RE: [SI-LIST] : HSTL Termination

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From: Jinto N.Jose (jinto.jose@wipro.com)
Date: Wed May 30 2001 - 21:28:10 PDT


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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