mc33981bpna/r2 Freescale Semiconductor, Inc, mc33981bpna/r2 Datasheet - Page 25

• Manufacturer Part Number: mc33981bpna/r2
• Description: Single High-side Switch 4.0 M , Pwm Clock Up To 60khz
• Manufacturer: Freescale Semiconductor, Inc

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
V
Analog Integrated Circuit Device Data
Freescale Semiconductor
I(t) on V
BAT
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 Ω 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 29, Enhanced Board, on page
RC In Filter
Figure 28. 33981 with Filter
Figure 27. VPWR Current
PWR
Duty Cycle
Increase
: 2 x 3 mF and 3.5 uH
SR
3.3 nF
PWR
33981
C3 = 10 nF
33891
and GND: a 2.0 Ω resistor in
GND
OUT
PWR
RC Out Filter
and GND
PWR
25.
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
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
RC Out
EMC AND EMI RECOMMENDATIONS
Filter C2
shows the spectrum of the
TYPICAL APPLICATIONS
RC In
Filter
Filter
PI
33981
25