ”Intelligent Gate Driver“ IGD 001 .................................................... 16
Absolute safety: the protection concept............................................. 17
Short circuit and over-current protection ........................................................................... 17
Power supply monitoring................................................................................................ 18
Selecting the operating mode ........................................................... 19
Direct mode.................................................................................................................. 19
Half-bridge mode with dead time.................................................................................... 20
Practical Part 1: the input side .......................................................... 22
Pin GND...................................................................................................................... 22
Pin VDC (voltage supply DC/DC converter) ..................................................................... 22
Pin VDD (voltage supply electronics input side) ................................................................. 22
Pin VL / Reset (define logic level/acknowledge error) ....................................................... 23
Pin MOD (mode selection) ............................................................................................. 24
Pin InA (signal input A) .................................................................................................. 25
Pin InB (signal input B) ................................................................................................... 25
Pin SOx (status outputs).................................................................................................. 25
Pin RCx (RC networks for the dead times)......................................................................... 26
Practical Part 2: the power side........................................................ 27
Pin Gx (gate terminal).................................................................................................... 27
Pin Ex (emitter terminal) ................................................................................................. 28
Pin Cx (collector sense) .................................................................................................. 28
Pin Rthx (reference resistor)............................................................................................. 29
Layout and wiring ......................................................................................................... 30
The really fast variant: evaluation boards ........................................ 31
If you need any help, simply call our technical support ..................... 31
Important information: the SCALE driver data sheets......................... 32
Quite special: customized SCALE drivers............................................ 32
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Description and Application Manual
SCALE driver application – it’s never been so simple
As soon as you’ve read the following eleven and a half pages, you’ll
be able to use a SCALE driver.
Power electronics really has become that easy!
And you will learn directly from each paragraph where to access all
the details you need to obtain more detailed information. For you will
certainly want to know more about some of the topics covered.
Everything is described in full detail in the section “How exactly do
they work? The SCALE drivers in detail" from page 11 onwards, so
that you can find all the information that you need.
At the end of the brief introduction you will see from an example
how easily a current inverter can be put together with a SCALE driver.
A brief introduction
Mode selection and dead times
First of all select the mode in which you wish to operate the SCALE driver. There are
two modes: direct mode and half-bridge mode.
In direct mode, there are no links between the individual channels of a multiple driver.
And that’s how it works: the MOD input is connected to VCC and the inputs RC1
through RCn (depending on how many channels the driver has) are connected to
GND. In half-bridge mode, the chip set can directly generate the required dead times.
For half-bridge operation, the MOD input is connected to GND and an RC network is
connected to inputs RC1 through RCn for each channel to generate the dead time.
See page 26 for the dimensioning of the RC networks.
Voltage supply and logic level
The GND terminals (some SCALE drivers have several GND and several voltage
supply terminals) are connected to the ground terminal of the voltage supply unit. The
VDD and VDC terminals should be connected to a stabilized 15V supply source.
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The VL/Reset pin is used to define the logic level and to erase the error memory. The
circuits for 5V and 15V logic levels are shown in Fig. 11. There’s more on this topic
from page 23 onwards.
Signal inputs and status outputs
The PWM signals of the control electronics are applied to inputs A and B. Depending
on the selected mode, these inputs have a different function: in direct mode, input A is
assigned directly to channel 1, whereas input B controls channel 2.
In half-bridge mode, the PWM signal is applied to input A whereas input B carries the
release signal for both channels. There’s more on this topic on page 25.
The status outputs are “open collector” outputs and can thus be simply matched to all
logic levels and families. The outputs lead simply to the logic and are connected to the
logic supply via a pull-up resistor. There’s more on this topic on page 25.
Connecting the IGBTs
The auxiliary emitter (emitter control terminal) is connected to output “Ex” (where “x”
stands for the number of the drive channel in multi-channel drivers). In the same way,
the gate is connected to output “Gx”; but via a gate resistor or a gate resistor
network. There’s more on this topic from page 27 onwards.
The collector sense terminal “Cx” is connected via a diode to the collector of the IGBT.
On this point, read the hints from page 28 onwards and any additional hints in the
data sheet of the SCALE driver used.
Defining the turn-off threshold
The turn-off threshold and the response time are defined by a resistor connected
between the terminal “Rthx” and the emitter terminal “Ex”. An explanation of these
terms is found from page 17 onwards. A table or a diagram of the turn-off threshold
and the response time can be obtained from the data sheet of the relevant SCALE
driver.
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Description and Application Manual
Application example: 30kW inverter with six-pack driver
The drawing in Fig. 1 shows all the required components of the current inverter circuit.
The circuit diagram clearly illustrates the level of integration of the driver solution and
its simplicity in application.
