RE: [SI-LIST] : EMC Issue - servo amplifier

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From: Gaines, William (WILLIAM.GAINES@Aerojet.com)
Date: Fri Mar 24 2000 - 07:40:02 PST


In one design, it was not the EMI that drove the design, but just the noise
from the output of the PWM driver. In this case we were driving a heater at
50khz! The analog circuits eventually had to be placed in an entirely
different enclosure. Since this was for a Space application, we were
limited to Radiation hardened devices. (BTW, even with addressing the EMI
issues during the initial design, we still spent a year solving the EMI
issues on this instrument, but that is another story!)

Bill Gaines
Sr. Engineer, Electronic Packaging, Aerojet, Azusa
626-812-2199 m-f 7-3:30 626-969-5772 fax
william.gaines@aerojet.com 626-849-2324 pager

> ----------
> From: Lum Wee Mei[SMTP:lweemei@dso.org.sg]
> Reply To: si-list@silab.eng.sun.com
> Sent: Thursday, March 23, 2000 7:08 PM
> To: 'si-list@silab.eng.sun.com'
> Subject: [SI-LIST] : EMC Issue - servo amplifier
>
> I have a very small design that has a servo amplifier (module) with some
> digital and analog sections. As space is a constraints, the big servo
> amplifier will be on one side while the rest of the components will be
> on the other. I was suggesting, at most 6 layers with L1-S, L2-S,
> L3-DGND, L4-VCC, L5-AGND and L6-S. In the worst case, a very small
> portion of the AGND will need to be used as DGND, if I need to place one
> or two digital components with the servo amp.
>
> The EMC engineer suggested otherwise - 8 layers. The extra 2 layers, are
> for routing a crystal clock signal and its gnd plane. Another
> recommendation by the EMC engineer is that this servo amplifier has to
> be enclosed in a shielded box to prevent EMI. If the PWM provides at
> most 16MHz, do we still require this shielded box as space is a real
> constraint?
>
> I was told in the end, all the grounds are to be shorted at one point.
> If that is the case, which would be the best method to do so, at the
> mating connector or within the board itself?
>
> Any responds will be deeply appreciated.
> Regards - Wee Mei
>
>
>
>
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