33981 datasheet(25/37 Pages) FREESCALE

25 / 37 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33981

TYPICAL APPLICATIONS

EMC AND EMI RECOMMENDATIONS

Figure 27. VPWR Current

HOW TO REDUCE ELECTROMAGNETIC EMISSION

By adjusting the slew rate of the device during turn ON and

turn OFF with SR capacitor, the electromagnetic emissions

can be reduced.

Conductive emission tests were performed (taking care of

the board filtering and routing that have a big impact on EMC

performances).

An optimized solution was found by adding the following

external components to the initial board:

• PI filter on the VPWR: 2 x 3 μF and 3.5μH

• RC IN filter between VPWR and GND: a 2.0 Ω resistor in

series with a 100 nF capacitor

• RC Out filter between OUT and GND: a 4.7

Ω resistor

in series with a 100 nF capacitor

• Capacitor C1 of 10 nF between VPWR and GND

• Capacitor C2 of 10 nF between OUT and GND

• Capacitor C3 of 10 nF between OUT and VPWR

• Capacitor SR of 3.3 nF

Figure 28. 33981 with Filter

The EMC enhanced board with adapted value filter is

represented in Figure 29.

Figure 29. Enhanced Board

The chart in Figure 30 shows the spectrum of the

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.

Figure 30. Conducted Emission Spectrum for 33981

RADIATED MEASUREMENTS

This test was performed in order to evaluate the

characteristic of the device relating to radiated emission.

Measurements have been done in accordance with the

Duty Cycle

Increase

I(t) on V

BAT

33891

3.3 nF

PI f

ilter

C 3 = 10 nF

3000 µF

3.5µH

OU T

VBAT

RC In Filter

RC Out Filter

GND

33981

Filter

RC Out

Filter

RC In

Filter

33981 датащи(PDF) 25 Page - Freescale Semiconductor, Inc

33981 датащи(HTML) 25 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

датащи скачать

ссылки URL