Intertech, 42V Automotive Systems Conference, Chicago, September 17-18, 2001
Semiconductors in the 42V PowerNet
Dr. Alfons Graf, Infineon Technologies AG, Munich
INTRODUCTION
THE 42V POWERNET PERMITS NEW
APPROACHES
International bodies have been seriously discussing
the introduction of a 42V vehicle electrical system
(42V PowerNet) since 1995. This period has seen
euphoric and less euphoric phases when it came to
assessing the advantages and disadvantages of this
new PowerNet and the timing of its market introduction.
The main question repeatedly asked in all discussions
centering on the 42V PowerNet is “why?”.
Now that most major technical problems are known, I
regard it as an excellent achievement to have now
produced a workable and internationally agreed draft
specification. This will give system suppliers a degree
of development security.
Discussions conducted by individual automobile
manufacturers about the cost/benefit ratio were more
controversial than the technical details, leading to different scenarios for large-scale introduction depending
on their outcomes. For instance, it emerged quite
some time ago that the first starter generators with a
very simple 42V PowerNet would be going into volume production in 2002-2003, and that the first more
complex 42V/12V dual-voltage systems would be introduced onto the market starting in 2005 (Mercedes
S class). The first purebred 42V vehicles can be expected after about 2006-07.
- Lower currents
e.g. a factor of 3
- Reduction of power semiconductor costs
e.g. 20% chip size
- Cable cross section reduction
e.g. 12kg to 6kg mass
- Efficiency increase
Alternator, distribution, switching
e.g. from 40% to 85%
- Cost reduction due to new specifications
Overvoltage, reverse battery
load-dump, jump-start,
e.g. -12V to -2V
- New power application can be realized
e.g. EVT, Mild Hybrid
- Enables reduction of fuel and emission
e.g. start/sop, recup.
- Enables electrification of accessory drives e.g. hydraulic pumps
Fig. 1: Advantages from using the new 42V PowerNet
Fig. 1 shows some of the reasons for using 42V.
Firstly, currents are reduced by a factor of three due to
the higher voltage. This allows power semiconductors
to be reduced to, for instance, 20% of the original chip
2)
size and average cable sets to be made about 6 kg
4)
lighter . Changing the voltage also makes it possible
to significantly increase the efficiency of generating,
distributing, and switching electric power. Where the
generator is concerned, it should be possible to raise
the efficiency level from today’s modest 40% to perhaps 85%.
Against this background, a Toyota announcement in
June 2001 came as something of a surprise. It said it
would be launching a simple hybrid vehicle (THS-M
1)
Toyota Hybrid System-Mild)
onto the market as
early as 2001. It would be equipped with a belt-driven
42V starter generator and allow braking energy to be
recovered in lead-acid batteries.
Another very important reason is that the smaller currents are what will make new power applications such
as electromagnetic valve operation (EVT) or so-called
mild hybrid systems with a starter generator possible
and affordable. Under these conditions a start/stop
function for the IC engine, low-emission engine
startup, and recovery of braking energy will then provide an optimum basis for achieving an average reduction in emissions and gasoline consumption. This
energy and gasoline saving effect can be further extended by consistently electrifying what are currently
mechanical or hydro-mechanical ancillary units in
combination with suitable controls.
It is clear, despite the modest scope of this 42V PowerNet, that the general introduction and spread of the
42V PowerNet can be held back no longer; it will even
make surprisingly fast headway here and there, even
if the aimed-for solution variants will then appear surprisingly simple and pragmatic.
1
gradual 25% reduction in average CO2 emissions in
new vehicles to 140g/km by the year 2008 from a figure of 186g/km in 1995. An average value of 169g/km
was attained in 2000 according to the ACEA, chiefly
through measures such as direct injection for diesel
and gasoline engines. 120g/km is being further targeted for the year 2012. Experts agree that future reductions can only be achieved through drastic measures such as electrification and consistently changing
over high-power ancillary units to 42V. Similar pressure is being generated in the USA through CAFE
(Corporate Average Fuel Economy), a fuel-saving
program launched back in 1975. This today specifies
an average gasoline consumption level of 27.5 mpg
(miles per gallon) for new passenger cars and 20.7
mpg for new off-road vehicles and what are called
SUVs (Sport Utility Vehicles).
It is widely known that a saving in power and hence
gasoline can be achieved by providing power to match
demand and employing electrically-powered steering
(EPS). Similar arguments apply to the air-conditioning
compressor, ABS system, fuel pump, and water
pump. Other ideas going even further seek to achieve
an up to 5% fuel saving by means of an IC engine operated at thermal optimum. The key to success for an
engine operated at thermal optimum again lies in
electrified ancillary units such as air cooler and water
pump, but also in employing electrically operated
analog valves instead of the conventional cooling water thermostat. The 42V PowerNet will form the basis
of optimized thermal management.
Car Type
Standard
Mild Hybrid
Parallel Hybrid
Serial Hybrid
Energy
Fuel
Fuel
Fuel
Fuel, Propane
Engine
E-Motor
100kW
70kW
5kW
60kW
30kW
Drive
Engine
Engine
+ E-Boost
+ Recuperate
14V, 1kW
42V, 6kW
Today
Powernet:
E-Traction:
2010
Powernet:
E-Traction:
Fuel Cell
Electr. Car
Hydrogen,
Methanol, Fuel
Battery
40kW
80kW
80kW
80kW
Engine or/and
E-Traction
+ Recuperate
E-Traction
+ Recuperate
E-Traction
+ Recuperate
E-Traction
+ Recuperate
14V, 1kW
42V, 10kW
14V, 1kW
288V, 30kW
14V, 1kW
400V, 80kW
14V, 1kW
400V, 80kW
14V, 1kW
400V, 80kW
42V, 5kW
42V, 10kW
42V, 5kW
288V?, 30kW
42V, 5kW
400V, 80kW
42V, 5kW
400V, 80kW
42V, 5kW
400V, 80kW
Toyota, 2001
DaimlerCh. ‘05
Toyota Prius, ‘97
Honda Insight, ’98
Dodge Durango 03
DC Necar, 2004
Honda FCX, ’03
GM HydroGen1
Honda EV+
In my opinion the 14V operating voltage will disappear
from all types of vehicles over the long term. Only then
will it be possible to use identical parts and increase
the volume of individual components. I think there will
be a transitional period up to at least 2020 that will see
a steady decline in the percentage of 14V vehicles
and 14V components produced.
