Subject: Resending:Multiple Power pin defination

From: [email-masked] (Syed Huq)
Date: Mon, 1 Aug 94 14:40:26 PDT

Resending..
Syed.

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From: [email-masked] ( Bob Ross)
Date: Mon, 1 Aug 94 21:03:37 PDT

Syed and IBIS committee:

You will IBIS Version 2.0 functionality to model RS-232 drivers.  The
[Pulldown reference] and [Gnd clamp reference] keywords in particular
are required to specifiy the pulldown and clamping characteristics that
are referenced to -10V.  I have attached to your example the keywords.
Note, [Voltage range] is still required, but could be omitted if the
keywords [Pullup reference] AND [Power clamp reference] which both 
default to [Voltage range] are also defined.

Your application raises some interesting points and potential interaction
limitations even in the very robust IBIS Version 2.0.  One is that since
you have an internal charge pump supply (which happens to have external
pin in your example) the correlation of a [model] and external POWER sources
available though the optional [Pin mapping] keyword is not directly defined.
IBIS cannot show how the 5V VDD relates to the [model] +/- 10V values.
Secondly, to comply with the INTENT of the pullup and pulldown table
voltage ranges you would need to provide voltages data points at +/- 20V
beyond the rails, i.e., extend to +/- 30 V.  This is not stated explicitly
in the spec.  However, if there are clamps at both ends, then I would
argue that you could in practice reduce the ranges beyond the rails without
any practical effects on any simulator to a reasonable value.

Bob Ross,
Interconnectix, Inc.

> Hello IBIS gurus:

> A question for anyone - >

> I am modeling a RS-232 Driver that uses a Charge pump. So when I apply
> 5V to Vcc, the internal Charge pump doubles the voltage and creates the
> V+ = +10V and V- = -10V as required by the Driver.

> So, in the [Pin] keyword section, I am doing the following:
> -------------------------------------------------------------
> [Pin]	signal_name	model_name
> 1	XXX		XXX
> 2	YYY		YYY
> 3	ZZZ		ZZZ
> 4	VDD		POWER		| 5V is applied here
> 5	V+		POWER		| +10V for V+
> 8	V-		POWER		| -10V for V-
> 9
> 10

> and in the [voltage range] keyword section, I am doing:

> 			typ	min	max
> [voltage range]       10.0V   9.75V   10.25V | for 10V typ

[Pulldown reference]   -10    -9.75    -10.25
[Gnd clamp reference]  -10    -9.75    -10.25

> ---------------------------------------------------------------
> Is my approach correct ?
> How do I know, that V- pin is getting a -10V supply ?
> What is the best way to define a +/- POWER ?
> I am using IBIS v1.1

> Regards,
> Syed huq
> National Semiconductor.

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