U
V
W
DC(+)
eupec
21A
BSM100GD120DN2
15C
15B
15A
17C
17B
17A
19C
19B
19A
18C
18B
18A
16C
16B
16A
Not connected
13A
21B
13B
21C
13C
+
+
12
11
DC(-)
36
35
38
37
42
Rth1
RG1
10
9
41
44
43
Rth2
RG2
DC(+)
7
8
48
47
50
49
Rth3
RG3
6
54
53
56
55
60
Rth4
RG4
DC(+)
RG5
59
62
61
66
65
Rth5
RG6
DC(+)
Rth6
68
67
5
14C
4
14B
20C
3
14A
20B
2
20A
1
DC(-)
DC(+)
+15V
5
6
17
18
29
30
2
9
14
21
26
33
Input 6
Input 5
Input 4
Input 3
Input 2
Input 1
Status
4V7
GND
8
20
32
1
4
7
10
11
16
19
22
23
28
31
34
+15V
2k2
3
12
13
15
24
25
27
CONCEPT 6SD106E Six-pack driver
GND
Fig. 1 Complete circuit diagram of the 30kW inverter
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The circuit diagram in Fig. 1 shows all the components required for the inverter circuit.
The diagram thus illustrates clearly the level of integration of the driver solution and its
simplicity of application.
Compared with IPM solutions, which require more external components but offer no
additional flexibility in the selection of the switching properties, the SCALE driver
solution has the advantage of allowing the switching characteristic to be defined in
any way required with the few components that are still located externally. In
addition, the level of the protection cut-out (Vce monitoring circuit) can be freely
selected.
For this example, we assume that the drive controller already generates the dead
times internally. It thus supplies six drive signals. The controller operates with TTL
levels, so that we set the input VL (pins 8, 20, 32) to 4.7V. The PWM inputs are
marked with “Input 1”...”Input 6”.
However, the controller still has only one error input: so we must combine our six
status acknowledgements into a single signal “status".
The other inputs and outputs are now quickly connected in the correct way in
accordance with the description given on the preceding pages: the result is the
completed circuit diagram shown in Fig. 1.
And now you can switch on...
What is a “SCALE” driver?
"SCALE" stands for Scaleable, Compact, All-purpose, Low-cost and Easy-to-use.
This is a concise enumeration of the most outstanding properties of SCALE drivers.
Scaleable
One of the most important properties of the SCALE driver chip set is its scaleability. In
this context, the term scaleable means that the chip set — in contrast to all previous
approaches to integrated drive circuits — can be used for a very large range of
applications. The SCALE driver chip set can be used to implement solutions for diverse
drive currents (gate currents) and various drive powers. SCALE drivers are well suited
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Description and Application Manual
for almost any switching frequency, any modulation mode and not least for isolation
voltages of practically any magnitude.
SCALE drivers can be used to construct power sections from the kilowatt to the
megawatt range.
Compact
SCALE drivers accommodate all the necessary components on a minimum surface
area. They cover the following functions: driving, monitoring, status
acknowledgement, isolated voltage supply (DC/DC converters) and electrical isolation
of all signals between the control electronics and the power section.
SCALE drivers are currently the most compact driver solutions on the market with this
range of functions.
All purpose
The SCALE driver chip set offers maximum flexibility of operation: by switching the
mode accordingly, a choice can be made between half-bridge or direct-mode
operation.
In half-bridge operation, the chip set can generate the required dead times directly. In
direct mode, there are no links between the individual channels of a multiple driver.
Low cost
SCALE drivers are high-quality driver circuits for IGBTs and power MOSFETs with an
outstanding price/performance ratio. A SCALE driver contains all the components that
can possibly be integrated. It encompasses the driver function itself, plus monitoring,
acknowledgement, power supply (DC/DC converter) and electrical isolation of all
signals.
SCALE drivers are the most inexpensive drivers on the market offering this
performance.
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Easy to use
The interface to the electronics is very simple: the SCALE driver chip set can handle all
standard logic levels between 5V and 15V. The inputs have a Schmitt trigger
characteristic and make no special demands on the input signals. The status
acknowledgements are designed as open-collector outputs and are thus compatible
with all the usual logic levels.
Application is extremely simple because a SCALE driver contains all the functions of
an intelligent driver, and the drive signals, the status acknowledgement and the power
supply are completely isolated from the power section.
Application of SCALE drivers with standard IGBT modules is in most cases simpler
than an IPM, but without any loss in flexibility.
Your benefit:
the application advantages of SCALE drivers
Reliable operation
Gate driving with a bipolar control voltage (typically ±15V) allows the reliable
operation of IGBT modules of any size from any manufacturer. Thanks to the high
interference immunity attained by using a negative gate voltage, a number of power
MOSFET or IGBT modules can be connected in parallel.
Genuine electrical isolation
SCALE drivers contain miniaturized transformers for the isolation of all channels.
These offer outstanding isolation properties and low coupling capacitances.