Fig. 2: Overview of different vehicle types and their
operating voltages now and in 2010
The same considerations apply to the 24V PowerNet
in the European heavy duty truck market and the 12V
PowerNet in the US heavy duty truck market. Over the
long term, starting around 2010, I think most newly
developed commercial vehicles will have a 42V PowerNet.
The 42V PowerNet is normally associated with conventional vehicles with an IC engine and starter generator; it is customary here to refer to mild hybrid or
soft hybrid vehicles (see Fig. 2). As the initial step, the
42V supply will be used in these vehicles for the
start/stop, boost, and braking energy recovery functions; the rest of the PowerNet will continue to operate
at 14V. In the long term, these and conventional vehicles will only be equipped with a 42V supply. Essential
requirements for this are 42V control units, for example for electromechanical steering and braking, electric fans, door and seat control units, and also lamp
modules, etc. On this assumption, use of the 42V
PowerNet will extend to other types of vehicles such
as parallel-hybrid, serial-hybrid, fuel-cell, and pure
electric vehicles, as basically the same convenience
and security functions need to be provided here, too.
But as power exceeding 30 kW is generally required
for electrical operation in these vehicles, a significantly
higher voltage, typically between 200V and 400V,
must be selected for this electric drive. The introduction of the 42V PowerNet will not alter that situation in
any way.
42V AND ITS IMPACT ON POWER
SEMICONDUCTORS
Power semiconductors require a much higher dielectric strength than given by 12V for use in today’s 12V
PowerNet. Protected power semiconductors generally
have an active zener clamp in the 45V to 60V range.
This active zener clamp must be between 60V and
70V for semiconductors for the 42V PowerNet
application
12V automotive el. power net
supply
VAZ
generator
>45/60V
generator
>60/70V
generator
>65V
DC/DC conv.
>80V
power switching
42V automotive el. power net
starter/generator, power switching
24V truck el. power net
power switching
80V e.g. local high voltage
fuel direct injection
Economizing on fuel and reducing harmful emissions
will be the main arguments for introducing 42V in vehicles: on the one hand they can be very clearly conveyed to end customers; on the other hand they are
becoming legal requirements in certain countries. For
example, under the umbrella of the ACEA organization (Association des Constructeurs Européens
d’Automobiles) the “environmental commitment” policy
of European Automobile manufacturers is calling for a
60-80V active zener clamp
--
>60/80V
fast inductance de-excitation
12/24/48V industry application
power supply
>65V
power switching
Fig. 3: Overview of the voltage categories of various
automobile and industrial applications
Fig. 3 shows this correlation alongside the zener voltages customary in other automobile and industrial ap2
pendent here not only on the nominal operating voltage but also on the dielectric strength in the presence
of possible overvoltages. A value of 30V has been
assumed for this overvoltage withstand capability in
Fig. 5.
This overview very clearly shows that the requirements for 42V semiconductors are an excellent match
for existing applications and that uniform requirements
can even be inferred here.
100
Conductance, Silicon Area [%]
Definition of 42V PowerNet:
-2V
100ms 0
reverse
polarity
Umin Ustart
18V 21V
min.
start voltage
(start profile)
Uop,min
30V
min. continuous
operating voltage
UN
42V
nominal
voltage
Ueff-max,statUmax,stat Umax,dyn
48V 50V 58V
max. continuous
operating voltage,
including ripple
max. dynamic
overvoltage
(load dump)
Definition of semiconductor requirements at 42V:
-2V
100ms 0
18V
42V
Vbb(on)
Vbb(AZ)
58V
75V*
2500
Conditions:
Pload = const.
Ploss = const.
Vmax = VN + 30V
90
80
2000
70
60
1500
50
40
1000
Resulting silicon area
30
Conductance ~1/VN²
Specific RON ~e
c(VN+30V)
20
500
10
0
0
reverse
polarity
min.
operating
voltage
nominal
operating voltage
* : Dependant on semiconductor technology and circuit concept
Specific RON [%]
plications. A 65V zener voltage is generally required
for industrial and 24V heavy duty truck applications; a
60V-80V zener voltage is often required and employed for fast inductance de-excitation.
max. zener
max. operating
clamp voltage
voltage
=
=
min. zener (avalanche) min. technology
clamp voltage (Vmax) breakdown voltage
20
40
60
80
100
120
0
140
Nominal Supply Voltage VN [V]
Fig. 5: Under the same conditions as for 14V, the 42V
PowerNet permits a drastic reduction in the chip area
of power transistors
Fig. 4: Voltage ranges of the 42V PowerNet and resulting voltage requirements for 42V power semiconductors
This means that the chip area reduces very dramatically as the operating voltage increases due to the
switch’s higher permissible conductance, then assuming a flatter, slowly rising characteristic. The necessary chip area for 42V in this regard is only around
20% compared to 14V.
Fig. 4 first shows the voltage levels as provided in current proposals for the DIN and ISO standard. Nominal
operation ranges from 30V to 48V. A generator ripple
with a max. peak value of 50V can be superimposed
on the effective upper bound of 48Vrms. A max. overvoltage value of 58V may additionally occur for max.
400 ms.
So if the conditions are constant, much smaller chip
areas are possible for power switches in the 42V
PowerNet. These smaller chip areas can also be
housed in smaller packages; see Fig. 6.
Voltage dips to 18V for 15 ms and to 21V for max. 20s
are described by a special start profile. A central reverse polarity protector limits the load for electronic
systems in the event of polarity reversal to –2V for
max. 100 ms (see also Figs. 17-19).
