[SI-LIST] : HSTL Termination

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From: manoj-kumar.sharma@st.com
Date: Wed May 30 2001 - 22:48:34 PDT


attached mail follows:


Hi Vinu,

As you write for Class 1 HSTL driver the output impedence should be
greater than 38 ohms.
What I interprate from this is, to design the driver for voh & Vol (Ioh
and Iol) the minimum load is 38 ohms.
Voh =1.1V, Vol = 0.4 V and Ioh & Iol >= 8mA.

For this specs, say Voh =1.1V, Ioh =8mA, we can have the value of
R=1.1/8m = 137.5ohms,

Can you oblige me by putting some light on how you calculate the minimum
load (ie. how you decide max. current).

Regards
Manoj

------------------------------

Date: Wed, 30 May 2001 10:25:50 -0700
From: Vinu Arumugham <vinu@cisco.com>
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.

>
>

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