The SCALE driver can be used to obtain isolation voltages of practically any
magnitude. The product-specific isolation data relating to the individual versions can
be found in the data sheets dealing with the individual types.
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Description and Application Manual
Reliable transformer principle
Pulse transformers were selected because they offer the following advantages over all
other designs: minimum delay times, no degradation effects, maximum service life
and the ability to obtain isolation voltages of any desired magnitude.
The MTBF (failure probability) of a pulse transformer of the kind used in the SCALE
drivers is better by a factor of 20 than that of a high-quality optical coupler, for
instance, and about 200 times better than that of a good fiber-optic link.
The extremely high interference immunity of at least 100kV per microsecond
predestines the SCALE driver to applications in which large potential differences and
large potential jumps occur between the power section and the control electronics.
Delay times
The delay times through the complete driver circuit are around 300...350ns. The
delays for the positive and the negative edges are symmetrical.
There are almost no differences in delay time between the different drivers, an
important factor for ensuring operation without offset problems as well as for parallel
circuits. Signal transfer is practically jitter-free.
Status acknowledgements
The pulse transformer is operated bi-directionally - for transferring both the drive
information and the status acknowledgement.
Ideal layout of the terminals
The terminal pins of the drivers are arranged so that the layout can be kept very
simple and the logic signal flow (input signal ⇒ drive circuit ⇒ power transistors) is
maintained.
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How exactly do they work? The SCALE drivers in detail
Overview
SCALE drivers are available in various versions in order to satisfy the different
requirements in terms of driver performance, number of drive channels, isolation
requirements and to cover the diversity of applications and standards.
The information given in this description is identical or practically so for all versions.
The product-specific data relating to the individual versions can be found in the data
sheets dealing with the individual types.
The concept of the SCALE driver circuit
The interface to the control electronics forms the first building block of the SCALE chip
set: the LDI (LDI = Logic to Driver Interface). An LDI drives two channels. The PWM
signals applied to inputs A and B are processed so that the drive information can be
fed to a pulse transformer for each channel.
The pulse transformers are responsible for the electrical separation of the drive
information. At the same time, they are also used in the reverse direction in order to
return the status information of each channel to the LDI.
The second building block of the SCALE driver chip set is used once for each drive
channel. This is the IGD (IGD = Intelligent Gate Driver). It receives the pulse-coded
information from the transformers and reconstructs the original PWM signal from it.
This is then amplified, making a gate current of several amps available to drive the
power semiconductor. Furthermore, the IGD contains protection functions that
safeguard the power semiconductor from harmful operating conditions.
The DC/DC converter makes the electrically separated power supply available to the
individual driver channels. The SCALE drivers require a simple stabilized 15V DC
supply.
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Block diagram of the “Logic-to-Driver-Interface” LDI 001
Rth
IGD
VDD
Rg
Viso1
LDI
Rth
GND
IGD
Rg
Viso2
VDC
Viso1
PWM
oscillator
Viso2
GND
Interface on
Electronic Level
Electrical
Isolation
Driver on
Power Level
Power
Semiconductor
(external)
SCALE Driver Module
Fig. 2 Block diagram of a two-channel SCALE driver
The block diagram shows a two-channel driver based on the SCALE chip set. For a
three-phase version, there is only one PWM oscillator, all other components are
present in triplicate.
For each channel, the SCALE drivers contain the electrical separation between the
control and power sides, an over-current and short-circuit protection circuit for the
power transistors, a feed monitoring circuit, a status acknowledgement circuit as well
as an electrically separated power supply for the drive electronics via an integrated
DC/DC converter.
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The power supply: the integrated DC/DC converter
All standard SCALE drivers contain a DC/DC converter. This is used for the power
supply of the individual driver channels. The electrical separation of the DC/DC
converters allows the SCALE drivers to be supplied from the electronic power unit
which is in most cases present in any case.
Drive energies of different magnitudes are required depending on the application –
and especially on the clock frequency and gate charge of the used power
semiconductors. SCALE drivers are therefore offered with differently dimensioned
DC/DC converters. The exact data of the relevant DC/DC converter can be obtained
from the data sheets of the individual SCALE drivers.
The electronic interface: LDI 001
PWM signals of the kind generated by the control electronics cannot simply be
transferred via transformers. This is particularly difficult when a large frequency range
and various duty cycle ratios are to be transmitted.
The LDI 001 logic-to-driver interface was developed for this reason. This IC has the
following main functions:
1)
Creation of a simple interface for the user. Both signal inputs have a Schmitt
trigger characteristic
2)
Simple matching to the logic level used in the electronics (5V...15V)
3)
Forming the dead times in a half bridge, where required. This function can also
be deactivated
4)
Coding of the PWM signals so that they can be transmitted via a pulse
transformer
5)
Evaluation of the status acknowledgement transmitted in coded form and its
subsequent buffering so that a quasi-static acknowledgement signal is available
to the user
A SCALE driver can be connected directly and with no additional components to any
logic circuit. In the same way, however, driving is also possible via longer cables:
with a 15V level, acceptable signal-to-noise ratios are obtained in such applications.
