[SI-LIST] Re: IO Power Dissipation in SoC
- From: Ajay Dhingra <ajay.dhingra@xxxxxxxxx>
- To: telegrapher9@xxxxxxxxx
- Date: Sat, 02 Aug 2014 13:50:13 +0530
My fundamental question is if the power dissipation in buffer driver of a
transmitter is dependent on source impedance ( drive strength)or not.
Apparently all the literature takes into account only load cap but no one is
talking about AC Current sourced by transmitter irrespective of load cap.
I really wonder the current which passes through IO buffer of a driver would
really convert to any kind of heat. Apparently current would be sourced just
for few nano seconds, basically for duration of rise/fall time.
While calculating power dissipation in a device can we neglect IO Buffer power
consumption which would be VccQ*IccQ. Where IccQ would vary as per different
drive strength settings.
Thanks
Ajay
Sent from my Huawei Mobile
David Utah <telegrapher9@xxxxxxxxx> wrote:
>When charging/discharging a capacitive load the energy dissipated is
>voltage squared times the load capacitance (plus the driver C). Note that
>energy is dissipated both on charging and discharging the capacitance and
>that's why the 1/2 in the equation you cite, goes away.
>W = (V^2)C
>
>For a resistively terminated load use (V^2)/Rload + (V^2)Cdriver
>
> Dave Cuthbert, NARTE Certified EMC Engineer
> Consultant for analog, instrumentation, power conversion, EMC
>
>
>On Fri, Aug 1, 2014 at 3:10 AM, Ajay Dhingra <Ajay.Dhingra@xxxxxxxxxxx>
>wrote:
>
>> Hi All
>> I was wondering if someone can put a thought on how to calculate power
>> dissipation in the I/Os(Buffer Drivers) of an SoC. Will it be
>>
>> Buffer I/O Supply Voltage(VCCQ) * I/O Current
>>
>> Where I/O Current is as per the drive capability of driver(drive strength).
>>
>> OR it will be
>>
>> =1/2 *{CVF}* V
>>
>> Where C is the load cap
>> V is the I/O voltage amplitude
>> F is the toggle frequency of I/O.
>>
>>
>> OR
>>
>> Both the proposals are wrong. Kindly educate me.
>>
>> Point to note: in first proposal current is independent of Load whereas in
>> second current depends on Load Cap.
>>
>> Thanks
>> Ajay Dhingra
>>
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