AN5

Application Note 5
Issue 2 February 1996
Super E-Line Applications in Automotive
Electronics
Replacement of Large Packaged Transistors with an Enhanced TO92
Product
David Bradbury
Car buyers are now demanding greater
and greater sophistication in their
purchases, which along with extra safety
features, pollution controls, security
systems and manufacturing cost-cutting
measures, are leading to an everincreasing use of electronics in
automobiles. Automobile electronics
have extended from the occasional
radio, to cover every major area within a
vehicle. Engine management, fuel
injection system controls, transmission
controls, anti-lock braking systems,
electronic displays, warning systems,
etc., are just a few examples of the wide
range of electronic systems that can be
presently found in modern cars.
Many of these systems involve high
current loads such as relays, solenoids,
lamps, displays, motors and audible
warning systems. These require one or
more power transistors to interface
between the controlling logic and the
load. This brief note explains some of
the major problem areas in selecting
devices and circuits for automobile use,
and demonstrates the use of the Zetex
Super E-Line range of transistors in
some practical examples.
Problem Areas
The hazards for power devices in
automotive electronic systems are both
mechanical and electrical. The
mechanical hazards centre on the
extreme operating temperature range
endured by the devices.
To help designers evaluate the
performance of Super E-Line transistors
as temperatures vary, Zetex can supply
a wide range of temperature-related
data on both standard and special
characteristics. Figure 1 shows the
standard data sheet VCE(sat) against IC
grap h for a Z TX602 S uper E-Line
Darlington transistor. Note how the
characteristics are shown for a range of
temperatures. Even when this data is not
given on the data sheet, Zetex can
supply this quickly for customers who
require such information.
Mechanical Requirements
Passenger compartment temperatures
can vary from - 40°C to + 85°C with the
engine compartment ambient reaching
as high as 120°C. High ambient
temperatures place serious constraints
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Application Note 5
Issue 2 February 1996
Zetex Super E-Line and E-Line bipolar
transistors are encapsulated in a special
Silicone plastic that allows operation at
junction temperatures up to 200°C. This
gives
them
the
temperature
performance of Metal Can devices with
the robustness and low cost of a plastic
encapsulation. Figure 2 illustrates some
of the advantages given by the E-Line
package. It compares the power rating
against ambient temperature of the
Super E-Line 1W package, with standard
TO92, TO237 and TO220 style packages.
1.8
-55°C
+25°C
+100°C
+175°C
1.6
1.4
1.2
IC/IB=100
)taV
s(E)CstloV(
1.0
0.8
0.6
0.4
0.2
0
0.01
0.1
1
10
IC - Collector Current (Amps)
VCE(sat) v IC
Figure 1
Typical Collector Emitter Saturation
Voltages vs Collector Current, with
Temperature as a Parameter.
1.0
Power Dissipation (W)
on the performance and reliability of any
power semiconductors used. As a result,
Metal Can encapsulated devices or
plastic types that are grossly overrated
are normally required. However, Zetex
manufacture a range of inexpensive
medium power transistors that are
ideally suited to these severe operating
conditions.
1.6W 25 °C
0.8
TO220
TO237
0.6
TO92
0.4
ZETEX
E-Line
0.2
0
0
40
80
120
160
200
Ambient Temperature ( °C)
Figure 2
Power Derating Curves Showing Power
Dissipation Advantage of the E-Line
encapsulation.
Note how standard TO92 and TO237
types give inferior performance to that
of the E-Line range, with even the TO220
style devices requiring a heatsink to
match E-Line types in ambient
temperatures above 110°C. Also, even
higher levels of power dissipation are
permissible if the E-Line devices are
mounted on circuit boards with a low
thermal resistance. For instance, devices
fr o m th e S upe r E -L in e range can
dissipate 1.5W when mounted on a
circuit board providing 1 square inch
copper area to the collector termination.
Furthermore, pulse applications allow
higher powers still. Figure 3 shows the
actual power dissipation permissible for
a ZTX650 mounted on a 1 inch square
board for a range of pulse widths. This
chart can be used for design analysis
when using any of the ZTX649-658 and
ZTX749-758 transistor ranges.
Extensive reliability testing has been
done on the packaging and chips that
m a k e u p t h e Z ete x E-L ine r ang e,
confirming both power ratings and
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Application Note 5
Issue 2 February 1996
quality. Temperature cycling, climatic
and electrical life evaluation tests are
routinely carried out on all of the Zetex
discrete products to guarantee
continuing quality.
