Re: [SI-LIST] : HSTL Termination

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From: Paul Levin (levinpa@earthlink.net)
Date: Wed May 30 2001 - 22:07:53 PDT


How about a dc-coupled audio power amplifier? Some of them are spec'd
to drive 4 ohms, and at some frequencies speakers have considerably lower
impedances yet. Check the output current spec's. Be careful about heat-sinking.

Paul Levin
Senior Principal Engineer
Logic Innovations
______________________

"Jinto N.Jose" wrote:

> Do ordinary power supplies sink current ? any suggestions for a 0.75 V
> supply which can source and sink current ?
>
> Jinto
>
> > -----Original Message-----
> > From: vinu@cisco.com [mailto:vinu@cisco.com]
> > Sent: Wednesday, May 30, 2001 10:56 PM
> > To: Jinto N.Jose
> > Cc: SI List
> > Subject: Re: [SI-LIST] : HSTL Termination
> >
> >
> > "Jinto N.Jose" wrote:
> >
> > > Hello Everybody!
> > > One of the suggested termination for HSTL class-I is
> > >
> > > ___ 0.75V
> > > |
> > > /
> > > \ 50 ohms.
> > > /
> > > |\ \ |\
> > > | \_____________|_| \
> > > | / | /
> > > |/ |/
> > >
> > > How is this usually realized ? Do any body use a +0.75
> > power supply for
> > > this ?
> >
> > Yes, this termination with a 0.75V power supply that is capable
> > of sourcing and
> > sinking current, is sometimes used.
> >
> > >
> > > What about the topology shown bellow - is it a valid
> > termination for HSTL- I
> > > signals
> > >
> > > ___ 1.5V
> > > |
> > > /
> > > \ 100 ohms.
> > > /
> > > |\ \ |\
> > > | \_____________|_| \
> > > | / | | /
> > > |/ / |/
> > > \
> > > / 100 ohms
> > > \
> > > |
> > > ---
> > > ///
> > >
> >
> > This is a valid HSTL I termination.
> >
> > >
> > > In all HSTL specifications I have seen , I have found
> > Ioh and Iol min
> > > values and not the max values. What is the significance of this minimum
> > > output current specification ?
> >
> > This spec. guarantees that the driver will source or sink at
> > least Ioh/Iol while
> > meeting Voh/Vol levels.
> >
> > There is no max. Ioh/Iol spec. According to the spec., an HSTL
> > Class II driver is
> > also HSTL Class I compliant. If you plan to use HSTL Class I
> > drivers to drive
> > unterminated lines, you may have to design the buffer to not only
> > meet the HSTL
> > spec. but also limit the output impedance to be greater than
> > about 38 ohm, to
> > avoid overshoot/undershoot.
> >
> >
> > >
> > >
> > > Regards
> > > Jinto
> > >
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