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The possibility of generating the dead times directly with the SCALE driver obviates
the external circuits that are usually required.
These functions make SCALE drivers directly compatible with practically all available
interfaces and levels. As a rule, therefore, the interfaces usually required for other
driver solutions are obviated.
Block diagram of the “Logic-to-Driver-Interface“ LDI 001
RC1
RC2
3
6
Mode Selector
7
V+
Channel 2
VCC 13
VL
GND 12
Pulse
Stop
Reset
Transformer
Channel 2
11
Logic
9
VL 2
Input A 4
Hi
Dual
Mode
Dead-
Logic
Time
Trafo
Interface
Error
Logic
Error
Lo
Reset
Channel 1
Input A
Input B 5
Input B / Enable
Pulse
Transformer
Channel 1
16
Logic
14
Status 2 8
Error Channel 2
Status 1 1
Error Channel 1
CONCEPT LDI 001
Trafo
Interface
Error
Logic
Error
Reset
Fig. 3 Block diagram of the LDI 001
All necessary functions of an intelligent gate driver are integrated in the IGD 001: the
transformer interface, overload and short-circuit protection, blocking time logic, status
acknowledgement, monitoring of the supply voltage and the output stage.
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The Intelligent Gate Driver: IGD 001
All necessary functions of an intelligent gate driver are integrated in the IGD 001: the
transformer interface, overload and short-circuit protection, blocking time logic, status
acknowledgement, monitoring of the supply voltage and the output stage.
An IGD 001 intelligent gate driver is used for each drive channel. This IC has the
following functions:
1)
Decoding the PWM signals transferred via the pulse transformer
2)
Amplifying the PWM signals to drive the final stage
3)
Power Semiconductor desaturation monitoring (short circuit & overcurrent
protection)
4)
Under-voltage monitoring
5)
Generating response and blocking times
6)
Status acknowledgement to the controller (LDI 001)
All necessary protection functions that safeguard the semiconductor from over-current
and short circuit are present locally in every driver (and thus every power
semiconductor).
In the same way, the local under-voltage monitoring circuit ensures for each channel
that the driver is released only when the supply voltage is sufficiently high. This
reliably avoids the critical condition of “half” driving of power semiconductors.
Every time an error is detected, a blocking time is applied locally on the driver. In
particular after a short circuit, power semiconductors require a “pause” in order to
cool down again before the next drive pulse is released.
The status (error or normal) can be queried at any time from the pre-connected
LDI 001.
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Block diagram of the ”Intelligent Gate Driver“ IGD 001
V+
V+
Vce Monitoring
13
V+
V+
V+
Viso
12
Transformer
Interface
Rref
3
1
Pulse
Flip-Flop
Rm
4
2
Cx
Dm
Ca
Error
8
Pulse Logic
5WK[
SO
Error
Reset
Uce Fail
Timer
Cb
5
7
Gx
V+
V+
Vcc Fail
RGx
15
Rthx
6
10
Power Supply
Supervisor
Ex
CONCEPT IGD 001
SCALE Driver Module
Fig. 4 Block diagram of IGD 001 intelligent gate driver with external wiring
All the functions shown in the inner block of Fig. 4 are integrated on the chip. The
components shown in the outer block are contained in the SCALE driver modules. This
means that practically no external components are required.
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Absolute safety: the protection concept
Short circuit and over-current protection
Every channel of a SCALE driver is equipped with a Vce monitoring circuit. A resistor
(Rth in Fig. 4) is used as the reference element for defining the turn-off threshold.
During the response time, the Vce monitoring circuit is inactive. The response time is
the time that elapses after turn-on of the power semiconductor until the transistor is
saturated.
Driver
Input
Voltage
+VL
0V
The characteristic described below is
shown graphically in Fig. 6.
After a Vce or under-voltage error, the
blocking time is initiated. During this
period, the driver blocks the power
semiconductor and accepts no drive
+15V
IGBT
signals. The blocking time is a function
Gate
0V
that runs locally on every driver
Voltage -15V
channel and is implemented within the
IGD 001. It starts immediately after the
+Vdc
threshold of the VCE monitoring circuit
set (with reference resistor Rth) has
IGBT
been exceeded. With the consequent
Collector
edge change of the drive signal, the
Vth
Voltage
“error” information is transferred for
0V
storage to the LDI 001, whose status
output SOx for the corresponding
Response time
channel now becomes active (Lo level).
The driver then ignores any drive
Fig. 5 Turn-on characteristic of an IGBT
signals that may be subsequently
applied until the blocking time has
elapsed. If no further drive signals are applied, the error information continues to be
stored in the LDI 001 even after the blocking time. The error memories can be erased
by briefly pulling the input VL/Reset to GND. However, these memories are also
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Description and Application Manual
erased automatically at the next edge change of the drive signal following the elapse
of the blocking time. The latter way of deleting the error memories is shown in Fig. 6.
