Datasheet
GUI Design Page
The GUI assumes the hardware configuration is set to default
evaluation board configuration. If any of the components are
changed, the device hardware configuration needs to be up-
dated in the design tool section. To open the design tool click
the wrench icon located on the LM25056 block representation
which will open the window displayed in Figure 11.
30160337
FIGURE 11. LM25056 GUI Design Tool
Activating the design page pulls several adjustable inputs a
typical applications schematic. Design inputs are keyed in on
the left side of the window.
The input voltage for the LM25056 runs from 3 to 17V. In this
tool, it only shows the range for infomational purposes and is
not used for calculation in the remainder of the window.
The Maximum VAUX1 window is used to calculate the resistor
divider for R
1
and R
2
. The calculator assumes that the maxi-
mum measured value of the VAUX pin is 1.0V. In operation,
the maximum measured value is near 1.2V and the difference
allows for a buffer to the full scale. The tool also assumes that
R
2
is 10.0 kΩ and calculates the required R1 value. Once the
Maximum VAUX1 value is entered, Values for R
1
and R
2
ap-
pear in the Component Results section. The Std. 1% Resis-
tors checkbox will enter in the closest standard 1% values that
are available to the resistors.
The Maximum Load Current window is used to determine the
size of the sense resistor needed based on the current sense
range. The LM25056 has two current sense ranges. The
GAIN=0 has an approximate current sense range of 30mV
across the sense resistor and is the default state. The GAIN=1
sets the current sense range to approximately 60mV. The
current sense range is set with the pull down window on the
left side of the design tool.
Once the Maximum Load Current and the Current Sense
Range windows are set, the current sense resistor is set in
the Current Sense Resistor and Component Results sections.
As a default, a setting of 7.5A as the maximum load current
at the current sense range of 30mV will set the current sense
resistor R
S
to 4 mΩ. Entering these values will also show the
power dissipation of R
S
in the Parametric Results section at
the bottom of the design tool.
The PMBus Slave Address pulldown window shows the pos-
sible PMBus addresses that the LM25056 can be set to
respond to. By selecting the one of the 27 possible addresses,
the necessary connection to the ADR0, ADR1, and ADR2
pins is shown on the circuit diagram. As an example, if 0x17
is selected, the ADR0 would be floating, ADR1 would be con-
nected to VDD, and ADR2 would be grounded. This set of
connections would be shown on the circuit diagram, and can
be tested on the demo board.
Once a design is complete the design should be saved by
selecting the File menu, and then Save. Once the hardware
is modified to match the design the GUI should be restarted
and the hardware configuration file loaded right after the de-
vice is detected and placed. If the values in the design tool
are different than the values on the board, erroneous teleme-
try and fault data will be reported by the GUI. To return to the
block view of the device press the home icon located at the
far left in the menu bar.
The design tool is also useful to calculate the PMBus coeffi-
cients. With the correct value for current sense resistor (RS1)
the tool will calculate the correct coefficients to scale the raw
telemetry data. The coefficients can be viewed by selecting
View from the main menu bar, and then selecting the PMBus
Coefficient Editor. When the PMBus Coefficient Editor is
opened, press the Get All button to show the currently used
coefficients.
If desired the equations used in the design tool can be calcu-
lated by hand using the equations provided in the datasheet.
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