PROFET
14V
ST
20A
load
>
G
IN
Requirements for the power semiconductors in this
42V PowerNet can now be derived from this. As a favorable factor, intelligent power semiconductors have
a nominal operating range of 18V to 58V here. Protection functions for brief voltage peaks in the µs
range are consequently over 58V. To obtain these
characteristics, Infineon selects breakdown voltages
of 75V to 90V for the various semiconductor technologies (see also Fig. 9). In the event of polarity reversal,
a semiconductor device in a certain application should
withstand –2V for 100ms with no additional circuitry.
S
D
IS
TO218
PV=1.7W
2.9mΩ
RON=2.9m
Ω
280W
dramatic cost reduction:
chip area + package + mounting
PROFET
42V
S
D
IN
ST
6.5A
load
>
G
IS
D-PAK
PV=1.1W
18mΩ
RON=18m
Ω
280W
calculation at Tj=100°C
Fig. 6: Smaller chips can be housed in smaller packages, thus reducing the overall cost of power semiconductors
Shown here is a 14V/42V comparison between
switches for operating a load with 280W, for example
an electrically heated rear windscreen. At 14V this
function can be performed by a 2.9mΩ switch in a TO
218 package, whereas 18mΩ in a D-Pak is sufficient
at 42V, and with less power dissipation. The smaller
chip area with a smaller package, plus the reduced
power dissipation, naturally result in major cost benefits in this example.
It has already been mentioned that the smaller currents make it possible to reduce the size of the semiconductors employed and hence also their cost.
Fig. 5 shows the chip area of a power semiconductor
assuming that the power in the load and the power
dissipation in the switch remain constant if the operating voltage is variable. As is generally known, the
chip area is proportional to the conductance of the
semiconductor switch multiplied by its ON resistance
per unit area. This area-specific ON resistance is de3
of size and power dissipation as mentioned. There are
no changes to other subsystems such as the micro
controller and memory, which by contrast are supplied
with 5V or less.
System cost reduction in all cases
140%
100%
RO
PO
PV
Ch
ip
20%
mi
opti
cos
t
opt
im
zed
ize
d
14V
55V
RON=
RO
PV = 1/9 PO
Achip
PV
RON≅ 1.4 x RO
PV ≅ 0.16 x PO
Achip
PV
5V, 12V
12V
12V
System
RON= 9 x RO
Achip
PV = PO
PV
42V Nominal Voltage VN
75V Technology Breakdown Voltage
EPS
Power Stage
6x
Chip
Costs
D-Pak
42V:
IMotor = 30A
VBRDSS=75V
Ron=20mΩ
PV= 150W
5V
12V
I/O
12V
Digital and
Analog Circuit
5V...1V
µC,
ADC, DAC,
RAM, ROM,
Logic, PWM
VBRDSS=45V
Ron=4.5mΩ
PV= 300W
PV
Switch Mode Supply
42V to 5V...1V
Pv = 5-20%
5V
12V
I/O
42V
Sensor
Conditioning
5V...1V
I/O
42V
Digital and
Analog Circuit
5V...1V
5V
Power Switches
12V, IOUT =100%
Pv = 100%
Achip = 100%
5V...1V
5V, 12V
42V
System
12V
Bus Controller 5V...1V
Sensor
Conditioning
5V...1V
5V
12V
Bus Transceiver 12V
I/O
12V
42V
TO220
14V:
IMotor = 90A
Linear Supply
12V to 5V...1V
Pv = 100%
42V
42V
Bus Transceiver 42V
Bus Controller 5V...1V
µC,
ADC, DAC,
RAM, ROM,
Logic, PWM
Power Switches
42V , IOUT =33%
Pv = 20-100%
Achip = 100-20%
5V...1V
Fig. 8: Principal modifications to an electronic system
during transition from 12V to 42V
TO220
VBRDSS=75V
Ron=6.5mΩ
PV= 50W
Only these systems’ voltage supply has to be
changed. Linear voltage regulators are no longer possible on account of the high power dissipation.
Switching regulators to be used here offer the advantage of significantly reduced power dissipation in the
voltage regulator, but at the expense of higher complexity due to the necessary inductance and the filter
costs (see also Figs. 11 and 12). Moreover, all input/output channels in the overall system for sensor
connections and for transmission and communication
lines such as CAN and LIN must be designed to be
short-circuit-proof for 42V. This is technically feasible
and has a negligible impact on overall costs as only
the relevant output stages have to be adapted to the
higher voltage. The new communication chips could
then also be used for remaining 12V systems.
Fig. 7: The cost benefits due to the higher voltage can
be gained from reduced power semiconductor costs or
lower costs on account of the power dissipation: typical application - electromechanical power steering
EPS
These cost benefits are shown in greater detail in
Fig. 7. On the basis of 100% chip costs for 14V, a cost
benefit can be gained in the system in various ways.
By taking the route of chip cost optimization the chip
area can be reduced to around 20%; power dissipation in the switch remains unchanged, ON resistance
increases by a factor of 9. The cost benefit is gained
from reduced chip and package costs.
Technology
On the other hand, the chip area and hence the cost
of this can remain virtually unchanged. ON resistance
then only increases by a factor of 1.4, but power dissipation is reduced to 16%. A cost benefit is achieved
here through drastically reduced cooling requirements.
So a cost optimum is to be found more with reduced
chip costs or with reduced cooling measures, depending on the way of looking at the situation and the
particular application. This is shown by way of example for the power stages of an EPS (electromechanical
power steering) system. A solution at 14V with six
4.5mΩ chips in a TO220 package with a total power
dissipation of 300W can now be shown for 42V e.g.
either with six 6.5mΩ chips in a TO220 package with
50W power dissipation or with six 20mΩ chips in a DPak with 150W power dissipation.
