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Spartan-3A/3AN FPGA Starter Kit Board User Guide
UG334 (v1.1) June 19, 2008
Chapter 17:
Voltage Supplies
R
Caution!
If the meter offers various current ranges, always start with the largest range first.
Passing too large a current through a meter may damage it.
•
Reapply power to the board.
•
Record the current measurements across the jumper.
•
If the FPGA design supports the power-saving Suspend mode, measure the current
with the SUSPEND switch (see
“SUSPEND Switch,” page 26
) set in both the “RUN”
and “SUSPEND” positions. The default FPGA application shipped with the Starter
Kit board does use the Suspend mode. For additional information on the Suspend
mode, see the “
Power Management Solutions
” chapter in
UG331
:
Spartan-3 Generation
FPGA User Guide
.
•
Convert the current measurement (Amperes or mA) to a power measurement (Watts
or mW), by multiplying the measured result by the supply voltage.
I
2
C Voltage Adjustment Interface
Each LP3906 regulator has an two-wire, I
2
C serial interface that optionally controls various
functions, such as the regulator output voltage. As indicated in
Table 17-3
, the I
2
C interface
can be controlled by the FPGA application using the I/O pins indicated or by some
external controller using the through-hole mounting pads provided on the board, shown
in
Figure 17-1
.
Possible Applications
For experimentation purposes only, Xilinx only recommends adjusting the two supplies
listed below:
•
By default, the V
CCAUX
supply to the FPGA is set to 3.3V, as required for Spartan-3AN
FPGAs. On Spartan-3A FPGAs, V
CCAUX
can be either 2.5V or 3.3V, with potentially
lower power consumption at 2.5V. Consequently, V
CCAUX
can be reduced to 2.5V by
adjusting the LDO1 output on the LP3906 regulator designated IC19. The
corresponding I
2
C control signals are REG1_SCL and REG1_SDA.
•
By default, the reference voltage to Channels C and D on the D/A converter is 3.3V.
However, this voltage can be adjusted to between 1.0V and 3.3V by controlling the
LDO1 output on IC18. The corresponding I
2
C control signals are REG2_SCL and
REG2_SDA. See
Chapter 10, “Digital-to-Analog Converter (DAC)”
for additional
information.
Table 17-3:
I
2
C Voltage Adjustment Interface to Regulator
Regulator
I
2
C Control Input
FPGA Connection
Through-Hole
Connection
IC18
SCL
REG2_SCL
(D11)
REG2-SCL
SDA
REG2_SDA
(F13)
REG2-SDA
IC19
SCL
REG1_SCL
(E13)
REG1-SCL
SDA
REG1_SDA
(D13)
REG1-SDA