New Solutions Emerge for Functional Testing of Automotive Electronics

Vehicle electronics present significant problems for automotive testing. High currents and voltages are present in the form of complex signals both as stimulus and as measurements. Much of the circuitry involves asynchronous timing and events. To compound the difficulties, many tests must be performed quickly—in less than 30 s for engine control units. And parametric-level tests—including transistor Vsat, rise and fall times, resistance and capacitance, and diode and zener clamp and knee characteristics— must be executed on the components on the periphery of the DUT.

These two- and three-lead components must be functionally tested as much as the microcontrollers and digital-to-analog converters (DACs) of the DUT, because they interface it to the harsh signals of the vehicle environment. Simple tests of these components may fail to detect faults that can appear at the system level, meaning that the DUT may fail in the vehicle after passing manufacturing test.

As shown in Figure 1, a typical engine control unit (ECU) operates as a closed loop. To test a typical ECU, the test engineer must provide interactive stimulus and response. Testing ECUs also requires a realistic environment that emulates conditions existing in the vehicle.

Passive loads, special custom fixturing and custom interface cards, while traditional in functional testers, are not suitable for high pin-count ECUs. Not only is this type of equipment difficult to calibrate, manage and control in software, but it also slows test throughput and is costly to support and maintain. Whenever a load/interface board is wired into a test fixture, even if comprised of a handful of components, costs for materials, documentation, debug, characterization and maintenance can skyrocket into the thousands of dollars.

Test engineers functionally testing modules for engine control, airbag and anti-lock brake activation, and comfort, audio and navigation systems need more to choose from than merely an increasing number of instruments and software tools. Intense time-to-market pressure demands tools that accelerate test development. Potential for catastrophic failure in electronic safety modules demands tools that produce better and more complete functional test, including creating realistic DUT environments. In an industry that worries about pennies, test engineers need standards-based solutions that deliver sustained economic return.

Control Module Tests

Closed-loop testing is akin to a juggling act. First, inputs influence the outputs of the DUT. As a result, the DUT expects corresponding changes in the sourced inputs. For the engine controller in Figure 1, examples of functional tests include:

Power-up testing, including overall current, stability and ground paths.

Speed/throttle control-loop testing of the emulation of the manifold atmospheric pressure (MAP), throttle position and coolant temperature sensors, usually accomplished using DACs or arbitrary waveform generators (arbs). The ECU responds to these signals, usually precipitating closed-loop iterative adjustments to the DAC or arb phase, frequency and amplitudes.

Exhaust gas recirculation (EGR) Loop Tests in which exhaust sensors are simulated and ECU responses measured in a closed-loop manner. As with the throttle tests, an arb with floating outputs is used to emulate crank and other variable reluctance sensors (VRS), detonation (anti-knock) and rpm/speed sensors.

Individual DUT I/O pin parametric tests to measure bias currents and input impedances and output pin characteristics, including clamp tests, saturation levels, leakage currents and flyback levels when automotive inductive loads are attached.

Tests of fail-safe, enabling, disabling and other ECU control circuits which respond to bus commands; states provided from other ECUs, such as an airbag; or other switches and sensors.

Tests involving interoperation with other modules in the automobile, such as fan relay controls; door and passenger comfort controls, and other relay and actuator circuits.

Not all these tests are created using traditional techniques. Many require closed-loop iterative test procedures.

More challenges involving the high voltages are often encountered, such as measuring flyback voltages from ignition coils (with peaks of greater than 450 V and saturation levels of 1 V). As with this and many other unique test conditions, the challenge is to route the DUT signal to measurement hardware efficiently and cleanly so that multiple measurements can be quickly made.

For the ignition coil test, the best method attenuates the flyback while not attenuating the saturation levels. Similarly, crank or VRS can be simulated with arbs.

In the closed loop, there is a need to change the frequency and amplitude of this signal on the fly and maintain phase continuity with the previous waveform. In addition, VRS signals from wheel-speed sensors often have peak voltages up to 170 V. Instrumentation must handle these voltages and separate the impairment of significant crosstalk.

Automotive Functional ATE

Fortunately, a new category of test solutions for automotive functional test is emerging. Test equipment manufacturers and system integrators are using VXI as an enabling technology to create test systems that feature the tools and capabilities common to ATE systems. With these easier-to-use ATE-like tools, the automotive test engineer can more easily migrate to VXI and get the benefits of standard, modular instrumentation without having to learn how to build a custom VXI system.

However, it’s the software that makes these new automotive functional test systems valuable to automotive test engineers. Test executives, push-button test programming, automated shorts-test development, automatic connecting and routing through switch-matrix switches, and libraries of automotive-specific measurement routines reduce test development cycles by more than 50%.

Applying VXI

The instruments in an automotive functional test system must handle the high voltages and currents, bandwidths and timing that are characteristics of automotive DUTs. VXI is a particularly good technology for closed-loop testing because of its high integration on the P2 connection; for example, with VXI triggers.