SPT4/90
VBr > 90V
Product-family
Smart Power ICs
VAZ > 80V
S-SMART/80
VBr > 80V
Smart Power Switches
VAZ > 65V
OptiMOS/75
VBr > 75V
FET / TEMPFET
VBr > 75V
Concept
Monolithic / Chip-on-Chip
Normalized Chip Area
Basically there are two ways to get benefits:
✔ chip area optimized
✔ power dissipation optimized
Application
Gasoline Direct Injection
VNom = 70V / 42V /24V
Truck Applications
Time Schedule ES /
Products
9/98
9/00
6/00
TLE customized
TLE 6387 5V adj., 2A
TLE 6361 5+3.3+2.5V
Truck ABS / TRC / VDC
VNom = 42V / 24V
High Current Switches
7/01
9/99
9/98
1/01
10/98
open
BTS 4140N
1Ω
BSP 752R
200 mΩ
Ω
BTS 723
2* 95 mΩ
Ω
BTS 6163D
21 mΩ
Ω
BTS 660P
9 mΩ
Ω
BTS 6166
3.5 mΩ
Ω
Starter-Generator
VNom = 42V / 24V
High Speed PWM
DC / DC Converter
open
11/99
3/01
BTS 282Z-7
8.0 mΩ
Ω
SPP 80N08S2 6.8 mΩ
Ω
SIPC 42S2N08 4.2 mΩ
Ω
Fast Inductance De-excitation
Fig. 9: Selection of currently available power semiconductors for 42V and their technologies
Fig. 9 shows the technologies scheduled at Infineon
Technologies for use in the 42V PowerNet. MOSFETs
for use in starter generators or DC/DC converters are
implemented using OptiMOS technology with 75V
breakdown voltage. The performance and availability
of some products are shown in the right of the figure.
We can now look at a complete electrical system in
Fig. 8. It can be seen very neatly here in the case of
42V that, depending on the requirements, the output
stages can be adapted to suit different needs in terms
Intelligent power switches, on the other hand, are currently implemented using S-Smart technology with
80V breakdown voltage. Products employing this type
4
cant; its deactivation function will then be implemented
using the existing electric switch and a software function. This will mean a significant increase in potential
loads drawing quiescent current. Expressed straightforwardly, this means power semiconductors designed
for use connected to the 42V battery need to be optimized in terms of quiescent current. The same applies
to the voltage regulators. Infineon will be squaring up
to this challenge with a variety of technical solutions.
of technology have been used for more than 10 years
in 24V truck applications.
Finally, more complex functions can be implemented
using SPT4/90V BCD technology. Examples include
system ICs for gasoline direct injection, communication chips, and voltage regulators.
All the applications in the 42V PowerNet can be
shown with the aid of the three basic technologies
mentioned. For cost reasons, these technologies are
frequently combined in a single package in so-called
chip-on-chip components.
Source
16V
50V
Power Loss (linear regulator)
1.1W
9.5W
-
0.2W
‘30’
VI
I
470 nF
‘31’
Battery terminal designations
30 + 15 and 31
“30” and “31”
Battery size Wh
e.g.
800 Wh
800 Wh
Battery V, Ah
e.g.
12V, 66 Ah
36V, 22 Ah
Quiescent current per car
18 mA
6 mA
Quiescent current per module
300 µA
<100µA
As already mentioned, linear voltage regulators will
not be used much longer in the 42V PowerNet on account of the high power dissipation. In particular,
changing the logic voltage from 5V to, say, 2.5V will
further intensify this problem. For example, the power
dissipation of a 2.5V, 200mA linear voltage regulator
at an input voltage of 50V would be 9.5W, see Fig. 11.
Switched voltage regulators perform this function with
a power dissipation of, for example, only 200mW, far
lower than at present with a 12V supply. This very low
power dissipation opens new possibilities for integrating voltage regulators in integrated system chips.
42V System
31
<300µA
Step down converter Quiescent current
is a must!
is a challenge!
Fig. 11: A switch-mode voltage supply has to be used
in the case of a 42V supply
Battery
15
max. Input Voltage
At 42V:
A quiescent current of, for example, 18mA, is today
allowed for the entire vehicle in the case of 12V; this is
approx. 300µA for each electronic module.
30
2.5V, 200mA
500mW
total Quiescent Current
Assuming a same-size battery with constant energy
for both 14V and 42V, a 66 Ah battery is used in the
case of 12V, for instance, and for 36V the one used is
correspondingly a 22 Ah battery.
Ignition
5V, 100mA
500mW
e.g.
Power Loss (switched regulator)
In 12V systems, quiescent current requirements for
vehicles with their engines switched off play a major
role in terms of ensuring a battery’s startup ability over
a period of several weeks. In future 42V systems the
quiescent current problem will be exacerbated for two
reasons, see Fig. 10.
12V System
42V
System Voltage/Current
Output Power
QUIESCENT CURRENT REQUIREMENTS,
VOLTAGE SUPPLY, AND COMMUNICATION IN THE
42V POWERNET
Battery
12V
VINH
INH
VW
W
TLE 4271
TLE 4271-2
Traditio
nal
VQ
Q
Quiescent current:
> 800µA @ IQ=0mA
22 µF
VRO
RO
Efficiency:
12% @ 300mA
D
CD
GND
Solutio
n
FB
Quiescent current: V
< 100µA @ IQ=0mA I
less than 100 µA
Efficiency:
76% @ 300mA
Fig. 10: Quiescent current problems in future 42V
systems
New SM
For 42V there is consequently a value of 6mA for each
vehicle and 100µA, or even far less, for each electronic module. The quiescent current requirements are
therefore intensified by at least a factor of 3.
PS Con
VINH
VW
cept
I
BTS
22 nF
22 µF
INH
TLE 6371
(P-DSO-8)
W
LBU =47µH
VQ
Q
DBU
RO
10 µF
VRO
GND
Fig. 12: Proposal for an all-purpose switched voltage
regulator in the 42V PowerNet
Fig. 12 shows a proposal for a switched voltage regulator for the 42V PowerNet with the functionality of the
very popular TLE 4271. Particular development aims
for this voltage regulator are minimized quiescent current, a high level of efficiency in nominal operation,
and low-interference operation with minimal filter
complexity.
The other reason for the problem being exacerbated is
that in future more and more loads will be operated
directly from the battery (terminal 30) with a separate
semiconductor switch. The conventional ignition lock
relay (terminal 15) will become increasingly insignifi5
It is absolutely essential to adapt the bus lines to the
highest occurring overvoltage of 58V. However, as
this measure only affects the bus driver stages it will
have a minimal impact on cost. But since all the components connected to a bus must be able to withstand
this voltage, the bus components in a dual-voltage
PowerNet that are supplied with 12V will also have to
display this property.
