TYPICAL APPLICATIONS
EMC AND EMI RECOMMENDATIONS
Figure 21 illustrates the typical application diagram.
measurement method to measure both conducted and
radiated emission.
CONDUCTED EMISSION MEASUREMENT
Conducted emission is the emission produced by the
device on the battery cable. The test bench is described by
CISPR25 (see Figure 23, Test Bench for Conducted
Emission, on page 23).
The Line Impedance Stabilization Network (LISN), also
called Artificial Network (AN), in a given frequency range
(150 kHz to 108 MHz) provides a specified load impedance
for the measurement of disturbance voltages and isolates the
equipment under test (EUT) from the supply in that frequency
range.
Figure 21. Typical Application Diagram
APPLICATION
2000+ 200mm
Contact to
Ground Plane
Engine cooling, air conditioning, and fuel pump are the
targeted automotive applications for the 33981. Conventional
solutions are designed with discrete components that are not
optimized in terms of component board size, protection, and
diagnostics. The 33981 is the right candidate to develop
lighter and more compact units.
LISN
+
Ground
Power Supply
BF Generator
-
Out
EUT
Load
Non-Conductive
Material
High Side Driver Signal
Electrical to Optical
Converter
Coaxial Cable
DC motor speed adjustment allows optimization of energy
consumption by reducing supply voltage, hence the mean
voltage, applied to the motor. The commonly used control
technique is pulse wide modulation (PWM) where the
average voltage is proportional to the duty cycle. Most
applications require a PWM frequency of at least 20 kHz to
avoid audible noise. Figure 22 illustrates typical waveforms
when switching the 33981 at 20 kHz with a duty cycle of 80%.
Ground Plane in Copper
12V Power Supply
Spectrum Analyzer
Figure 23. Test Bench for Conducted Emission
The EUT must operate under typical loading and other
conditions just as it must in the vehicle so maximum emission
state occurs. These operating conditions must be clearly
defined in the test plan to ensure that both supplier and
customer are performing identical tests.
The output voltage (OUT) and current in the motor (IMOTOR
waveforms are represented.
)
For the testing described in this application note, the out
pin of the 33981 was connected to an inductive load (0.47 Ω
+ 1.0 mH) switching at 20 kHz with a duty cycle of 80%. The
output current was 17 A continuous.
OUT
Imotor (10A/div)
The ground return of the EUT to the chassis must be as
short as possible. The power supply is 13.5 V.
MC33981 OFF
MC33981 ON
RADIATED EMISSION MEASUREMENT
The radiated emission measurement consists of
measuring the electromagnetic radiation produced by the
equipment under test. CISPR 25 gives the schematic test
bench described in Figure 24, Test Bench for Radiated
Emission, on page 24.
Figure 22. Current and Voltage waveforms
To measure radiated emission over all frequency ranges,
several antenna types must be used:
HOW TO MEASURE ELECTROMAGNETIC
EMISSION ACCORDING TO THE CISPR25
• 0.15 MHz to 30 MHz: 1.0 m vertical monopole in vertical
polarization.
• 30 MHz to 200 MHz: a biconical antenna used in vertical
and horizontal polarization.
One EMC standard in the automotive world (at system
level) is the CISPR25, edited by the International
Electrotechnical Commission. This standard describes the
• 200 MHz to 1,000 MHz: a log-periodic antenna used in
vertical and horizontal polarization.
33981
Analog Integrated Circuit Device Data
Freescale Semiconductor
23
FREESCALE [ Freescale ]
