[SI-LIST] Re: Power Consumption of a bus
- From: steve weir <weirsp@xxxxxxxxxx>
- To: "Lucas Bossetti" <Lucas_Bossetti@xxxxxxxxxxx>,<si-list@xxxxxxxxxxxxx>
- Date: Fri, 14 Mar 2003 09:12:58 -0800
Lucas,
Power = Vsupply * (( Vhi - Vlo ) / Zline) * Tflight * SymbolRate / 2, for
an exactly matched series termination, and no cross-conduction in the driver.
Tflight is the one-way propagation down the line. This accounts for the
voltage drop in the drivers, but not the quiescent current, or any cross
conduction.
Basically, what is going on is that when the driver switches high, the
junction of the driver and the Tline swings half of the Vhi-Vlo excursion
for 2 T flight, after which both the driver and the input to the line are
stable at Vhi. So the Q is ((Vhi - Vlo)/( 2 * Zline)) * 2*Tflight, where
the 2s cancel. The energy drawn from the supply is Vsupply * Q.
When the driver switches low, it pulls the charge out of the line, and no
additional power from the supply. The cycle occurs at the binary symbol
rate / 2, yielding power.
Regards,
Steve.
At 10:04 AM 3/14/2003 +0100, Lucas Bossetti wrote:
>Steve,
>I need to estimate the power drawn from the power supply.
>The bus doesn't use parallel terminators.
>
>Thanks
>Lucas
>
>
>
>
>
>----- Original Message -----
>From: "steve weir" <weirsp@xxxxxxxxxx>
>To: <Lucas_Bossetti@xxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
>Sent: Friday, March 14, 2003 9:45 AM
>Subject: [SI-LIST] Re: Power Consumption of a bus
>
>
> >
> > Lucas,
> >
> > First, are you trying to figure out:
> >
> > 1. Power drawn from the power supply?
> > 2. Heat dissipated in the I/O drivers?
> > 3. Both?
> >
> > A good deal of both the AC and DC power drawn from the power supply can go
> > into the terminators and will not appear as heat in the drivers.
> >
> > Regards,
> >
> >
> > Steve.
> > At 08:49 AM 3/14/2003 +0100, Lucas Bossetti wrote:
> >
> > >Could someone tell me how to estimate the power consumption of the I/O
>power
> > >pins of a device?
> > >
> > >Thanks
> > >
> > >Lucas
> > >
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