As regards the use of switching regulators in the 42V
PowerNet, it can generally be said that, compared to
the linear regulator in the case of 14V, semiconductor
costs are more likely to fall or remain the same, but
that there will be a certain degree of additional expenditure due to employing a coil and additional filter
components.
In many cases this can certainly be compensated by a
more effective structure with less power dissipation
and fewer heat dissipation problems.
5V
12V
SHORT-CIRCUIT PROBLEMS IN THE DUALVOLTAGE POWERNET
Sleep Mode
One of the biggest challenges in a dual-voltage PowerNet is the problem of short-circuiting between 42V
and 14V. To come straight to the point, there is currently no hundred percent solution to this problem in
sight employing simple means.
12V
Operation Mode
5V
Logic
&
Protect
t
CAN Bus
Low speed
CAN
High speed CAN:
5V operation, no sleep
Low speed CAN:
5V operation / 12V sleep
The possible short-circuit points in this type of system
are shown in Fig. 15. It is virtually impossible to prevent short-circuiting directly between the batteries (1,I)
by electrical means; it can only be reasonably precluded through design measures. The same applies to
short-circuit path 2,II, even though the SBT (smart
battery terminal) will provide electrical protection here
in certain circumstances.
LIN, K-Bus:
12V operation / 12V sleep
Fig. 13: Present-day communication chips employ the
12V supply voltage as a working or quiescent current
supply
possible short circuit points between 14 V and 42 V
via interconnection of 1 , 2 or 3 with I , II or III
Adaptation to a 42V PowerNet is unavoidable in the
case of the conventional CAN and LIN communication
interfaces. Fig. 13 shows the operating voltages necessary today for nominal operation and for what is
called ‘sleep mode’. The LIN bus is generally operated
with 12V, while the low-speed CAN is only operated in
sleep mode. This 12V supply would have to be provided additionally in a pure 42V PowerNet, which is
likely to give rise to a massive quiescent current
problem specifically in sleep mode.
1
2
3
14 V
12 V
IBK
12 V
14 V
M
5V
µC etc.
42 V
III
42 V
36 V
IBK
SAM
G
I
M
M
II
Source: DaimlerChrysler
Challenges for Bus Communication at 42V
Short to 42V:
58V max. at bus
costs
CAN, 5V operation:
step down converter
costs
additional 12V power supply
quiescent current
or 42V supply
new specification
LS CAN, sleep mode:
LIN, 12V operation:
additional 12V power supply
costs
or 5V operation
compatibility?
Fig. 15: Short-circuit points in the dual-voltage PowerNet
Short-circuiting will occur most frequently in loads at
level 3,III, which should be electrically protected as
much as possible. The problem is shown in detail in
Fig. 16. To consider it in broad terms, two cases will
be distinguished here: case A with a high-resistance
short-circuit of, for instance, 5A between 42V and
14V, and case B with a short-circuit current of, for example, 100A.
Fig. 14: Necessary modifications to present-day communication concepts for 42V
If the intention is not to provide this 12V supply separately, Fig. 14 shows possible alternatives with a direct
42V supply for the low-speed CAN in sleep mode or
5V nominal operation for the LIN bus. But this would
necessarily result in a changed specification.
6
42 V
10A
42V ECU
D
Problem:
- MOS power stages have a reverse body diode
- Destruction possible under reverse polarity conditions
(Single Switch: limitation of current by load resistance,
Power Bridge or PWM freewheeling: no current limiting!
Aim:
- Definition of central reverse polarity protection with
voltage and time limit
M
S
G
42 V
14 V
VDS < 0
14V ECU
S
Vbat > 16V
D
Switch OFF
communication
A: short = 5A
B: short =100A
M
G
D
5V
12 V
S
G
µC etc.
Fig. 16: Problems and possible solutions in the case
of 42V to 12V short-circuiting
Fig. 17: Semiconductor bridges and systems with a
freewheeling diode must in particular be protected
against polarity reversal of the operating voltage
The 42V switch designed for the 10A nominal current
will not detect any problem in case A with a 5A shortcircuit current. The short-circuit in case A must therefore be detected in the 14V control unit and successfully withstood without any damage occurring until the
problem is eliminated. The short-circuit current in the
14V control unit will initially flow via the reverse body
diode of the load transistor and the 14V cutout to the
14V battery. The 14V cutout may be tripped. The
problem can be detected either through polarity reversal of the 14V load transistor (VDS <0) or raising of the
14V operating voltage followed by limitation by a
zener diode to, for instance, Vbat >16V. The 42V
switch which is the cause could then be identified
through what is called a switch-off search routine and
the short-circuit current disconnected. The 14V control
unit should remain undamaged during this disconnection time in the second range; the connected load may
be destroyed.
Due to the reverse body diode, problems arise in the
event of polarity reversal especially when MOS power
transistors are used. If the current is limited by a load
in the event of polarity reversal, this situation can generally be withstood for a period of several minutes
without destruction. Destruction will take place very
quickly in applications with an additional freewheeling
diode or in bridge applications.
This time to destruction is given in Fig. 18 for a few
selected semiconductor bridges mounted in different
packages as a function of the reverse polarity voltage.
100
t_kill:
t_kill:
t_kill:
Ipeak:
Ipeak:
Ipeak:
t_kill (s) / Ipeak (A)
10
The situation is somewhat clearer in case B. The
overcurrent of 100A must be detected by the 42V
control unit and disconnected within µs. Measurements have shown that even 14V control units with
relatively small and sensitive power switches in SO
packages are not damaged.
P-SO20
tkTLE5205
i ll5 2 0 5
(½/2Vr)V TO220
tkBTS640
i ll6 4 0 (1
s)
SO20
tkBTS771
i ll7 7 1
P-SO20
IpTLE5205
eak5205
) TO220
IpBTS640
e a k 6 4 (½
0 (V
1r/2
V s)
BTS771
SO20
Ip e a k 7 7 1
1
0 .1
Safe
Reverse
Operation
Area
1 .5
2 .0
2 .5
3 .0
3 .5
4 .0
4 .5
n e g a tive s up p ly vo lta g e (V )
Treating the problem of short-circuiting is especially
difficult in cases that are borderline between A and B.