120
Thermal Resistance ( °C/W)
DC THERMAL RESISTANCE (116.7 C/W)
100
80
happen and efforts should be made to
limit their seriousness.
Application Examples
The design of load driver circuits which
operate uslng a vehicle’s normal battery
voltage range, comes from a fairly
straightforward consideration of drive
le v e ls , outpu t c ur r e nt and pow er
dissipation.
60
240
40
200
Single Pulse
20
160
-t/350µs
V=240e
Supply
0
1ms
10ms
100ms
1s
10s
100s
Voltage
(V)
Pulse Width
Figure 3
Transient Thermal Resistance for a
ZTX650 Series Transistor Mounted on
a 1" square FR4 PCB.
120
80
40
14.2V
0
0.25
0.5
0.75
1.0
1.25
1.5
1.75
2.0
Time (ms)
Electrical Requirements
Before moving on to some
a p pli c at i o n e xam ple s , it is wor th
highlighting some of the electrical
hazards that affect their design. Apart
from normal 10-15V operation,
automotive electronic systems have to
withstand a wide range of transients.
These include reverse battery
connection, double voltage supplies, a
240V/0.5J positive line transient, an
80V/50J load dump transient, a
-100V/0.5J supply disconnect transient
and many other lower energy but higher
voltage transients. Figures 4 and 5 show
the voltage waveforms of the first two of
these transients. A further requirement
is that the system can withstand a
reasonable amount of mistreatment
during maintenance. Accidents do
Figure 4
Common Automotive Transients 240V Line Transient.
Reverse battery protection and transient
protection, however, can be achieved in
number of ways, with occasionally some
conflict of effect. In the following
application examples, consideration is
given to the problems of designing load
driver circuits for automobile use.
Figure 6 shows a simple unprotected
lamp driver circuit. In this circuit, a
reverse connected battery would force
current through the collector-base
junction of the output transistors and
in to the co ntrol IC, with possibly
disastrous consequences. One good
solution to this problem is to insert a
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Application Note 5
Issue 2 February 1996
depend on the type of transient
protection employed.
Supply Voltage (V)
80
60
-t/230ms
V = 80 e
40
20
14.2V
0
100
200
300
400
500
Time (ms)
Figure 5
Common Automotive transients - “Load
Dump”.
diode in series with the supply (shown
dotted). This provides excellent
protection, but at the expense of a 0.7V
voltage drop, which in some
applications may be unacceptable. A
second solution is to add a diode across
the collector-emitter terminals of the
output device. This diode shorts the fault
current to ground, thus protecting the
transistor and drive IC without causing
any voltage drop in normal operation.
However, which reverse battery
protection technique used may well
The wide range of transients that occur
within an automobile often require a
number of different protection
techniques to be employed. Two
strategies are common when dealing
with the 80V load dump transient that
can be caused if the battery becomes
disconnected whilst the alternator is
charging. These are to clamp the
transient with a low-voltage zener or
VDR, or to use an output transistor
whose breakdown voltage is greater
than the transient. Figure 7 illustrates the
clamp method. Using a voltage clamp
allows a high performance, low voltage
transistor such as the Zetex ZTX449 to
be used as the output device. The clamp
component has to withstand a current
that is several times greater than the
normal current taken by the load. This
can cause very high power dissipation in
the clamp for heavy loads, so the
technique is normally restricted to lower
current load drivers.
Using a high voltage transistor (i.e.
gre ater than 80V) makes a clamp
+12V
+12V
Protection
Diode
Lamp
Relay
C27V
Control
Logic
Control
Logic
ZTX
653
ZTX
449
0V
0V
Protection
Diode
Figure 6
Reverse Battery Protection.
Figure 7
Transient Clamp using a Low Voltage
Driver and High Current Zener Diode.
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Application Note 5
Issue 2 February 1996
unnecessary for the load dump
transient. The current handling
capability of high voltage transistors of
a given chip size are generally not as
good as their low voltage counterparts,
but Zetex can offer suitable Super
E-Line transistors with a 2A continuous
rating (The 100V ZTX653 for instance).
Using a high voltage transistor does not
completely eliminate the need for some
form of clamp circuit. Transients as high
as 500V can occur in an automobile, and
measures must be taken to limit these.
