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Chapter 6: Board Test System
The Power Monitor
Arria II GX FPGA Development Kit, 6G Edition User Guide
July 2010
Altera Corporation
f
A table with the power rail information is available in the
Arria II GX FPGA
Development Board, 6G Edition Reference Manual
.
Power Information
The
Power information
control displays current, maximum, and minimum power
readings for the following units:
■
mVolt
■
mAmp
■
mWatt
Power Graph
The power graph displays the mWatt power consumption of your board over time.
The green line indicates the current value. The red line indicates the maximum value
read since the last reset. The yellow line indicates the minimum value read since the
last reset.
Graph Settings
The following
Graph settings
controls allow you to define the look and feel of the
power graph:
■
Scale select
—Specifies the amount to scale the power graph. Select a smaller
number to zoom in to see finer detail. Select a larger number to zoom out to see the
entire range of recorded values.
■
Update speed
—Specifies how often to refresh the graph.
Reset
This
Reset
control clears the graph, resets the minimum and maximum values, and
restarts the Power Monitor.
Calculating Power
The Power Monitor calculates power by measuring two different voltages with the
LT2418 A/D and applying the equation
P
=
V
×
I
to determine the power
consumption. The LT2418 measures the voltage after the appropriate sense resistor
(
Vsense
) and the voltage drop across that sense resistor (
Vdif
). The current (
I
) is
calculated by dividing the measured voltage drop across the resistor by the value of
the sense resistor (
I
=
Vdif
/
R
). Through substitution, the equation for calculating
power becomes
P
=
V
×
I
=
Vsense
× (
Vdif
/
R
) = (
Vsense
) × (
Vdif
) × (1/.009), except for
the A2VCC rail which uses .001 for
R
.
You can verify the power numbers shown in the Power Monitor with a digital
multimeter that is capable of measuring microvolts to ensure you have enough
significant digits for an accurate calculation. Measure the voltage on one side of the
resistor (the side opposite the power source) and then measure the voltage on the
other side. The first measurement is
Vsense
and the difference between the two
measurements is
Vdif
. Plug the values into the equation to determine the power
consumption.