Total protection is extremely costly here or even impossible. A solution to the problem may be approached by statistical means.
Fig. 18: Measured values of destruction due to polarity
reversal on representative semiconductor bridges and
a proposal for what is called a “Safe Reverse Operation Area”
Even very small semiconductor bridges in a SO package are only destroyed after approx. 5s in the event of
–2V reverse polarity voltage; larger bridges can withstand this condition for several tens of seconds. The
higher the reverse polarity voltage, the faster the destruction. With –3V, for example, smaller bridges will
be destroyed in about 200ms. Apart from the time to
destruction, Fig. 18 also shows the relatively high currents flowing.
POLARITY REVERSAL IN THE 42V POWERNET
Polarity reversal in the 14V system is now customary
and often allowed for in the specifications at a value of
–12V for one minute at a start temperature of 25°C.
This specification currently gives rise to considerable
additional costs in each individual control unit. However, due to a lack of possible solutions, many highcurrent applications today do not make adequate provision for reverse polarity protection.
The aim was then to find a safe reverse polarity range
for the reverse polarity specification for 42V which on
the one hand permitted a smaller number of polarity
7
reversals without causing permanent damage to the
power control units, and which on the other hand
would allow simple implementation of central reverse
polarity protection. A reverse polarity range of –2V for
a maximum period of 100ms at a starting temperature
of 25°C was selected as the proposal for standardization. Damage can be precluded in this range for most
semiconductor power end stages, and other components such as electrolytic capacitors should also be
able to withstand this loading. Logic chips and micro
controllers cannot withstand a –2V load without protective measures and must continue being protected
with a series-connected diode. This solution does not
cause any basic problems on account of these chips’
small currents.
Fuel
ISG
Engine
Mechanical
ancillaries
Power
to driven
wheels
Transmission
Power &Control
Electronics
Battery
CAN
42V
42V to vehicle
electrical distribution
system
Source: Ford Motor Co.
Matched Triple
Fig. 19 shows a possible technical implementation of
central reverse polarity protection. A very powerful
high-current diode is mounted near the battery which,
in the event of polarity reversal, clamps the voltage to
–2V and is thermally designed to withstand this condition for 100ms. The flow of current must be disconnected within this 100ms period by means of an additional switch element such as a fuse, relay or semiconductor switch.
Electrical
Loads
42V Battery
Power Limited,
VoltageLimit
Power
Electronics
Source impedance
Power Conditioning
Current Limit
Torque Limit
Ancilliary
Loads
Engine
Friction, inertia, compression torque
Road
Loads
ISG
Transmission
Elec. losses, inertia
Friction, inertia
Failure case: Mix up of terminals at jump start
Realization idea for central protection: Power diode near battery terminals together with
power disconnect switch: relay, fuse or MOSFET
Fig. 20: Power flux in what are called mild or soft hybrid vehicles
– RJSC = Resistance of Jump Start Cable
– RW = Resistance of wiring to Electronic Control Module under test
R JSC
Reverse
42V/14V
Relay or
Fuse or
MOSFET
RW
_
+
-2V, 100ms
+
A particular problems arises for the 42V PowerNet in
connection with what are called mild or soft hybrid vehicles. As can be seen in Fig. 20, vehicles of this type
have an integrated starter generator ISG which,
alongside the starting function, also allows a bidirectional flow of power between transmission and
battery.
worst case
ECM
_
System
voltage
Fig. 19: Proposal for central reverse polarity protection
near the battery for 12V or 42V PowerNets
58 V
50 V
48 V
Ideally the reverse polarity measures in the power
paths can then be omitted in the individual control
units, making reverse polarity protection in the vehicle
economically viable. And this approach also offers an
interesting alternative for the 14V PowerNet.
42V
42V PowerNet Voltage Range
Over voltage
Dyn. operation
Nominal
voltage swing
Static
operation
Voltage
swing
range
during
ISG
torque
control
ISG Bus
Voltage
30 V
Start
swing
Start swing
Dyn. operatin
21 V
Under voltage
No operation
VOLTAGE VARIATIONS IN THE CASE OF MILD OR
SOFT HYBRID VEHICLES
Time
Mode:
Key ON Crank
Source: Ford Motor Co.
Normal Mode/
Generate
Recuperate
Stop/
Restart
Boost
Normal Mode/
Generate
Fig. 21: Voltage variations in mild or soft hybrid vehicles due to high power removal or feed-back of the
integrated starter generator
As already reported at the start, efforts in defining the
42V PowerNet were directed at avoiding excessive
under- and overvoltages so that the individual components could be designed for and operated as closely
as possible to the nominal voltage. Allowing for the
generator and battery technology employed, a voltage
variation of 30V to 48Vrms is permitted in nominal operation; the generator ripple can have a peak value of
50V. With the defined starting profile, the voltage dip
on startup is 21V or 18V.
In the case of normal, engine-driven electric power
generation the voltage of a lead-acid battery is kept
approximately to 42V; the charging voltage should
only rise significantly above 42V when the temperature is low. But if braking energy is to be fed back into
the battery, the battery voltage must be raised to the
maximum value of 48Vrms (50Vpeak) in order to have
8
also help minimize the voltage fluctuations, but this
approach is usually ruled out by cost considerations.
a high power flux. The same applies to the delivery of
electric power to the transmission for improving the
torque. The requirement here is to load the battery to
the minimum value of 30V, as shown in the various
operating states in Fig. 21.
Where DC motors and other single-phase loads are
concerned, Fig. 23 shows a proposed means of implementing the above-mentioned speed regulation
using pulse width modulation PWM. For example, the
switch for a DC fan could be designed as a PWM
switch that sets an effective voltage of, say, 36V on
the load. The motor would therefore run at a constant
speed for operating voltages above 36V, and there
would only be a moderate drop in speed for voltages
below 36V. Constant load conditions would consequently be achieved across a wide voltage range. The
load should then optimally be designed for a 36V
nominal voltage. Inductive loads, as well as resistive
loads and lamps, should be suitable for this method.
