LM5025EVAL National Semiconductor, LM5025EVAL Datasheet - Page 2

• Manufacturer Part Number: LM5025EVAL
• Description: EVALUATION BOARD FOR LM5025
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5025EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 3.3V
• Current - Output: 30A
• Voltage - Input: 36 ~ 72V
• Regulator Topology: Buck
• Frequency - Switching: 230kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5025
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: *LM5025EVAL; *LM5025EVAL/NOPB; LM5025EVAL

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Theory of Operation
Powering and Loading
Considerations
When applying power to the LM5025A evaluation board
certain precautions need to be followed. A failure or mis-
connection can present itself in a very alarming manner.
Proper Connections
When operated at low input voltages the UUT can draw up to
3.5A of current at full load. The maximum rated output cur-
rent for the evaluation board is 30A. Be sure to choose the
correct connector and wire size when attaching the source
supply and the load. Monitor the current into and out of the
UUT (evaluation board or unit under test). Monitor the volt-
age directly at the output terminals of the UUT. The voltage
drop across the load connecting wires will give inaccurate
measurements, this is especially true for accurate efficiency
measurements.
Source Power
The evaluation board can be viewed as a constant power
load. At low input line voltage (35V) the input current can
reach 3.5A, while at high input line voltage (78V) the input
current will be approximately 1.5A. Therefore to fully test the
LM5025A evaluation board a DC power supply capable of at
least 80V and 4A is required. The power supply must have
adjustments for both voltage and current. An accurate read-
out of output current is desirable since the current is not
subject to loss in the cables as voltage is.
The power supply and cabling must present a low imped-
ance to the UUT. Insufficient cabling or a high impedance
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Simplified Active Clamp Forward Converter
2
power supply will droop during power supply application with
the UUT inrush current. If large enough, this droop will cause
a chattering condition upon power up. This chattering condi-
tion is an interaction with the UUT undervoltage lockout, the
cabling impedance and the inrush current
Loading
An appropriate electronic load with specified operation down
to 3.0V minimum is desirable. The resistance of a maximum
load is 0.11Ω. You need thick cables! Consult a wire chart if
needed. If resistor banks are used there are certain precau-
tions to be taken. The wattage and current ratings must be
adequate for a 30A, 100W supply. Monitor both current and
voltage at all times.
Be careful!! The high temperatures reached
by even the most adequately rated resistors
may burn you or melt your benchtop.
Air Flow
Full rated power should never be attempted without provid-
ing the specified 200 CFM of air flow over the evaluation
board. This can be provided by a stand-alone fan.
Powering Up
Using the shutdown pin provided will allow powering up the
source supply with the current level set low. It is suggested
that the load be kept low during the first power up. Set the
current limit of the source supply to provide about 1.5 times
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