The values of response and blocking times can be obtained from the data sheet of the
SCALE driver.
+VL
Input voltage
0V
+15V
Gate voltage
-15V
Overcurrent turn-off threshold
Load current
0A
Blocking time
(IGD 001)
Status output
(LDI 001)
0V
Blocking time (typically 1s)
t0
t 0 = Power-transistor turn-off in case of overcurrent
t1
t 0 - t 1 = Blocking time (all input signals are ignored)
Fig. 6 Short circuit & overcurrent protection / Function of the blocking time
Power supply monitoring
An under-voltage monitoring circuit blocks the driver if the supply voltage drops to
below about 10…11V. In the case of under-voltage, the power semiconductor is
driven with a negative gate voltage and an error is reported.
The monitoring is performed locally on each gate driver (integrated in the IGD 001).
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Selecting the operating mode
Direct mode
In direct mode, there is no locking between the various drive channels. This allows the
use of regulators that already generate a dead time, for example. However, several
channels may also switch on concurrently, as is shown in the following example of an
asymmetrical half bridge.
+ DC Link
+VCC
Channel 2
+VCC
C2
VCC (LDI)
Rth
MOD
1k
IGD
Reset
VL/Reset
PWM Input (15V Level)
+VCC +VCC
15k
InB
E2
LDI
15k
Channel 1
C1
SO2
SO1
Rg
G2
InA
SO2
Rth2
Rth
SO1
RC1
IGD
RC2
GND
GND
Rth1
Rg
G1
E1
SCALE Driver Module
- DC Link
Fig. 7 Application example for direct mode: An asymmetrical half bridge
Legend to Fig. 7
Both channels are always driven simultaneously. For this reason, InA and InB are also
connected together. The input VL/Reset is connected to VCC via a pull-up resistor.
Inputs InA and InB are then programmed for a 15V level.
The MOD input is on VCC, so that direct mode is selected. RC1 and RC2 are
connected to GND. This is necessary in direct mode.
Both status outputs SO1 and SO2 are run back separately. In this way, the control
electronics can detect which channel shows an error status in any given case.
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+15V
PWM Input
0V
+15V
Gate G2
-15V
+15V
Gate G1
-15V
Fig. 8 Signals curves of the circuit as per Fig. 7
Half-bridge mode with dead time
In half-bridge mode, two channels are always operated as a half bridge. In this
mode, the SCALE driver can generate the required dead times directly in a range
from about 100ns up to several microseconds. Only two external RC networks are
required (see page 26 for dimensioning). All power semiconductors can be turned off
by switching the release input (InB) to low.
+VCC
+ DC Link
Channel 2
4k7
C2
VCC (LDI)
4V7
Rth
MOD
IGD
GND
Reset
VL/Reset
Enable (TTL)
Rth2
Rg
G2
InB
PWM Input (TTL)
E2
InA
Inductive load
+VCC
LDI
15k
10k
10k
SO
Channel 1
C1
SO2
Rth
SO1
RC1
IGD
GND
GND
E1
100p
GND
GND
Rg
G1
RC2
100p
Rth1
SCALE Driver Module
- DC Link
Fig. 9 Application example for half-bridge mode with dead time generation
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Description and Application Manual
Legend to Fig. 9
The power section represents the typical half-bridge circuit of a voltage link-circuit
inverter. Both IGBTs must never be driven simultaneously in this application.
Input MOD is on GND, which means that half-bridge mode has been selected.
Input InA is the PWM input, InB is the release input.
With the 4V7 zener diode at the VL/Reset input, the Schmitt triggers of inputs InA and
InB are programmed for TTL level.
The two status outputs SO1 and SO2 are connected together: there is a common error
acknowledgement for both drive channels.
RC1 and RC2 are each connected to an RC network 10kΩ/100 pF. This results in
dead times of about 500ns.
The circuit characteristics are shown in Fig. 10
PWM Input +5V
(InA)
0V
Enable
(InB)
+5V
0V
+15V
Both channels go in OFF condition
Gate G2
-15V
+15V
Gate G1
-15V
Dead-Time (both channels OFF)
Fig. 10 Signals curves of the circuit as per Fig. 9
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Description and Application Manual
Practical Part 1: the input side
The following terminal pins are normally led to the outside in the SCALE drivers:
Label
Description
GND
Power supply GND
VDC
Power supply +15V terminal for the DC/DC converter
VDD
Power supply +15V terminal for the interface electronic (LDI 001)
VL/Reset
Define logic level/acknowledge error
MOD
Mode selection input
InA
Input A, PWM 1 / PWM
InB
Input B, PMW 2 / Enable
SO1
Status output channel 1
SO2
Status output channel 2
RC1
RC networks for dead time channel 1
RC2
RC networks for dead time channel 2
Pin GND
Pin GND is connected to the ground of the electronic power supply. If several GNDs
are present, all GNDs should be connected to ground.