Precautions are necessary, however, on account of
the electromagnetic interference. This is dealt with
briefly in the next section.
There is the unpleasant effect of the 42V PowerNet
voltage being subjected to relatively high variations.
Fig. 22 schematically shows a possible frequency distribution for the 42V PowerNet voltage, with a high
frequency value in the 30V and 48V range (bottom
right in Fig. 22) on account of the described hybrid
function. The equally higher frequency in the 45V
range is due to the requirement for optimized charging
conditions at low temperatures for a lead-acid battery.
The optimized charging characteristics at low temperatures produce voltage variations of between approx. 38V and 47V (bottom left in Fig. 22) even without the extreme charging and discharging cycles due
to the hybrid function.
System
voltage
12V Today without lamps
12V Today
Collective
Collective
50V
12
13
14
15
ISG Bus
Voltage
Vbb
42V
12
16
42V PowerNet Voltage Swing
13
14
15
30V
16
Volt
Volt
42V with ISG Soft Hybrid
42V without lamps
Collective
Collective
Time
Load
voltage
30
32
34
36
38
40
42
Volt
44
46
48
50
52
Effective PWM Load Voltage
VLoad
50V
30
32
34
36
38
40
42
44
46
48
50
PWM
Vload eff
52
36V Load
36V
Volt
Source: Ford Motor Co.
30V
Fig. 22: Frequency distribution of different charging
and discharging voltage concepts in 12V and 42V vehicles
Time
Fig. 23: Proposed solution for minimizing voltage
variations by pulse width modulating the load
This requirement for optimized charging voltage has
also applied for a long time to the 14V system (top
right in Fig. 22) with charging voltages up to 16V at
low temperatures. It has not yet been possible to consistently implement this requirement chiefly due to the
reduced service life of the lamps. The frequency distribution of today’s 14V system is shown top left in Fig.
22; compared to the other solutions, this displays the
smallest variation in operating voltage.
OPERATING LAMPS AND SMALL MOTORS ON
42V
Loads that can be operated less optimally at 42V are
primarily incandescent lamps and small motors. 42V
would have a negative impact on the useful life and
optics of lamps; with small motors the trouble is
caused by the thinner wires and longer winding times
during manufacture.
As it will probably not be possible to operate lamps
directly in the 42V PowerNet as is the case today and
that starter generators with energy recovery are very
likely to be used, for better or for worse we will have to
proceed on the basis of the large voltage variance
shown. This naturally poses an extreme challenge to
all other connected loads. It is difficult to imagine an
interior fan or windshield wiper, for example, being
able to respond to voltage variations with variations in
speed. A speed regulating mechanism, for example,
must ensure constant operating conditions here. The
speed of multi-phase motors can be very easily varied
thanks to the electronic control. A larger battery would
An attempt should be made here to operate presentday 12V components directly from 42V using PWM.
Although operation via a DC/DC converter would also
be possible, the additional costs make this an unlikely
approach.
Fig. 24 shows how a present-day 12V door lock can
be operated directly from a 42V supply using a semiconductor bridge with PWM capability. So that a slight
reduction in currents and semiconductor costs can be
achieved nonetheless, an optimum compromise could
9
are not just added but are designed as an overall filter.
7)
8)
Publications and describe how this can be done. A
low-cost solution is presented here for PWM filtering
which does not have to be any more expensive than
pure motor filtering. The effectiveness of the filter and
solution concept has been verified both in the laboratory and in a major vehicle manufacturer’s vehicle trial.
PWM applications accordingly present no insurmountable hurdles.
also be envisaged with 24V components being operated directly from 42V using PWM.
42V
ST1
ST2
IN1
IN2
BTS723
Package P-DS014
RDSON = 2*95m Ω
VBB(AZ) ≥ 65V
Logic
&
Protect
PWM
M
ARCING PHENOMENON IN THE 42V POWERNET
12V
The possibility of arcing in the future 42V PowerNet is
a problem area to which little consideration has been
given to date. The reason is that arcing can occur at
voltages above 15V to 20V, depending on the material
used. With mechanical switches, these are normally
quenched by quickly widening the air gap. The speed
of opening and closing the air gap is frequently not
controllable, however, giving rise to major problems
with arcing.
SPD 28N05
Package: DPAk
RDSON: 26m Ω
VDS(BR) ≥ 55V
Fig. 24: Direct 42V operation of a 12V door lock motor
using pulse width modulation
The only negative aspect of this solution appears to
be the additional complexity for filtering out the PWM
interference. This has proved to be solvable and without necessarily giving rise to extra costs.
Power Switch
Fuse
Connector
Broken Wire
42V
Conducted Emission (peak)
dB[µV]
Arcing and fire problems due to:
- replacing fuse
- plugging and unplugging connectors
- broken wires
- shorts to GND or 12V or 42V
120
110
100
90
80
Shorts
to GND
or 12V
or 42V
Load
70
Possible solutions:
- switch off before or during detected action
- short time interruption to stop arc
- PWM mode during action
60
50
40
30
Fig. 26: Proposed solution for reducing the various
arcing problems associated with a 42V operating voltage
42V-motor
24V-motor
12V-motor
CISPR 25 Class 5 (short duration)
CISPR 25 Class 5 (long duration)
20
10
0
0.1
1
10
100
f / MHz
1000
This phenomenon is especially apparent when
changing a fuse or opening/closing a plug contact
while current is flowing. A wire break or a short-circuit
to ground, 12V, or another inactive 42V wire will basically result in the same problem (see Fig. 26).
Fig. 25: Overview of the conducted emission spectra
of DC motors with different operating voltages
As seen in Fig. 25, every brush-type motor, for example, is a potential source of interference. Shown here
are the conducted electromagnetic interference values
for unfiltered 12V, 24V, and 42V window lift motors of
identical design. It can very clearly be seen that the
12V motor has the highest emissions in the lower frequency range on account of its higher currents; higher
range interference at higher frequencies predominates
for the 42V motor on account of higher brush sparking. So it is not possible to state categorically that the
12V or the 42V motor behaves poorly: they simply
behave differently.