As VXI continues to mature, particularly in the area of software standardization such as VXIplug&play, test engineers can expect more platform-level solutions. Increasingly as well, system integrators will add value by developing software that speaks the DUT language; that is, provides routines specific to automotive measurements. Good examples are virtual instrument drivers or push-button functions that test MAP, VRS, EGR, oxygen and other sensors using the nomenclature of the sensor, not bits of an arb.

Tuned Instrumentation

Switching and Matrix Modules: Many automotive DUT signals are analog, and test engineers often want to place any instrument to any DUT I/O pin. They want to handle multiple DUTs and DUT variants where I/O pin functions change. For example, an ECU module with more than 130 pins will quickly overextend the capabilities of general-purpose scanners in which many modules must be stacked and treed to allow all instruments to connect to all pins.

One way to solve this problem is to collocate or embed a multiplexer within centralized measurement instrument functions that handle high voltage, current and trigger sensing. Automated instrument-port-to-DUT-I/O-pin programming is mandatory in either case because test engineers don’t want to be encumbered by stacks and sequences of relay calls or graphics. Automated switching software can follow a simple connect-this-instrument-to-this-DUT-pin language.

General-purpose VXI switch modules typically switch and settle in 50 to 100 ms. To achieve very fast test times, custom switching modules using ATE switching techniques can do the same in 1 to 5 ms. These switch modules contain level translation circuits and conditioning for triggers, both input and output, which map into the VXI trigger bus. These allow connection to the DUT signals while eliminating costly DUT fixture circuits.

Event detection based on time-stamping rather than vectors or fixed clocking: Events on an ECU are both synchronous and asynchronous, and test specs typically allow for a range of acceptable timing. Since these signals are analog and numerous, instrumentation must accept many signals of wide levels and time-stamp them when they change.

Without tuned instruments, it is necessary to use home-brewed setups that tie logic analyzers through level-shifting interfaces to the DUT. Event-based detection and recording instruments serve the application better.

Voltage/current utility instrument: A multifunction VXI instrument with integrated instrument MUX and voltage/current sources is used to test the parametrics of components, such as R, L, C, D, CR, Z and Q. As shown in Figure 2, it can characterize with both high and low voltages, so level shifting is not needed in the DUT fixture.

Arb outputs float: Sensors in automobiles float. Consequently, it makes sense to provide arb outputs that float so that they can be isolated from the test system and DUT.

Flexible loading and other emulation of the DUT environment: A schematic of a typical ECU module reveals many I/O ground and current-source connections. These require loading and clamp tests to provide a realistic test environment. A load card box allows the insertion of passive loads that can be used to verify these return paths, enabling voltage and current measurements and waveform digitizing.

One way to attach these loads to a DUT is to include components and switching in the fixture, but such an approach leads to calibration and correlation-between-multiple-system problems. A better, tuned approach uses an integrated load-box that allows the test engineer to place many kinds and combinations of loads on DUT pins.

With a load box, every pin of the ECU can be switched to one or more loads during test. When this capability is integrated in the subsystem, costs associated with fixtures, debugging and documentation are reduced. Simulating the DUT environment via integrated connections with the instrumentation can significantly reduce the costs of fixturing and documentation and simplify debug and maintenance.

Serial communications: All of the instrumentation and controls must work with serial automotive buses accessed within tests or procedures, asynchronously or synchronously. Manufacturers use variations of RS-232 protocols; ISO-9141, J1850 and variants; Controller Area Network, Vehicle Area Network and other protocols. Drivers and other push-button routines integrate the commands expected or returned for tests written for anti-knock, VRS and other DUT functions.

Summary

The combination of open VXI systems, high-speed test software and automotive-specific instruments provides test engineers with an expandable and flexible architecture that is cost-effective. Time-to-market is reduced because test development time is slashed with software tools that automate programming. These same software tools promote reuse of tests that can be shared among departments.

Costs are reduced because users purchase instrumentation and system configurations that correspond to need. Automotive-specific custom instruments utilize VXI speed capabilities and allow testing of complex engine control modules in well under a minute without compromising fault coverage.

Reduced test development time, use and reuse of proven test routines and an integrated DUT environment which eliminates the costs and hassles of complex DUT fixtures provide substantial economic return-on-investment. These new instruments and measurement capabilities, thanks to open architecture standards like VXIplug&play, are a long-term solution that will evolve with the needs of the users.

About the Authors

Kim Mast joined the Hewlett-Packard staff 12 years ago and today is the Program Manager for the HP TS-5450 Automotive Electronics Test System. He is a graduate of the University of Illinois with B.S.E.E., M.S.E.E. and M.B.A. degrees.

Janet Smith is a Product Marketing Engineer with Hewlett-

Packard’s Measurement Systems Division. She has been affiliated with the company since 1981 in a variety of marketing positions. Ms. Smith graduated from The Colorado College.

Hewlett-Packard Co., Manufacturing Test Division and Measurement Systems Division, P.O. Box 301, Loveland, CO 80539, (970) 679-5000.

June 1995