FreeLists / si-list / [SI-LIST] Re: Measurement peaks of current.

[Ravinder.Ajmani@xxxxxxxxxxxxxx]

Zhangkun,
Will you please elaborate why can't we directly use an active differential 
probe across the resistor, instead of connecting it to an Op Amp.
Regards, Ravinder
Server PCB Development
Hitachi Global Storage Technologies

Email: Ravinder.Ajmani@xxxxxxxxxxxxxx




Zhangkun <zhang_kun@xxxxxxxxxx>
Sent by: si-list-bounce@xxxxxxxxxxxxx
08/04/2004 05:55 PM
Please respond to zhang_kun

 
        To:     tal_segev@xxxxxxxxx, si-list@xxxxxxxxxxxxx
        cc: 
        From:   si-list-bounce@xxxxxxxxxxxxx
        Subject:        [SI-LIST] Re: Measurement peaks of current.




Tal

In the CPCI, there is one kind of method to measure the current in the 
power. One  resistor of 5m ohm is used to get the current and the voltage 
between the two terminal of the resistor are input to one IC. In the IC, 
there is one op-amp. This method is similar to yours.

My suggestion is that the trace, which connects the resistor and the IC 
input pin, should be differential pair. Active probe should not be used. 
In our situation, it is difficult to get the exact current in the power 
net.

Hope this will help

Best Regards
Zhangkun
----- Original Message ----- 
From: "Tal Segev" <tal_segev@xxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Thursday, August 05, 2004 4:34 AM
Subject: [SI-LIST] Measurement peaks of current.


> Hi all, 
> 
> I'm designing an embedded system with 8 DDR-SDRAM
> (DDR-1) chips, large FPGA, CPU & so on. Due to the
> amount of current gorges on the design, the result of
> power calculation for this board is about 45W, without
> the VTT and not considering the voltage regulators
> efficiency, (a beet less then a lamp). I personally
> predict that this design will use about 25W in
> average.
> 
> I need to measure the current, especially the peaks of
> the current; I'm considering using a serial 1.5mOhm
> power resistor to measure the current through a scope.
> 
> So (finally), my questions are (I have lot of them).
> * Is it that simple to measure the current, or am I
> naive?
> * Should I use some OP-Amps to isolate the scope from
> the power?
> * should I use active probe, or simple probe will
> content?
> * Can I avoid using a power resistor (its size is
> huge, even the SMD)?
> * Can any one suggest some other way to measure the
> current?
> 
> Thanks for the patience, 
> Tal
> 
> 
> 
> 
> 
> 
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