MC33981BHFK Freescale Semiconductor, MC33981BHFK Datasheet - Page 28

• Manufacturer Part Number: MC33981BHFK
• Description: HF 4.0MOHM RDSON SWITCH
• Manufacturer: Freescale Semiconductor

EFFECTS OF SOME PARAMETERS
When the duty increases the di/dt on the VPWR line is higher.
The device has to deliver more current and provide more
energy.
on the V
level rises with the output frequency. This is due to the
increasing number of commutations.
HOW TO REDUCE ELECTROMAGNETIC EMISSION
turn OFF with SR capacitor, the electromagnetic emissions
can be reduced.
the board filtering and routing that have a big impact on EMC
performances).
external components to the initial board:
represented in
28
33981
V
TYPICAL APPLICATIONS
EMC AND EMI RECOMMENDATIONS
I(t) on V
BAT
The conducted emissions level rise with the duty cycle.
By adjusting the slew rate of the device during turn ON and
Conductive emission tests were performed (taking care of
An optimized solution was found by adding the following
• PI filter on the V
• RC IN filter between V
• RC Out filter between OUT and GND: a 4.7  resistor
• Capacitor C1 of 10 nF between V
• Capacitor C2 of 10 nF between OUT and GND
• Capacitor C3 of 10 nF between OUT and V
• Capacitor SR of 3.3 nF
The EMC enhanced board with adapted value filter is
BAT
series with a 100 nF capacitor
in series with a 100 nF capacitor
PI filter
3.5 μH
3000 μF
Figure 27
PWR
current waveform. The conducted emission
Figure
RC In Filter
Figure 28. 33981 with Filter
Figure 27. VPWR Current
describes the effect of duty cycle increase
PWR
29.
Duty Cycle
Increase
: 2 x 3 F and 3.5H
SR
3.3 nF
PWR
33981
C3 = 10 nF
33891
and GND: a 2.0  resistor in
GND
OUT
PWR
RC Out Filter
and GND
PWR
t
enhanced board and the initial board. The improvement is
appreciatively 15 dB to 20 dB in the all frequency range. The
enhanced board is now in accordance with the Class 3 limits
of the CISPR25 standard for conducted emission.
RADIATED MEASUREMENTS
characteristic of the device relating to radiated emission.
Measurements have been done in accordance with the
CISPR 25 standard as shown in
was the EMC enhanced board.
SR
C3
C1
The chart in
Figure 30. Conducted Emission Spectrum for 33981
This test was performed in order to evaluate the
Figure 30
Figure 29. Enhanced Board
Analog Integrated Circuit Device Data
RC Out
Filter C2
shows the spectrum of the
Figure
Freescale Semiconductor
31. The tested board
RC In
Filter
Filter
PI