Pin VDC (voltage supply DC/DC converter)
A stabilized voltage supply of +15V with respect to GND is connected to terminal
VDC. This input supplies the internal DC/DC converter(s). The current consumption
and other data can be obtained from the data sheet of the relevant driver. It is
recommended that a blocking capacitor is inserted between VDC and GND.
Pin VDD (voltage supply electronics input side)
A stabilized voltage supply of +15V with respect to GND is connected to terminal
VDD. Additional data may be obtained from the data sheet of the relevant driver.
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Pin VL / Reset (define logic level/acknowledge error)
This terminal is used for programming the switching thresholds of Schmitt trigger
inputs InA and InB. These inputs switch on at 2/3 of the voltage applied to VL. A level
of 1/3 of this voltage acts as a turn-off signal.
+15V
+15V
R1
4k7
(optional)
1 = Reset
GND
VL/Reset
D1
4V7
Q1
R1
1k
GND
(optional)
VL/Reset
1 = Reset
Q1
GND
Fig. 11 Circuit for input VL/Reset for 5V logic (left) and 15V logic level
When the PWM signals have TTL level, pin VL is connected as shown in Fig. 11 (left).
When the signals at inputs InA and InB have 15V level, then pin VL should be
connected via a resistor of about 1kΩ to +15V (see Fig. 11 (right)). The switching
thresholds of Schmitt trigger inputs InA and InB are then 5V and 10V respectively. This
variant is recommended especially in the case of longer connecting cables between
the control electronics and the driver; this produces higher signal-to-noise ratios.
In addition, the input VL has a double function: if it is pulled to GND (see Transistor
Q1 in Fig. 11), the error memories of the LDI 001 are erased when they were
previously set.
The current consumption of the inputs VL is (depending on the switching status and per
LDI 001):
typ. 0.14...0.5mA @ 5V
typ. 0.4...1.4 mA @ 15V
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Description and Application Manual
Note:
When a SCALE driver is turned on, the error memories are usually set. They can be
erased by pulling pin VL to GND after turn-on or during the entire turn-on process (for
example by a power-up reset signal). However, the error memories are also erased
automatically at the first edge of a drive signal after the blocking time has elapsed
(see also Fig. 6).
Important notes:
The VL/Reset input has no Schmitt trigger characteristic like signal inputs InA and InB.
For this reason, only “clean” digital levels are permissible. Voltages smaller than 1V
are regarded as a reliable level indicator for the error reset function. Voltages
between 4V and 15V are regarded as safe logic levels. Levels between 1V and 4V
must be avoided.
Pin MOD (mode selection)
The input mode selection “MOD” can be used to select the operating mode of the
LDI 001.
If the MOD pin is connected to GND, half-bridge mode is selected. In this operating
mode, inputs RC1 and RC2 must be connected to RC networks. For the dimensioning,
see Section “Pin RCx (RC networks for the dead times)” from page 26 onwards.
In half-bridge mode, inputs InA and InB have the following functions: InA is the PWM
input and InB has the release function.
If the level on InB is “Lo”, then both channels are blocked. With a Hi level on InB, the
outputs are released, depending on InA. In the event of an edge change from Lo to Hi
at InA, channel 1 switches off immediately and channel 2 switches on when the dead
time has elapsed. In the event of an edge change from Hi to Lo at InA, channel 2 is
immediately switched off and channel 1 is switched on when the dead time has
elapsed. The characteristic is shown in Fig. 10.
If the MOD pin is connected to VCC, direct mode is selected. In this operating mode,
there is no mutual influence between the two drive channels. InA affects channel 1
and InB affects channel 2. In each case, a high level at the input leads to switch-on of
the corresponding IGBT. This operating mode should be selected when the control
electronics has already generated the dead times and a control signal is thus present
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Description and Application Manual
for each power semiconductor. Moreover, in this operating mode both channels can
also be driven either simultaneously or in overlapping mode.
Note:
In direct mode, the two pins RC1 and RC2 are connected to GND. If this is not done,
unexpected switching processes will result.
Pin InA (signal input A)
In direct mode, terminal InA drives channel 1 directly. The input has a Schmitt trigger
characteristic and corresponds to positive logic: a Hi level switches the power
semiconductor on, a Lo level means a switch-off state.
In half-bridge mode, the PWM signal for the phase branch is connected to InA (see
also “Pin MOD” from page 24 onwards).
Inputs InA and InB can be operated with 5V...15V levels (see also “Pin VL/Reset”
from page 23 onwards).
During the build-up of the supply voltage, both inputs InA and InB or input VL/Reset
should be on GND, so that no uncontrolled drive signals are generated.
