Datasheet

www.ti.com Theory of Operation
When invalid or incorrect inputs are given to the design tool, text associated with the faulty input will turn
red. Positioning the mouse cursor over the red text will give additional information about any design
conflict.
Component and parametric results are shown to the right as well as the LM5066 safe operational area
(SOA) chart. The SOA chart shows the minimum, typical, and maximum SOA protection areas for a given
design. For a robust design, the SOA of the MOSFET used should be above the MAX protection SOA line
for all operating areas.
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 device is detected and placed. If the values in the design tool are different than
the values on the board, erroneous telemetry and fault data will be reported by the GUI. To return to the
block view of the device, press the Home buttonlocated at the far left in the menu bar.
The design tool is also useful to calculate the PMBus coefficients. With the correct value for current sense
resistor (R
S
) 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 results presented by the design tool can be calculated by hand using the equations provided
in the datasheet. However, note the design tool calculates parameters factoring in worst case tolerances,
while the equations in the datasheet are based on typical thresholds.
11 Theory of Operation
The LM5066 provides intelligent control of the power to a load from a live power source. The three primary
functions of the device are to limit in-rush current during turn-on, monitor the load current for faults during
normal operation, and to provide system telemetry for the following parameters: Input Voltage (VIN), Input
Current (IIN), Input Power (PIN), Output Voltage (VOUT), Auxilliary Voltage (VAUX), and Temperature.
Additional functions include under- and over-voltage lock-outs (UVLO/OVLO) to ensure voltage is supplied
to the load only when the system input voltage is within a specified range, power limiting of the series
pass MOSFET (Q
1
) during turn-on, and a Power Good logic output (PGD) to indicate the output voltage
status.
Upon applying the input voltage to the LM5066, Q
1
is initially held off for the insertion delay (128 ms) to
allow ringing and transients on the input to subside. At the end of the insertion delay, if the input voltage at
V
IN
is above the UVLO threshold, Q
1
is turned on in a controlled manner to limit the in-rush current.
The LM5066 utilizes two methods to limit in-rush currents at startup. For the input voltage range and
sense resistor on this board, the in-rush current will be limited by the MOSFET power limit method. The
power limit method controls the input current such that a constant power is dissipated across Q
1
during
startup. At the onset of the startup period, V
IN
= 48V and V
OUT
= 0V. Q
1
’s power dissipation is limited to a
peak value set by R
PWR
(70W) by monitoring its drain current (the voltage across R
S
) and its drain-to-
source voltage. Their product is maintained constant by controlling the drain current as the drain-to-source
voltage decreases (as the output voltage increases). This is shown in the constant power portion of
Figure 10 where the drain current is increasing to I
LIM
.
9
SNVA487A–August 2011–Revised April 2013 AN-2160 LM5066 Evaluation Board
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