However, these high voltage transients
are low energy types which can be easily
controlled using a low power clamp
+12V
Solenoid
Control
Logic
ZTX
653
C82V
0V
Figure 8
High Voltage Driver with Low Current
Rated Transient Clamp.
all too easily happen (cleaning
connectors with a screwdriver, for
instance) and so it can be very
worthwhile to protect the driver circuit
against this possibility. Figure 9 shows
an output circuit which includes a
short-term current limit function to
protect the output transistor.
The characteristics of the circuit block
labelled CONTROL LOGIC in the
previous diagrams can be important
when selecting output devices. Often
this element is constructed using low
output current MOS or CMOS circuits.
Since many loads such as lamps and
relays can under some circumstances
take surge currents in excess of 1 A, the
output devices used must either employ
interface circuits or have very high
current gain. This high gain can be
achieved by using MOSFET or
Darlington transistors. For instance, the
Zetex ZVN4206 MOSFET transistor
could be substituted for the ZTX449 in
Figure 7, allowing a low output current
logic circuit to be used. Zetex also supply
NPN and PNP Darlingtons that are
+12V
circuit. Thus, the circuit when using a
high voltage output transistor (shown in
Figure 8) looks identical to the low
voltage clamp circuit of Figure 7,
however the power rating of the clamp
component (and it’s cost) will be much
lower.
Any load that can be removed from the
circuit, such as a lamp bulb that can be
unscrewed or a relay that can be
unplugged, may be a potential
reliability
hazard
during
maintenance. Accidental shorts can
C82V
ZTX
653
Control
Logic
Solenoid
0V
Figure 9
Load driver with current limit.
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Application Note 5
Issue 2 February 1996
equally suitable for these applications.
Figure 10 shows a four-phase stepping
motor driver using ZTX600 Darlington
transistors, directly driven from a CMOS
microprocessor.
+12V
Four
Phase
Motor
+5V
ZTX
600
ZETEX Super E-Line Product
Range
4
3
Tables 1 and 2 within Appendix A show
some of the wide range of Zetex Super
E-Line devices that can be useful in
automotive applications. The tables can
be used to choose the best device to suit
the particular circuit requirements of
voltage, current and gain. The gain and
current specifications of a load driver are
normally easy to calculate, but as
mentioned previously, the breakdown
voltage required is dependent on the
transient protection method used.
µP
2
1
C8
ZTX
600
ZTX
600
ZTX
600
0V
Figure 10
Four Phase Stepper Motor Drive Circuit
using ZTX600 Darlington Transistors.
Most medium power E-Line and Super
E-Line devices can now also be supplied
in the centre collector lead
configuration. This allows the superior
performance of the Zetex Super E-Line
and E-Line range to be utilised in
replacing TO202, TO220, TO237, SOT89,
TO126, TO225 and many other packages
without the expense of re-tooling circuit
boards.
Additionally, many of the devices listed
are available in the surface mount
SOT223 package.
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Application Note 5
Issue 2 February 1996
Appendix A
A selection of some of the Zetex range of products particularly suited to Automotive
applications. For full characterisation refer to Data Book.
NPN
PNP
ZTX649
ZTX749
ZTX650
ZTX750
ZTX651
ZTX751
ZTX652
ZTX752
ZTX653
ZTX753
UNITS
VCBO
35
60
80
100
120
V
VCEO
25
45
60
80
100
V
VEBO
5
V
ICM
6
A
IC
2
A
PTOT
1
W
hFE
min
75 @
IC=2A, VCE=2V
80 @
IC=1A, VCE=2V
55 @
IC=1A,VCE=2V
hFE
min
15 @
IC=6A, VCE=2V
40 @
IC=2A, VCE=2V
25 @
IC=2A, VCE=2V
VCE(sat)
max
0.5V @ IC=2A, IB=0.2A
V
Table 1
ZTX649-653 & ZTX749-753 Series Main Parameters.
ZTX602
ZTX603
ZTX604
ZTX704
ZTX605
ZTX705
UNITS
VCBO
80
100
120
140
V
VCEO
60
80
100
120
V
NPN
PNP
VEBO
10
V
ICM
4
A
IC
1
A
PTOT
1
W
hFE
min
500 @
IC=2A, VCE=5V
hFE
min
2000 @
IC=1A, VCE=5V
VCE(sat)
max
1.0V @
IC=1A, IB=1mA
2000 @
IC=1A, VCE=5V
1.5V @
IC=1A, IB=1mA
Table 2
ZTX602-605 & ZTX704-705 Series Main Parameters.
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