Sundance SMT395Q User Manual
Page 21
Version 1.0.7
Page 21 of 31
SMT395Q User Manual
Series resistors are fitted inline with the output of the power supplies (DSP core and
SDRAM) to be measured. The value of these is chosen so that the voltage drop will not
exceed 5% under maximum load.
The other two power supplies (DDR and FPGA core) have series resistors, but the output
from the resistor is fed back to the power supply. This ensures that the device always
receives the correct voltage. The voltage on the power supply side of the resistor will
therefore be higher.
The ADC within the MSP430 allows for several different voltage references (internal and
external). It is a 12 bit converter, so can produce 4096 codes over the input voltage range
Vref- to Vref+.
The table below shows the ADC parameters. ‘#’ refers to the number of different ADC codes
produced over the series resistor voltage drop range.
Device Voltage
Current Resistor
voltage drop
Vref+ Vref- #
SDRAM &
DSP I/O
3.3 1.00
0.165
(5% of 3.3)
3.3 0 205
FPGA core
1.5
10.00
0.1*
2.5
0
164
DDR 2.5 1.00
0.1* 2.5
0
124
DSP core
1.2
1.00
0.060
(5% of 1.2)
2.5 0 164
*Voltage drop is set and then the resistor value calculated.
E.g. For FPGA, set voltage drop to 0.1V, then R = 0.1/10 = 10mOhms. Larger voltage drops
may be possible which would increase #.
The micro-controller (MPS430F148) continuously monitors all parameters. All voltage
measurements (and the FPGA core temperature) are via the 4-bit data bus to the FPGA.
A pre-set maximum FPGA core temperature is programmed into the micro-controller. If this
temperature is exceeded, then the micro-controller will force the FPGA into an un-configured
and non-operational state.
For greater power measurement accuracy, the voltages across the series resistors can be
monitored using an external volt-meter.
Alternatively, the resistors could be removed and ammeters inserted for direct current
measurement. It is suggested that this is NOT undertaken, as failure to ensure all power
supplies are within tolerances (i.e. If an ammeter is not in circuit when power is applied), may
result in device damage.