Several possible solutions can be suggested here, but
all based on the same principle of a switching element, such as a power switch, being located in the
current path. In the case of changing a fuse or plug,
the opening of a protective cover, for instance, or a
leading plug contact could be detected and the current
flow interrupted by means of a power switch. In the
case of a wire break or short-circuit, the arc would first
have to be detected by means of its interference
emission before deactivation by the power switch.
Various investigations have already been carried out
10)
here .
To suppress the interference produced by both types
of motor, virtually indistinguishable filters are required
for the brush and commutating interference. If the
motor additionally undergoes PWM, this also has to
be allowed for by a PWM filter. The trick is simply to
ensure that these two filters, and hence their costs,
Permanently disconnecting the current is the simplest
way to quench an arc. For critical applications that
cannot be deactivated at random it is also possible to
10
these. His activities after moving over to power semiconductors in 1993 initially centered on the definition
and application of power switches; he then became
head of Technical Marketing for power semiconductors. Dr. Graf now works at Infineon Technologies AG,
where he is in charge of activities surrounding innovations such as EMC for power semiconductors in vehicles.
envisage briefly interrupting the current flow to quench
sparking. A consistent further development of brief
current interruption is PWM, in either permanent or
transient form, i.e. only while there is a risk of arcing.
The duty cycle or minimum off time of the switch is
here determined by the inductances in the load circuit
or motor energy in the case of electric motors.
The ideal mounting location for the semiconductor
switch is near the battery. This can either be the individual load switch, which will then also perform the
standard switching and protective functions, or a
power switch employed as a pre-fuse and power distributor or as a power manager. At the top wiring level
it can also be a smart battery terminal SBT that will
disconnect virtually the entire PowerNet.
Since 1995 Dr. Graf has been a permanent member
of various international bodies working on introducing
42V in vehicles; he also works on the 42V standardizing committee at FAKRA/VDE and ISO. He was an
st
nd
organizer of the ‘1 and 2 International Congress on
the 42V PowerNet’ in 1999 and 2001.
SUMMARY
REFERENCES
Implementing a 42V PowerNet in vehicles poses a
real challenge to development engineers. On the one
hand it offers countless opportunities and benefits, on
the other there are still many problems of detail that
need solving.
Just as electrifying vehicles will help optimize individual functions, so the aid of electronics can and must
also be rigorously enlisted to resolve the various
problems of detail. Not in all cases do these involve
new, additional semiconductor components; attempts
should rather be made to employ the available functions of existing components such as PWM in order to
find economical solutions to potential problem areas.
This also means adopting novel approaches and setting up development teams with a new directional
thrust. The new problems described cannot be resolved by clinging to conventional solutions such as
manually or electromechanically actuated switches or
conventional fuses. The future of automobile engineering lies in electronics, so we should also embrace
its rigorous application.
1)
Toyota’s `Mild Hybrid´ System Boosts Fuel Efficiency 15%,
Toyota press release, Tokyo, June 12, 2001,
2)
Intelligente Leistungshalbleiter für zukünftige Kfz-Bordnetze,
A. Graf et. al., 17th ‘Electronik im Kraftfahrzeug‘ conference,
Munich, June 3-4, 1997,
http://www.infineon.com/cgi/ecrm.dll/ecrm/scripts/sol_cat.jsp?oi
d=-8259
3)
Automotive Electrical Systems – The Power Electronics Market
of the Future, John G. Kassakian, APEC 2000,
http://auto.with.edu/consortium/
4)
Jump Starting and Charging Batteries with the New 42V PowerNet, Paul Nicastri et. al., 1st International Congress on 42V
PowerNet, September 28-29, 1999, Villach,
http://auto.with.edu/consortium/
5)
Can your Wiring System Lose Weight with a 42V Electrical
System?, Norman Traub, 1st International Congress on the
42V PowerNet, September 28-29, 1999, Villach,
http://auto.with.edu/consortium/
6)
Semiconductor Technologies and Switches for New Automotive Electrical Systems, A. Graf, EAEC European Automotive
Congress, Barcelona; June 30 – July 2, 1999
http://www.infineon.com/cgi/ecrm.dll/ecrm/scripts/sol_cat.jsp?o
id=-8259
7)
42V PowerNet in Door Application, A. Graf, A. Pechlaner SAE
2000 World Congress, Detroit, March 6-9, 2000,
http://www.infineon.com/cgi/ecrm.dll/ecrm/scripts/sol_cat.jsp?o
id=-8259
8)
Driving Small Motors at 42V PowerNet, F. Klotz, A. Graf, SAE
2001 World Congress, Detroit, March 5-8, 2001,
http://www.infineon.com/cgi/ecrm.dll/ecrm/scripts/sol_cat.jsp?o
id=-8259
9)
42V ISG and the PowerNet Standard: Can the two coexist?,
John M. Miller, Franco Leonardi, Kenneth Hampton, Robert
Eriksson, MIT/Industry Consortium, Lisbon, March 26-27,
2001,
http://auto.with.edu/consortium/
GENERAL NOTE
The details given specify technical characteristics;
they do not provide assurance of specific characteristics being present
CONTACT ADDRESS
Dr. Alfons Graf, Infineon Technologies AG, Automotive Power Innovation, Munich.
alfons.graf@infineon.com.
Dr. Alfons Graf studied general electrical engineering
and electro-physics at Munich Technical University.
He gained his doctorate there between 1985-1990 in
the fields of MOS breakdown and laser scanning. In
1990 he began working for Siemens AG on the design
and layout of CMOS ASICs and methods of testing
10) The New Automotive 42V PowerNet: Preparing for Mass Production, conference publication for the 2nd International Congress on the 42V PowerNet, A. Graf et al., Ludwigsburg, April
24-25, 2001,
Expert Verlag, ISBN 3-8169-1992-8
11