Pin InB (signal input B)
In direct mode, terminal InB controls channel 2 directly. The input has a Schmitt
trigger characteristic and corresponds to positive logic (like InA).
In half-bridge mode, the release signal for the phase branch is connected to InB. Hi
level means release, Lo level means that all channels are blocked (see also “Pin
MOD” from page 24 onwards).
Pin SOx (status outputs)
The “x” in “SOx” stands for the number of the drive channel in multi-channel drivers.
The output stage SOx consists of an open-collector transistor (see Fig. 3). The output is
pulled to GND if an error has been detected in channel x. The transistor goes high
when no error is present.
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Any number of status outputs can be connected together directly if a common error
signal is required for each phase or current inverter (see the examples in Fig. 1 and
Fig. 9).
The status outputs can be pulled to +5V...+15V via a pull-up resistor. A current of
1.5mA can be applied to the outputs SOx.
How the status information is determined
Every time that an edge of a drive signal changes:
a)
the error memory in the LDI 001 is erased (for each channel),
b)
the status information of the IGD 001 is transferred to the LDI 001,
c)
if an error was detected in the IGD 001 (and the blocking time is still running),
then the error memory in the LDI 001 is set (and the output is pulled to GND).
Note:
The error memory can also be erased when VL is pulled to GND (see “Pin VL”). The
error memory is then reset at the next edge change as long as there is still an error in
this channel.
Pin RCx (RC networks for the dead times)
The “x” in “RCx” stands for the number of the drive channel in multi-channel drivers
In half-bridge mode, an RC network is connected to each RCx terminal. It determines
the dead time of the corresponding channel.
Table for values of the dead times of RC networks:
R
C
typ. dead time
10k
47pF
£ 200ns
10k
100pF
£ 500ns
15k
120pF
£ 1.1ms
22k
150pF
£ 2.1ms
33k
220pF
£ 4.6ms
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These values produce the smallest scatter of dead times over the whole temperature
range. Resistance values below 5kΩ are not permissible.
The RC networks must be connected as shown in Fig. 9: the resistor is connected to
VCC, the capacitor to GND.
In direct mode, all RC inputs must be connected to GND.
Practical Part 2: the power side
In the SCALE drivers, the terminal pins described below are usually accessible from the
outside:
Pin Gx (gate terminal)
The “x” in “Gx” stands for the number of the drive channel in multi-channel drivers.
The output Gx is the output for the gate drive. When the SCALE driver is supplied with
15V, the gate is driven with ±15V. The negative gate voltage is generated internally.
A sufficiently low-resistance termination of the gate is ensured by the SCALE driver
even if it is not supplied with the operating voltage.
The maximum permissible gate current can be obtained from the data sheet of the
SCALE driver used. For the correct selection and calculation of drivers, reference is
made to Application Document AN-9701 from CONCEPT “IGBT drivers correctly
calculated”.
SCALE Driver
G
E
In order to allow the
switching speed to be set
independently during both
turn-on and turn-off, a gate
circuit can be used with two
gate resistors and a diode
(see Fig. 12).
Fig. 12 Asymmetrical gate resistors
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Pin Ex (emitter terminal)
The “x” in “Ex” stands for the number of the drive channels in multi-channel drivers.
This terminal should be connected to the emitter or source terminal of the power
transistor. The connection must be as short as possible and be run directly to the
emitter or source terminal of the power element. This terminal should be used in
modules with auxiliary emitters or an auxiliary source. This terminal is also used as the
low end of the reference resistor Rthx. Where possible, this should be connected
directly to the terminal Ex of the driver.
Pin Cx (collector sense)
The “x” in “Cx” stands for the number of the drive channels in multi-channel drivers.
This terminal is used to measure the voltage drop across the turned-on power transistor
in order to ensure protection from short circuit and overload. It should be noted that it
V+
1,4mA
V+
150uA
4
OVERCURRENT
Rm
Dm (2 x 1N4007)
Cx
Ca
5
5WK[
MEASURING
RGx
Gx
Rthx
IGD 001
Ex
SCALE Driver Module
Fig. 13 Principle of the collector sense circuit
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must never be connected directly to the drain or collector of the power transistor. A
circuit with a high-blocking diode (Dm) must be included to protect the measuring
terminal from the high drain or collector voltage of the turned-off power element. For
1200V and 1700V modules, a circuit made up of two or three diodes of type
1N4007 connected in series has proved its worth in place of exotic higher-blocking
elements (see Fig. 13). It is recommended that the voltage of these diodes be overdimensioned by at least 40%. Fast diodes are not required here. Standard line diodes
are quite sufficient.
A current source integrated in the IGD 001 ensures that a current flows through the
diode(s) in the power semiconductors when the power transistor is turned on. A
voltage is thus applied at the comparator that corresponds to the forward voltage of
the turned-on transistor plus the diode forward voltage and the voltage drop across
Rm (about 250 mV).
