Re: [SI-LIST] : HSTL Termination

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From: Vinu Arumugham (vinu@cisco.com)
Date: Wed May 30 2001 - 10:25:50 PDT


"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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