N6752A - Agilent / Hewlett-Packard

Description

The automobile electrical

system is poorly regulated and

subject to frequent dips and

overshoots. Voltage can range

from 11 to 15 volts under

normal conditions and from

8 to 24 volts under transient

starting and running conditions.

As a result, voltage margin

testing is a necessary part of

testing Engine Control Units

(ECUs) to verify proper opera-

tion and tolerance for extreme

bias voltage conditions.

Problem

Every second of test time counts

in the competitive automotive

electronics marketplace. Testing

at multiple bias voltage levels is

a necessary, but time consuming

part of ECU testing. Most system

DC sources available require

significant time to change and

settle to a new output setting,

adding several seconds to the

overall test time.

Solution

Agilent Technologies N6700

Modular Power System and

N6752A power supply module

incorporate features that

reduce ECU test time and

enhance testing, including:

•The N6752A 50 V, 10 A,

100 W autoranging power

supply module features active

down programming for fast

output downward transitions

regardless of load.

•Less than 1 millisecond

command processing time

reduces test time.

•Less than 4 milliseconds

output response time reduces

test time.

•Identical modules can be

paralleled and operated as

a virtual single output for

greater output current and

power, for testing higher

power ECUs.

•Up to four modules fit in the

1-U high mainframe, saving

test system space.

ECU Input and Output Characteristics

An ECU takes a myriad of

signals monitoring the vehicle

and its environment. In turn

it manages and controls the

engine and ancillary equipment

for optimum operation. Figure 1

summarizes the many input and

output signals of a typical ECU.

Increase Automotive ECU Test Throughput

Application Note 1505

DC Power Input Communication Interface

VBattery CAN bus

Static Analog Inputs Static Digital Drive Ouputs

VBattery sense Fuel pump

Engine temperature Check engine light

Air temperature A/C cutout relay

Manifold Absolute Pressure (MAP) Fan relay

Mass air flow rate EGR solenoid

Exhaust oxygen (Lambda) Purge canister solenoid

Throttle position Diagnostics code readout

Dynamic Analog Inputs Dynamic Digital Driver Outputs

Engine knock Fuel injectors

Ignition coils

Static Digital (or Switched) Inputs Static Analog Outputs

Ignition switch: off, acc., on, crank Regulated voltages or currents for sensors

Acc. on/off; A/C, heater, brake, lights

Throttle idle position

Diagnostic mode

Dynamic Digital (or Pulsed) Inputs Dynamic Analog Outputs

Vehicle speed Idle speed control servo

Camshaft/engine speed

Camshaft/engine position

Figure 1. ECU Inputs and Outputs

In ECU functional test, appro-

priate test system resources

emulate the various input

signals in a controlled manner

and load and check the out-

puts for correct response. It is

readily apparent based on the

number of inputs and outputs

that test system resources for

ECU test is quite extensive.

Key Bias Voltage Levels in

Automotive Electrical Systems

Depending on the operating

state of the vehicle, certain

voltage levels are commonly

encountered in an automotive

electrical system. These levels

become key voltages for ECU

test, as illustrated in Figure 2.

Some relevant tests at key

voltages include:

•Continuity between multiple

ground, power and high

current driver pins is

checked with the power

supply set to zero or

disabled.

•Shorts or other unexpected

faults can be checked by

applying a very low voltage

and measuring the resultant

current.

•Various functional tests

are run from a low level of

around 8 volts, representing

starting, up to high level of

around 15 volts, representing

full charging conditions.

•The ECU voltage monitor

circuit, if included, is

calibrated or verified, typically

by applying two end-point

operating voltages at

minimum.

•The ECU low voltage reset

level is verified by checking

its minimum “must not trip”

and maximum “must trip”

thresholds.

In all, an ECU may be subjected

to up to 20 bias voltage level

changes during test.

Voltage

Test Activity

18 V

12 V

6 V

Check pin

continuity

0 V/disabled

Check DUT

for faults

Nominal

voltage

12.6 V

Charge

voltage

13 – 15 V Discharge

voltage

11 – 12 V

Start

voltage

8 – 10 V

Calibrate & verify

voltage monitor

6 – 10 V

Check reset

voltage

Does

not trip

< 6 V

Trips

Perform functional tests

1 V

Figure 2. Key Bias Voltage Levels

Power Supply Output

Response Time

A few steps occur when changing

a power supply output voltage

setting to a new value, as

depicted in Figure 3. These steps

all take a finite amount of time.

Once a command is received

by the power supply-it must

process it; this is its command

processing time. The power

supply’s output then responds

and changes to the new setting.

The time it takes to reach its

final value, within a certain

settling band, is its output

response time. A 1% settling

band is suitable for ECU test.

Table 1 compares the command

processing and output response

times of many typical program-

mable power supplies to the

N6700 and N6752A. The

excep-

tional speed characteristics

are

a result of being designed for

high throughput test

applications.

It is especially important to

take note of down program-

ming output response time.

Many power supplies depend

upon the actual loading of the

DUT to bring the voltage down.

Under light loading conditions

it can take a second or more

for some power supplies

without down programmers

to reach their final value. The

N6752A power supply module

incorporates an internal down

programmer for fast down

programming, independent

of the load. Both fast up and

down programming speed is

important in ECU testing.

Throughput Improvement Using

Agilent Technologies N6700

Modular Power System and

N6752A Power Supply Module

The test time reduction achieved

by switching to the N6700

and N6752A from a slower

power supply is a product

of the command processing

and output response time

improvement and the number

of output voltage transitions.

A 200-millisecond time improve-

ment and 15 output transitions

yields a 3 second test time

reduction. For an ECU having

a 20 second test time, this

translates to a 15% improve-

ment in throughput. Such an

improvement is highly valued

by ECU manufacturers, greatly

reducing their cost of test and

providing immediate benefit.

Related Applications

•

Automotive Electronic

Control Modules (ECMs)

•

Automotive Body Electronics

•

Automotive Telematics

Voltage

Time

Final

value

Initial

value

< 1% typical

settling band

Command

sent

Command

processed

Output

responded

Figure 3. Power Supply Command Processing and Output Response

Parameter Agilent

N6700A/N6752A

Typical System DC Sources

Command Processing Time < 1 millisecond 20 to 50 milliseconds

Output Response Time ≤4 milliseconds to 50 mV 50 to 500 milliseconds to <1%

Table 1: Command Processing and Output Response Times

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Product specifications and descriptions

in this document subject to change

without notice.

Printed in USA, October 22, 2004

5989-1682EN

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