It should be noted that power transistors take a finite time to turn on, especially in the
case of IGBTs, that can take several microseconds to completely switch through. The
current source and the capacitor (Ca) cause a delay in the measurement after the
power transistor has been turned on. This delay is known as the response time. Its
magnitude as a function of the turn-off threshold can be obtained from the data sheet
of the selected SCALE driver.
Negative voltages are impermissible at the input Cx.
Pin Rthx (reference resistor)
The “x” in “Rthx” stands for the number of the drive channels in multi-channel drivers.
A resistor is connected to this pin as a reference. It defines the maximum voltage drop
across the turned-on power transistor at which the protection function of the drive
circuit is activated and thus the power transistor is turned off.
The protection function is always active when the voltage at Cx (measurement
drain/collector) exceeds the voltage at Rthx. Ex is the reference potential. The
reference resistor must be placed as close as possible to the driver module.
The current source in the SCALE driver supplies a current of 150µA.
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The reference resistor can be calculated as follows:
Rth =
Vth
150µA
Vth = turn-off threshold
Example: required turn-off threshold Vth = 5.85V
Rth =
Vth
5.85V
=
= 39kW
150µA
150 µA
Note:
Because of the voltage drops across the diode Dm (approx. 0.6 V per diode) and the
resistor Rm (approx. 250 mV) in the collector sense circuit, the voltage at the power
semiconductor – at which the protection function cuts in – is lower than the threshold
calculated above by about 850mV with a diode (or 1.45V if two diodes are
connected in series). In this example with two diodes connected in series, the
protection function thus reacts when the collector voltage exceeds a value of 4.4V
(5.85V-1.45V).
Layout and wiring
Drivers should as a rule be
placed as close as possible to
the power semiconductors so
that the leads from the driver to
the transistors are as short as
possible. Lead lengths of more
than 10 cm must be avoided.
When
the
power
semiconductors are connected
by stranded wires, it is
recommended always to twist
the three associated leads Gx,
Ex, and Cx (see Fig. 14).
It is also recommended to place
two
15V
zener
diodes
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SCALE Driver
C2
G2
15V
15V
15V
15V
E2
C1
twisted wires
max. 10cm
G1
E1
Power GND
Fig. 14 Wiring driver Ð IGBT
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connected in counter-series immediately between the gate and emitter of the IGBTs
(see Fig. 14). This prevents the gate voltage from increasing to an impermissible level
due to parasitic effects (such as the Miller effect). An excessive gate voltage increases
the short-circuit current to an over-proportional extent and can lead to destruction of
the power semiconductor.
The really fast variant: evaluation boards
CONCEPT offers a wide range of evaluation boards to introduce users quickly to the
sector of IGBT technology and to the protection concept used with SCALE drivers.
These boards represent completely built up and tested current-inverter circuits in the
power range from 10 kW to over 1000 kW and contain the power semiconductors
(IGBTs), a driver card with correctly matched drivers and the link-circuit capacitors.
The power sections are designed with very low inductance.
Together with the documentation supplied, these evaluation boards can be used to
create prototype equipment that is ready to use within a matter of hours. You are
invited to request an overview of the available evaluation boards.
If you need any help, simply call our technical support
CONCEPT offers you expert help for your questions and problems:
E-Mail: [email protected] or on the Internet: www.CT-CONCEPT.com
Fax international ++41 32 / 322 22 51 (in Switzerland: 032 / 322 22 51)
Tel international ++41 32 / 322 42 36 (in Switzerland: 032 / 322 42 36)
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Description and Application Manual
Important information: the SCALE driver data sheets
A data sheet is available for every SCALE driver.
Please request our overview of SCALE drivers.
Quite special: customized SCALE drivers
If you need a power MOSFET or IGBT driver that is not included in the delivery range,
don’t hesitate to contact CONCEPT or your CONCEPT sales partner.
CONCEPT engineers have more than 15 years experience in the development and
manufacture of intelligent drivers for power MOSFETs and IGBTs and have already
implemented a large number of customized solutions.
Exclusion Clause
CONCEPT reserves the right to make modifications to its technical data and product
specifications at any time without prior notice. The general terms and conditions of
delivery of CT-Concept Technology Ltd. apply.
Manufacturer
Your Distribution Partner
CT-Concept Technology Ltd.
Intelligent Power Electronics
Renferstrasse 15
CH-2504 Biel-Bienne
(Switzerland)
Phone ++41 - 32 - 341 41 01
Fax ++41 - 32 - 341 71 21
E-Mail [email protected]
Internet www.CT-CONCEPT.com
Internet www.IGBT-Driver.com
Copyright 1998, 1999 by CT-Concept Technology Ltd. - Switzerland.
We reserve the right to make any technical modifications without prior notice.
Page 32
All rights reserved.
Version from 26.05.99
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